serv1857 785c (1hw), 785d (msy), 789c 2bs)_txt[1].pdf

SERV1857 June 2008

TECHNICAL PRESENTATION

785C (1HW), 785D (MSY), 789C (2BW)LARGE OFF-HIGHWAY TRUCKS

Service Training Meeting Guide(STMG

SERVICE TRAINING

785C (1HW), 785D (MSY), 789C (2BW) LARGE OFF-HIGHWAY TRUCKS TEXT REFERENCE

AUDIENCE

Level II--Service personnel who understand the principles of machine systems operation, diagnostic equipment, and procedures for testing and adjusting.

CONTENT

This presentation provides basic maintenance information and describes the systems operation of the engine, power train, steering, hoist, and the air system and brakes for the 785C/789C Off-highway Trucks. The Automatic Retarder Control (ARC) and the Traction Control System (TCS) are also discussed.

OBJECTIVESAfter learning the information in this meeting guide, the serviceman will be able to:

1. locate and identify the major components in the engine, power train, steering, hoist and the air system and brakes;

2. explain the operation of the major components in the systems; and3. trace the flow of oil or air through the systems4. identify what is new and different on the 785D 3512C HD engine along with RAXL

filtration

REFERENCES

784C Tractor/785C Truck Service Manual SENR1485784C Tractor/785C Truck Operation and Maintenance Manual SEBU7173785C Truck with High Altitude Arrangement (HAA) Operation and Maintenance Manual SEBU7176789C Truck Service Manual SENR1515789C Truck Operation and Maintenance Manual SEBU7174Cold Weather Recommendations for Caterpillar Machines SEBU5898Caterpillar Machine Fluids Recommendations SEBU6250

PREREQUISITES

Interactive Video Course "Fundamentals of Mobile Hydraulics" TEMV9001Interactive Video Course "Fundamentals of Electrical Systems" TEMV9002STMG 546 "Graphic Fluid Power Symbols" SESV1546

Estimated Time: 24 Hours Visuals: 268 Visuals Serviceman Handouts: 16 Data Sheets Form: SERV1857

© 2008 Caterpillar Inc. Date: 06/08

SERV1857 - 3 - Text Reference06/08

SUPPLEMENTAL MATERIAL

Reference Manuals

Fluid Power Graphic Symbols User's Guide SENR3981Flexxaire™ Fan Installation and Maintenance Manual SEBC1152Automatic Lubrication System SENR4724Off-Highway Truck/Tractors Vital Information Management System (VIMS)--System Operation" RENR2630Off-Highway Truck/Tractors Vital Information Management System (VIMS)--Testing and Adjusting Troubleshooting" RENR2631Variable Speed Fan Clutch" SENR8603Oil Renewal System" RENR2223Off-Highway Truck/Tractors Brake Electronic Control System" SENR1503

Specification Sheets

785C Off-highway Truck AEHQ5320789C Off-highway Truck AEHQ5321793C Update Off-highway Truck AEHQ5186

Salesgrams and Product Bulletins

Salesgram "Vital Information Management System (VIMS)" TELQ4478Training Bulletin "Caterpillar Transmission/Drive Train Oil" TEJB1002Product Bulletin "Reporting Particle Count By ISO Code" PEJT5025Salesgram "Caterpillar Extended Life Coolant" TEKQ0072Salesgram "785C/789C/793C Mining Truck Introduction" TELQ4459Salesgram "Cat 769, 771, 773, 775, 777, 785 and 789 Flexxaire™ FanCustom Attachment" TELQ4010Product Bulletin "793C Off-highway Truck" TEJB3060

Video Tapes

793C Off-highway Truck--Service Introduction SEVN4016793C Off-highway Truck--Marketing Introduction AEVN3742Suspension Cylinder Charging TEVN2155Introduction to the Automatic Electronic Traction Aid (AETA) SEVN91873500 Engines--EUI Service Introduction SEVN2241Mining Trucks--Cleanliness and Component Life SEVN4142

Booklets

Know Your Cooling System SEBD0518Diesel Fuels and Your Engine SEBD0717Oil and Your Engine SEBD0640C-Series Mining Trucks--3500B Diesel Engines LEDH8400

Special Instructions

Repair of 4T8719 Bladder Accumulator Group" SEHS8757Using 1U5000 Auxiliary Power Unit (APU)" SEHS8715Using the 1U5525 Attachment Group" SEHS8880Suspension Cylinder Servicing SEHS9411



TABLE OF CONTENTSINTRODUCTION ........................................................................................................................7

WALK AROUND INSPECTION ...............................................................................................11

OPERATOR'S STATION ............................................................................................................45

ENGINE ......................................................................................................................................65Engine Electronic Control System .......................................................................................66Cooling System .....................................................................................................................88Lubrication System ...............................................................................................................97Fuel System .........................................................................................................................101Air Induction and Exhaust System .....................................................................................106

POWER TRAIN .......................................................................................................................111Torque Converter ................................................................................................................112Torque Converter Hydraulic System ..................................................................................115Transmission and Transfer Gears ........................................................................................125Transmission Hydraulic System .........................................................................................128Differential ..........................................................................................................................138Final Drives .........................................................................................................................143Transmission/Chassis Electronic Control System ..............................................................144

STEERING SYSTEM ..............................................................................................................154

HOIST SYSTEM ......................................................................................................................187

AIR SYSTEM AND BRAKES .................................................................................................207Air Charging System ...........................................................................................................209Brake Systems .....................................................................................................................216

BRAKE ELECTRONIC CONTROL SYSTEM .......................................................................236Automatic Retarder Control (ARC) ....................................................................................239Hydraulic Automatic Retarder Control (HARC) ................................................................245Traction Control System (TCS) ..........................................................................................255

OPTIONAL EQUIPMENT .......................................................................................................263FlexxaireTM Fan ................................................................................................................263

785D LARGE OFF-HIGHWAY TRUCKS ..............................................................................2663512C High Displacement Engine ......................................................................................267Right Side Engine Components ..........................................................................................268Left Side Engine Components ............................................................................................269Front Engine Components ..................................................................................................270Rear Engine Components ...................................................................................................271Turbocharger Location ........................................................................................................272Engine Electronic Control Module Diagram ......................................................................273

Engine ECM and Atmospheric Pressure Sensor .................................................................275Primary Speed/Timing Sensor ............................................................................................280Engine Speed Sensor ...........................................................................................................281Coolant Temperature Sensor ...............................................................................................282Coolant Flow Switch...........................................................................................................283Crankcase Pressure Sensor .................................................................................................284Turbo Inlet Pressure Sensors (Taken on the Truck) ............................................................285Intake Manifold Air Temperature Sensor ............................................................................287Intake Manifold Pressure Sensor (Boost) ...........................................................................288Left and Right Side Exhaust Temperature Sensors .............................................................290Fuel Filter Differential Switch ............................................................................................292Filtered and Unfiltered Engine Oil Pressure Sensors .........................................................293Fuel System Diagram ..........................................................................................................299Fuel System Diagram (Fuel Priming) .................................................................................302Top Center Position .............................................................................................................303Valve Lash ...........................................................................................................................304Steering and Front Brake Oil Cooling System ...................................................................305Air Induction and Exhaust System "D" Series Truck .........................................................3073512D HD Engine with ATAAC .........................................................................................309785D Truck Rear Axle Lubrication (RAXL) ......................................................................310"D" Series RAXL filtration (Warm Oil) .............................................................................311RAX Lubrication Strategy ..................................................................................................314RAXL Control Valve ...........................................................................................................316RAXL Pump Drive Oil Diverter Solenoid Relay Control ..................................................318Differential Lube .................................................................................................................320RAXL Final Drive Bypass Valve ........................................................................................321RAXL Motor and Pump ......................................................................................................323Temperature and Pressure Sensors for the RAXL ..............................................................324

CONCLUSION .........................................................................................................................326

HYDRAULIC SCHEMATIC COLOR CODE .........................................................................327

VISUAL LIST ...........................................................................................................................329

SERVICEMAN'S HANDOUTS ...............................................................................................333

NOTES


INTRODUCTION

Shown is the 789C Off-highway Truck. The "C" Series trucks are the same as the "B" Series except for the following changes: 3500B engines, improved cab, two different Electronic Control Modules (Transmission/Chassis and Brake) and an electronically controlled hoist. The 789C also has a 40% larger cooling system with a shunt tank located above the radiator.

The second generation Electronic Programmable Transmission Control (EPTC II) has been replaced with the Transmission/Chassis Electronic Control System. The Transmission/Chassis Electronic Control Module (ECM) controls the same functions as the EPTC II plus the hoist and some other functions.

The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control modules have been replaced with one Brake System ECM. The Brake System ECM controls both the ARC and the TCS functions. The TCS is now connected to the CAT Data Link and the Electronic Technician (ET) service tool can be used to diagnose the TCS.

The load carrying capacities and the Gross Machine Weights (GMW) of the "C" Series trucks are:785C: 118 to 136 Metric tons (130 to 150 tons) 249480 kg (550000 lb.) GMW

789C: 154 to 177 Metric tons (170 to 195 tons) 317520 kg (700000 lb.) GMW

1


785C, 785D, AND 789C LARGE OFF-HIGHWAY TRUCKS

© 2008 Caterpillar Inc.


2

Shown is the right side of a 789C truck. The large air tank on the right platform supplies air for starting the truck and for the service and retarder brake system.

The hoist, brake, and torque converter hydraulic tank (rear) and the transmission hydraulic tank (front) are also visible. The transmission hydraulic system is separate from all the other hydraulic systems.

Shown is the front of a 789C truck. The 789C is similar in appearance to the 793C and may be difficult to identify from a distance. The 793C can be identified by the four air filters and the diagonal access ladder. The 789C has only two air filters and is equipped with two vertical ladders.

The "C" Series trucks use a folded core radiator. The folded core radiator provides the convenience of repairing or replacing smaller individual cores.

3


4


The truck bodies on "C" Series trucks are mandatory options. Two body styles are available for the "C" Series trucks:

- A 12 degree flat floor design that provides uniform load dumping, excellent load retention, and a low center of gravity.

- A dual-slope design with a "V" bottom main floor to reduce shock loading, center the load, and reduce spills.

All internal wear surfaces of the truck bodies are made with 400 Brinell hardness steel. All attachment body liners are also made with 400 Brinell hardness steel. The external components of the bodies are made of steel with a yield strength of 6205 bar (90000 psi).

The forward two-thirds of the body floor is made with 20 mm (.79 in.) thick 400 Brinell steel plate. The rear one-third of the body floor is made with a 10 mm (.39 in.) thick 400 Brinell sub plate and a 20 mm (.79 in.) thick 400 Brinell body grid liner plate. As an option, the grid liner plate can be made with 500 Brinell steel.

The rear suspension cylinders absorb bending and twisting stresses rather than transmitting them to the main frame.

5

WALK AROUND INSPECTION

Before working on or operating the truck, read the Operation and Maintenance Manual thoroughly for information on safety, maintenance, and operating techniques.

Safety Precautions and Warnings are provided in the manual and on the truck. Be sure to identify and understand all symbols before starting the truck.

The first step to perform when approaching the truck is to make a thorough walk around inspection. Look around and under the truck for loose or missing bolts, trash build-up and for coolant, fuel, or oil leaks. Look for indications of cracks. Pay close attention to high stress areas as shown in the Operation and Maintenance Manual.

INSTRUCTOR NOTE: The form numbers for the Operation and Maintenance Manuals are provided under "References" on Page 2.


��

��

��

��

6

The following list identifies the items that must be serviced every 10 Hours or Daily.

- Walk around inspection: Check for loose or missing bolts, leaks, and cracks in frame structures

- Suspension cylinders: Measure/recharge- Transmission oil: Check level- Hoist, converter and brake system oil: Check level- Rear axle oil: Check level- Fuel tank: Drain moisture- Engine crankcase oil: Check level- Radiator: Check level and radiator core plugging- Air filters and precleaners: Check restriction indicators and precleaner dirt level- Steering system oil: Check level- Air tanks: Drain moisture- Brakes: Check operation- Indicators and gauges: Test operation- Seat belt: Inspect- Back-up alarm: Test operation- Secondary steering: Test operation


��

��

��

��

��

�� !��"��

��

��#��$��

%��&�� '��

��(��

��)��

%��"�*��

��+��)��'��

��+��)��'�� ,��

��

!��-��(��)��

��

��&��(��)��++��

��(��%��.�+��!��$��

��/��

��0��!��

!��-��

��1� ��0��

�� "�� ,�� (��%��

��)��(.�+��&

23�'�4!�/#�"�5�$�"�%��'��6�

The front wheel bearing oil level is checked and filled by removing the plug (1) in the center of the wheel bearing cover. The oil should be level with the bottom of the plug hole. The fill plug is a magnetic plug. Inspect the fill plug weekly for metal particles. If any metal particles are found, remove the wheel cover and inspect the bearings for wear. The oil is drained by removing the drain plug (2).

The service interval for changing the front wheel bearing oil is 500 hours.

Use only Final Drive and Axle Oil (FDAO) or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer. FDAO and TDTO TO-4 provides increased lubrication capability for bearings.

Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure can cause heat build-up in the tire and accelerate tire wear.

NOTE: Care must be taken to ensure that fluids are contained while performing any inspection, maintenance, testing, adjusting and repair of the machine. Be prepared to collect the fluid in suitable containers before opening any compartment or disassembling any component containing fluids. Refer to the "Tools and Shop Products Guide" (Form NENG2500) for tools and supplies suitable to collect and contain fluids in Caterpillar machines. Dispose of fluids according to local regulations and mandates.

7


1

2

Check the front suspension cylinders for leaks or structural damage. Check the charge condition of the front suspension cylinders when the truck is empty and on level ground. Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged. Recharge the cylinders with oil and nitrogen if necessary.

Inspect the condition of the front wheel bearing axle housing breather (1). The breather prevents pressure from building up in the axle housing. Pressure in the axle housing may cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies.

Two grease outlet fittings (2) are located on the front of each suspension cylinder. The grease supply line for the Auto Lubrication System is located at the rear of the suspension cylinder. No grease outlet fittings should be located on the same side of the suspension cylinder as the grease fill location. An outlet fitting positioned on the same side of the suspension cylinder as the grease fill location will prevent proper lubrication of the cylinder.

Make sure that grease is flowing from the outlet fittings to verify that the suspension cylinders are being lubricated and that the pressure in the cylinders is not excessive.

INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

8


1

2

On the 785C truck, an air filter housing and a precleaner are located behind the front wheels on both sides of the truck. Check the dust valves (1) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning.

The dust valve is OPEN when the engine is OFF and closes when the engine is running. The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the service life of the air filters will be reduced. Replace the rubber dust valve if it becomes hard and brittle.

The "C" Series trucks may have the optional primary fuel filters with a water separator (2). Two primary filter/water separators are installed, one on each side of the truck. Open the drain valve at the bottom of each housing to drain the water when required. The drain interval is determined by the humidity of the local climate.

Replace the filter element in each housing every 500 hours or when restricted. The filter elements are removed from the top of the housings.

9


1

2

Shown is the right side of the 3512B engine used in the 784C tractor and 785C truck.

Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (arrow) located in the tube between the engine oil cooler and the engine oil filters.

10


Located behind the right front tire is the transmission charging filter (1), the transmission lube filter (2), and the torque converter charging filter (3). Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).

An oil filter bypass switch is located on each filter. The transmission oil filter bypass switches provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends the signals to the VIMS, which informs the operator if the filters are restricted. The torque converter charging filter bypass switch provides an input signal directly to the VIMS.

One of the three injector banks (5) for the automatic lubrication system is also in this location. These injectors are adjustable and regulate the quantity of grease that is injected during each cycle.

A solenoid air valve provides a controlled air supply for the automatic lubrication system. The solenoid air valve is controlled by the Vital Information Management System (VIMS), which energizes the solenoid ten minutes after the machine is started. The VIMS energizes the solenoid for 75 seconds before it is de-energized. Every 60 minutes thereafter, the VIMS energizes the solenoid for 75 seconds until the machine is stopped (shut down). These settings are adjustable through the VIMS keypad in the cab (LUBSET and LUBMAN).

INSTRUCTOR NOTE: For more detailed information on servicing the automatic lubrication system, refer to the Service Manual module "Automatic Lubrication System" (Form SENR4724).

11


12

3

45

Shown are the transmission hydraulic tank (1) and the hoist, converter and brake hydraulic tank (2). Both tanks are equipped with oil level sight gauges.

The oil level of both hydraulic tanks should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running.

The lower sight gauge (3) on the hoist, converter and brake hydraulic tank can be used to fill the tank when the hoist cylinders are in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge.

Inspect the hoist, converter and brake hydraulic tank breather (4), and the transmission hydraulic tank breather (behind the mud flap) for plugging.

When filling the hydraulic tanks after an oil change, fill the tanks with oil to the FULL COLD mark on the sight gauge. Turn on the engine manual shutdown switch (see Visual No. 25) so the engine will not start. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fills the hydraulic systems. Add more oil to the tanks to raise the oil level to the FULL COLD mark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oil level stabilizes at the FULL COLD mark.

Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Add more oil to the tank as required to raise the oil level to the FULL WARM mark.

12


1

2

3

4

In both tanks, use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 or newer.

TDTO TO-4 oil:

- Provides maximum frictional capability required for clutch discs used in the transmission, torque converter and brakes.

- Increases rimpull because of reduced slippage.

- Increases brake holding capability by reducing brake slippage.

- Controls brake chatter.

- Provides maximum frictional capability required for gears.

NOTICEFailure to correctly fill the hydraulic tanks after an oil change may cause component damage.


The rear axles are equipped with double reduction planetary-type final drives (see Visual No. 122). Rotate the final drive until the cover and plug are positioned as shown. The final drive oil level is checked and filled by removing the magnetic plug (arrow). The oil should be level with the bottom of the plug hole. Fill the rear axle housing with oil before filling the final drives with oil. Allow enough time for the oil to settle in all of the compartments. This can be as much as 20 minutes during cold temperatures.

The magnetic inspection plugs should be removed weekly from the final drives and checked for metal particles. For some conditions, checking the magnetic plugs is the only way to identify a problem which may exist.

Use only Final Drive and Axle Oil (FDAO) or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer. FDAO and TDTO TO-4 oil provides:

- Maximum lubrication capability required for gears.- Increased lubrication capability for bearings.

NOTICE

The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

13


The differential oil level is checked by viewing the oil level sight glass (1). The oil should be level with the bottom of the inspection hole.

Two oil level sensors (2) provide input signals to the Brake ECM. The Brake ECM sends the signals to the VIMS, which informs the operator of the rear axle oil level. A rear axle oil filter (3) removes contaminants from the rear axle housing.

Check the rear suspension cylinders for leaks or structural damage. Check the charge condition of the rear suspension cylinders when the truck is empty and on level ground. Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged. Recharge the cylinders with oil and nitrogen if necessary.

The second of three injector banks (4) for the automatic lubrication system is mounted on the top rear of the differential housing.

Above the lubrication injectors is a breather (5) for the rear axle. Inspect the condition of the breather at regular intervals. The breather prevents pressure from building up in the axle housing. Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies.

INSTRUCTOR NOTE: For more detailed information on servicing the suspension system, refer to the Special Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

14


12 2

3

4

5

The cable that holds the body up is stored below the rear of the body. Whenever work is to be performed while the body is raised, the safety cable must be connected between the body and the rear hitch to hold the body in the raised position.

The space between the body and the frame becomes a zero clearance area when the body is lowered. Failure to install the cable can result in injury or death to personnel working in this area.

15


The fuel tank is located on the left side of the truck. The fuel level sight gauge (arrow) is used to check the fuel level during the walk around inspection.

The percentage of sulfur in the fuel will affect the engine oil recommendations. The following is a summary of fuel sulfur and oil recommendations:

1. Use API CH-4 performance oils.2. With fuel sulfur below 0.5%, any API CH-4 oils will have a sufficient Total Base

Number (TBN) for acid neutralization.3. For fuel sulfur values above 0.5%, the new oil TBN should be a minimum of 10 times

the fuel sulfur.4. When 10 times the fuel sulfur exceeds the oil TBN, reduce the oil change interval to

approximately one-half the normal change interval.

16


The primary fuel filter (1) is mounted on the inner side of the fuel tank.

Open the drain valve (2) to remove condensation from the fuel tank.

A fuel level sensor (3) is also located on the fuel tank. The fuel level sensor emits an ultrasonic signal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonic signal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signal changes as the fuel level changes. The fuel level sensor provides the input signals to the VIMS, which informs the operator of the fuel level. A category level 1 warning (FUEL LVL LO) is shown on the VIMS display if the fuel level is less than 15%. A category level 2 warning (FUEL LVL LO ADD FUEL NOW) is shown on the VIMS display if the fuel level is less than 10%.

The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of the sensor, connect a multimeter between Pins 1 and 2 of the sensor connector. Set the meter to read "DC Volts."

The fuel level sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the fuel level. To check the output signal of the fuel level sensor, connect a multimeter between Pins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depth and 84% at 2000 mm (78.8 in.) of fuel depth.

17


1

2

3

Located in front of the fuel tank is the parking brake release filter (1) and the torque converter outlet screen (2).

An oil filter bypass switch is located on each housing. The parking brake filter bypass switch provides an input signal to the Brake ECM and the torque converter outlet screen bypass switch provides an input signal to the VIMS. The Brake ECM sends the signal to the VIMS, which informs the operator if the filter or screen are restricted.

The 789C trucks have two air dryers (3) to accommodate the larger four-cylinder air compressor. Shown is the rear of the two air dryers.

The third injector bank for the automatic lubrication system is also located in this area.

18


2

3

Inspect the condition of the three breathers (1) (two visible) for the brake cylinders. The third breather is located on the front brake master cylinder behind the cross tube. Oil should not leak from the breathers. Oil leaking from the breathers is an indication that the oil piston seals in the brake cylinder need replacement. Air flow from the breathers during a brake application indicates that the brake cylinder air piston seals need replacement.

If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause an indicator rod to extend and open the brake overstroke switch (2). The switch provides an input signal to the VIMS, which informs the operator of the condition of the service and retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning.

19


11

2 2

On the 789C truck, the second air dryer (1) is located in front of the left front suspension cylinder. On the 785C truck, the only air dryer is located here.

The air system can be charged from a remote air supply through a ground level connector (2) inside the left frame.

Engine oil can be added at the quick fill connector (3).

Use only Diesel Engine Oil (DEO) with a specification of CF-4 or newer. DEO oil with a CH-4 specification is available and should be used if possible.

CH-4 engine oil:

- Requires more performance tests than previous oils, such as CE or CF, and has a narrower performance band.

- Can withstand higher temperatures before coking and has better dispersing capability for controlling soot.

- Has better fuel sulfur neutralization capability.

20


1

2

3

The engine oil filters (789C shown) are located on the left side of the engine. Engine oil should be added at the fill tube (1) and checked with the dipstick (2). The 785C has three engine oil filters and is checked and filled through the engine cover (see Visual No. 22).

On the 789C truck, engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3). (For the 785C truck, see Visual No. 10.).

The engine lubrication system is equipped with two oil pressure sensors (4). A sensor is located on each end of the oil filter base. One sensor measures engine oil pressure before the filters. The other sensor measures oil pressure after the filters. The sensors provide input signals to the Engine Electronic Control Module (ECM). The ECM provides input signals to the VIMS, which informs the operator of the engine oil pressure. Together, these sensors inform the operator if the engine oil filters are restricted.

Use only Diesel Engine Oil (DEO) with a specification of (CF-4) or newer. DEO oil with a (CH-4) specification is available and should be used if possible.

- CH-4 engine oil requires more performance tests than previous oils, such as CE or CF, and has a narrower performance band.

- CH-4 engine oil can withstand higher temperatures before coking and has better dispersing capability for controlling soot.

- CH-4 engine oil has better fuel sulfur neutralization capability.

21


1

2

3

4

Shown is the 3512B engine used in the 785C truck. Three oil filters are located on the left side of the engine. The 3512B engine also has a fitting (1) that can be used to drain the engine oil that is trapped above the filters. Do not add oil through the fitting because unfiltered oil will enter the engine. Any contamination could cause damage to the engine.

Aftercooler coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap that is installed at the location of the pipe plug (2).

NOTICEWhen changing the engine oil filters, drain the engine oil that is trapped above the oil filters through the fitting (1) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine.

22


2

1

Engine oil can be added through a high speed oil change connector and will enter the oil pan through the fitting (1).

An engine oil level switch (2) provides input signals to the Engine ECM. The Engine ECM provides an input signal to the VIMS, which informs the operator of the engine oil level.

The oil level switch tells the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.

23


1

2

The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed.

A fuel filter bypass switch (2) is located on the filter base. The bypass switch provides an input signal to the Engine ECM. The Engine ECM sends the signal to the VIMS, which informs the operator if the filters are restricted.

NOTE: If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.

24


12

Before climbing the truck ladder, make sure that the manual engine shutdown switch (1) is OFF. The engine will not start if the manual shutdown switch is ON. If necessary, the switch can be used to stop the engine from the ground level. Operate the switch periodically to check the secondary steering system.

The toggle switches (2) control the lights in the engine compartment and above the access ladder.

The RS-232 service connector (3) is used to connect a laptop computer with VIMS PC software to upload new source and configuration files, view real time data or download logged information from the VIMS.

The battery disconnect switch (4) and VIMS service connector key switch (5) must be in the ON position before the laptop computer with VIMS software will communicate with the VIMS.

The blue service lamp (6) is part of the VIMS. When the key start switch is turned to the ON position, the VIMS runs through a self test. During the self test, the service lamp will flash three times if any logged events are stored in the VIMS main module and once if no logged events are stored.

During normal operation, the service lamp will turn ON to notify service personnel that the VIMS has an active data (machine) or maintenance (system) event. The service lamp flashes to indicate when an event is considered abusive to the machine.

25


1

2

3

4

5

6

Shown is the 789C truck. While climbing the ladder, make a thorough inspection of the radiator. Be sure that no debris or dirt is trapped in the cores. Check the air filter restriction indicators (1) located on both sides of the truck. If the yellow pistons are in the red zone (indicating that the filters are plugged), the air filters must be serviced. Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. Replace the dust valve if the rubber is not flexible.

The VIMS will also provide the operator with an air filter restriction warning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filter restriction.

Two filter elements are installed in the filter housings. The large element is the primary element and the small element is the secondary element.

Air intake system tips:

- The primary element can be cleaned a maximum of six times.- Never clean the secondary element for reuse. Always replace the secondary element.- Air filter restriction causes black exhaust smoke and low power.- A 0.6°C (1°F) increase in intake temperature increases exhaust temperature 1.8°C (3°F).- Exhaust temperature should not exceed 750°C (1382°F).

26


1

2

Shown is a 789C truck. The capacity of the 789C cooling system has been increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.). The radiator is larger and a shunt tank (1) has been added above the radiator.

The cooling system on the "C" Series trucks is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. These two systems are not connected. When servicing the cooling systems, be sure to drain and fill both systems separately.

The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the two coolant levels.

The water used in the cooling system is critical for good cooling system performance. Use distilled or deionized water whenever possible to prevent acids or scale deposits in the cooling system. Acids and scale deposits result from contaminants that are found in most common water sources.

Never use water alone. All water is corrosive at engine operating temperatures without coolant additives. Also, water alone has none of the lubrication properties which are required for water pump seals.

27


1 2

The "C" Series trucks are filled at the factory with Extended Life Coolant (ELC). If ELC is maintained in the radiator, it is not necessary to use a supplemental coolant additive. If more than 10% of conventional coolant is mixed with the ELC, a supplemental coolant additive is required.

With conventional coolant, maintain a 3 to 6% concentration of supplemental coolant additive.- Too much additive will form insoluble salts that cause water pump seal wear, plugging and

will coat parts with excessive deposits that prevent heat transfer.- Not enough additive will result in severe cavitation erosion which will pit and corrode

cylinder liner and block surfaces.

Maintain a 30 to 60% concentration of Caterpillar Antifreeze.- More than 60% antifreeze concentration will reduce freeze protection and cause radiator

plugging.- Less than 30% antifreeze concentration will result in cavitation erosion, which will pit and

corrode cylinder liner and block surfaces and decrease water pump life.- Most commercial antifreezes are formulated with high silicate content for gasoline engines

and are not recommended for diesel engines.

The engine should operate between 88 and 99°C (190 and 210°F).- Operating below this temperature range will cause overcooling problems.- Operating above this temperature range will cause overheating problems.

Cooling system pressure should be between 55 and 110 kPa (8 and 16 psi).- Raising the pressure raises the boiling point. If the pressure is inadequate, the coolant will

boil over and the engine will overheat.

Do not fill the cooling system faster than 20 L/min. (5 gpm).- Filling the cooling system faster than 20 L/min. (5 gpm) will cause air pockets that could

produce damaging steam.

Keep the fan belts adjusted.

Keep the radiator cooling fins straight and clean.


Shown is a 785C truck. The air cleaner indicators (1) are located on the filter housings. If the yellow pistons are in the red zone (indicating that the filters are plugged), the air cleaners must be serviced.

Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. Replace the dust valve if the rubber is not flexible.

28


11

2

The ether cylinders (arrow) are located in the engine compartment behind the radiator. Make sure the ether cylinders are not empty.

The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds.

The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 48). The manual ether injection duration is 5 seconds.

Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm.

Ether starting tip:

- Cold weather causes rough combustion and white exhaust smoke from unburned fuel. Ether injection will reduce the duration and severity of unburned fuel symptoms.

29


The batteries are located below the access panel on the right platform. Inspect the battery connections for corrosion or damage. Keep the battery terminals clean and coated with petroleum jelly.

Inspect the electrolyte level in each battery cell, except for maintenance free batteries. Maintain the level to the bottom of the fill openings with distilled water.

Batteries give off flammable fumes that can explode resulting in personal injury.

Prevent sparks near batteries. They could cause vapors to explode.

Do not allow jumper cable ends to contact each other or the machine.

Do not smoke when checking battery electrolyte levels. Electrolyte is an acid and can cause personal injury if it contacts skin or eyes.

Always wear eye protection when starting a machine with jumper cables.

Always connect the battery positive (+) to battery positive (+) and the battery negative (-) to the stalled machine frame (-).

30


Located on the right platform are the automatic lubrication system grease tank (1), the main air system tank (2), and the steering system tank (3).

Check the level of the grease in the automatic lubrication system tank with the grease level indicator located on top of the tank.

A drain valve is located at the bottom right of the main air system tank. Drain the condensation from the air tank each morning.

31


1

23

The oil level for the steering system tank is checked at the upper sight gauge (1) when the oil is cold and the engine is stopped. After the engine is started, the oil level will decrease as the oil fills the steering accumulators.

After the accumulators are filled, the oil level should be checked again at the lower sight gauge (2). When the engine is running and the accumulators are fully charged, the oil level should not be below the ENGINE RUNNING marking of the lower gauge. If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity.

Before removing the cap to add oil to the steering system, be sure that the engine was shut off with the key start switch, and the steering oil has returned to the tank from the accumulators. Then, depress the pressure release button (3) on the breather to release any remaining pressure from the tank.

Also located on the tank are the main steering oil filter (4) and the steering pump case drain filter (5).

If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at the connector (6) to charge the steering accumulators. Steering capability is then available to tow the truck.

32


1

2

3 4

5

6

INSTRUCTOR NOTE: For more detailed information on servicing the steering accumulators, refer to the Special Instruction "Repair of 4T8719 Bladder Accumulator Group" (Form SEHS8757). For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)"(Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).


Another small air tank (not visible) is located behind the cab (see Visual No. 178). The air tank behind the cab supplies air to the parking and secondary brakes. Drain the moisture from the tank daily with the drain valve (arrow).

33


The windshield washer reservoir (1) is located in the compartment in front of the cab. Keep the reservoir full of windshield washer fluid.

The air conditioner filter (2) is also located in the compartment in front of the cab. Clean or replace the filter element when a reduction of circulation in the cab is noticed.

34


1

2

The remaining 10 Hours or Daily checks are performed in the operator's compartment:

- Brakes: Check operation- Indicators and gauges: Test operation- Seat belt: Inspect- Back-up alarm: Test operation- Secondary steering: Test operation

The brakes are checked by engaging one of the brake systems and placing the shift lever in FIRST FORWARD. Accelerate the engine until the truck moves. The truck must not move below 1200 rpm. This procedure should be repeated for each brake lever or pedal.

The cab fresh air filter is located behind the cover (arrow). Clean or replace the cab fresh air filter when necessary.

INSTRUCTOR NOTE: Refer to the Operation and Maintenance Manual for more information on the remaining tests performed in the cab.

35


OPERATOR'S STATION

The operator's station for the "C" Series Off-highway Trucks has been changed to improve operator comfort and ergonomics. The "C" Series cab now resembles the cab used on the smaller "D" Series Off-highway Trucks.

The VIMS controls the Truck Payload Measurement System (TPMS) on the 785C and 789C trucks. There are two sets of TPMS external loading lamps on the truck. One set of lamps is on the left side of the cab (arrow) and the other set is on the right platform. The lamps are green and red. The lamps inform the loader operator of the loading progress toward a target payload weight (set through the VIMS Keypad). The lamps are active only during the loading cycle and are off at all other times.

During loading, the green (continue loading) lamps will be ON until the payload is 95% of the target weight setting. Then, the red (stop loading) lamp will light. A "last pass" indication can be programmed into the system using the VIMS Keypad. With last pass indication, the VIMS calculates an average loader pass size and predicts payload weight. If the predicted weight after the NEXT loader pass will be above 95% of the target weight setting, the red lamps FLASH. The red lamps will be ON continuously after the last pass (when fully loaded).

A minimum of three loader passes are required for the "last pass" indication option to function correctly.

36


Shown is a view of the operator's seat and the trainer's seat. The seats are more comfortable with improved seat adjustments.

The trainer's seat has more leg room and can be replaced with an attachment air suspension seat.

37


The "C" Series truck hoist system is electronically controlled. The hoist control lever (arrow) activates the four positions of the hoist control valve. The four positions are: RAISE, HOLD, FLOAT, and LOWER.

A fifth position of the hoist valve is called the SNUB position. The operator does not have control over the SNUB position. The body position sensor (see Visual No. 129) controls the SNUB position of the hoist valve. When the body is lowered, just before the body contacts the frame, the Transmission/Chassis ECM signals the hoist solenoids to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent hard contact of the body with the frame.

The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist valve will actually be in the SNUB position.

If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until:

1. The hoist lever is moved into the HOLD or FLOAT position; and2. the shift lever has been cycled into and out of NEUTRAL.

NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, the lever must be moved into HOLD and then FLOAT before the body will lower.

38


Shown is an overall view of the dash from the left side of the cab. Some of the improvements are:

- Telescopic/tilt steering column for individual adjustment- Intermittent wiper/washer, turn signal control and dimmer switch- Enhanced instrument layout- Backlit rocker switches- Steering wheel mounted electric horn control

39


The operator controls to the left of the steering column are:

- Telescopic/tilt steering column adjustment lever (1): Push for telescoping and pull for tilt- Intermittent wiper/washer, turn signal control and dimmer switch (2)- Steering wheel mounted electric horn control (3)- Cigarette lighter (4): The cigarette lighter socket receives a 12-Volt power supply. This

socket can be used as a power supply for 12-Volt appliances. Another 12-Volt power port is provided behind the operator's seat.

40


1

2

3

4

Shown is a closer view of the intermittent wiper/washer, turn signal control and dimmer switch.

Windshield washer: Push the button at the end of the lever to activate the electrically powered windshield washer.

Intermittent wiper switch (six positions):

- OFF (0)- Intermittent position 1 (one bar)- Intermittent position 2 (two bars)- Intermittent position 3 (three bars)- Low speed continuous wiper (I)- High speed continuous wiper (II)

Dimmer switch: Pull the lever toward the operator for BRIGHT lights, and push the lever away from the operator for DIM lights.

Turn signals: Lift the lever for a RIGHT turn, and lower the lever for a LEFT turn.

41


Located on the right side of the steering column is the manual retarder lever. The manual retarder lever is used to modulate engagement of the service brakes on all four wheels. The retarder system allows the machine to maintain a constant speed on long downgrades. The retarder will not apply all of the normal braking capacity.

Located on the dash to the right of the retarder lever are (from left to right):

- Key start switch- Temperature variable knob- Fan speed switch

NOTICEDo not use the retarder control as a parking brake or to stop the machine.

42


Located on the floor of the cab are:

- Secondary brake pedal (1): Used to modulate application of the parking brakes on all four wheels.

- Service brake pedal (2): Used to modulate engagement of the service brakes on all four wheels. For more precise modulation of the service brakes, use the manual retarder lever on the right side of the steering column.

- Throttle pedal (3): A throttle position sensor is attached to the throttle pedal. The throttle position sensor provides the throttle position input signals to the Engine ECM.

NOTE: The throttle position must be programmed to the 10 to 90% setting. The earlier trucks must be programmed to a 10 to 50% throttle position. The setting is changed in the Engine ECM configuration screen with ET.

The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolant temperature is below 60°C (140°F). The rpm is gradually reduced to 1000 rpm between 60°C (140°F) and 71°C (160°F). When the temperature is above 71°C (160°F), the engine will idle at LOW IDLE (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or depress the throttle momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes.

43


1

23

To the right of the operator's seat is the shift console. Located on the shift console are the transmission shift lever (1) and the parking brake air valve (2).

The "C" Series truck transmissions have SIX speeds FORWARD and ONE speed REVERSE. The top gear limit and body up gear limit are programmable through the Transmission/Chassis ECM. The top gear limit can be changed from THIRD to SIXTH. The body up gear limit can be changed from FIRST to THIRD.

44


1

2

Located in the overhead panel are several switches:

- Hazard lights (1)

- Headlights and parking/taillights (2)

- Fog lights (3)

- Back-up lights (4)

- Front flood/ladder lights (5)

45


1 2 3 4 5

Shown is the circuit breaker panel located behind the operator's seat. The previous "B" Series trucks used fuses to protect many of the electrical circuits. The "C" Series trucks use only circuit breakers to protect the electrical circuits.

A 12-Volt/5 amp power port (1) provides a power supply for 12-Volt appliances, such as a laptop computer.

A laptop computer with the VIMS software installed can be connected to the diagnostic connector (2) to obtain diagnostic and production information from the VIMS Electronic Control.

A laptop computer with the Electronic Technician (ET) software installed can be connected to the CAT Data Link connector (3) to obtain diagnostic information and perform programming functions on all the electronic controls.

46


1

2

3

Shown is the center of the front dash panel. Eight dash indicators, the four-gauge cluster module, and the speedometer/tachometer module are visible.

The four dash indicators to the left of the four-gauge cluster module are (from top to bottom):

- Left turn

- Body up: Lights when the body is up. Input is from the body position sensor.

- Reverse: Lights when the shift lever switch is in REVERSE.

- High beam

The four dash indicators to the right of the speedometer/tachometer module are (from top to bottom):

- Right turn

- Action lamp: Lights when a Category 2, 2-S, or Category 3 Warning is active.

- Retarder: Lights when the retarder is ENGAGED (Auto or Manual). Flashes rapidly when a fault in the ARC system is detected.

- TCS: Lights when the Traction Control System (TCS) is ENGAGED.

47


The four systems monitored by the four-gauge cluster module are (top and bottom, left to right):

- Engine coolant temperature: Maximum operating temperature is 107° C (225° F).

- Brake oil temperature: Maximum operating temperature is 121° C (250° F).

- System air pressure: Minimum operating pressure is 450 kPa (65 psi).

- Fuel level: Minimum operating levels are 15% (Category 1) and 10% (Category 2).

The three systems monitored by the speedometer/tachometer module are:

- Tachometer: Displays the engine speed in rpm.

- Ground speed: Displayed in the left side of the three-digit display area and can be displayed in miles per hour (mph) or kilometers per hour (km/h).

- Actual gear: Displayed in the right side of the three-digit display area and consists of two digits that show the actual transmission gear that is engaged. The left digit shows the actual gear (such as "1," "2," etc.). The right digit shows the direction selected ("F," "N" or "R").


To the right of the Speedometer/Tachometer Module are several rocker switches. The rocker switches control the following systems:

Top row (from left to right)- Throttle back-up: Raises the engine speed to 1300 rpm if the throttle sensor signal is

invalid.

- Ether starting aid: Allows the operator to manually inject ether if the engine oil temperature is below 10°C (50°F) and engine speed is below 1900 rpm. The manual ether injection duration is five seconds (see Visuals No. 66 and 90).

- ARC: Activates the Automatic Retarder Control (ARC) system.

- Brake release/hoist pilot: Used to release the parking brakes for towing and provide hoist pilot oil to lower the body with a dead engine. The small latch must be pushed UP before the switch can be pushed DOWN.

- TCS test: Tests the Traction Control System (TCS). Use this switch when turning in a tight circle with the engine at LOW IDLE and the transmission in FIRST GEAR. The brakes should ENGAGE and RELEASE repeatedly. The test must be performed while turning in both directions to complete the test.

Bottom row (from left to right)- Panel Lights: Use this switch to DIM the panel lights

- Air Conditioning: Use this switch to turn ON the air conditioner.

48


Shown is the Vital Information Management System (VIMS) message center module (1) and the keypad module (2).

The message center module consists of an alert indicator, a universal gauge, and a message display window. The alert indicator flashes when a Category 1, 2, 2-S, or 3 Warning is present.

The universal gauge displays active or logged data (machine) and maintenance (system) events. The universal gauge will also display the status of a sensor parameter selected for viewing by depressing the GAUGE key on the keypad.

The message display window shows various types of text information to the operator, depending on the menu selected with the keypad. An active event will override most displays until acknowledged by depressing the OK Key.

49


1

2

The VIMS provides three Warning Categories. The first category requires only operator awareness. The second category states that the operation of the machine and the maintenance procedure of the machine must be changed. The third Warning Category states that the machine must be safely shut down immediately.

Warning Category 1

For a Category 1 Warning, the alert indicator will flash. The universal gauge may display the parameter and a message will appear in the message display window. A Category 1 Warning alerts the operator that a machine system requires attention. The "OK" key on the keypad can be used to acknowledge the warning. Some warnings will be silenced for a predetermined period. After this time period, if the abnormal condition is still present, the warning will reappear.

Warning Category 2

For a Category 2 Warning, the alert indicator and the action lamp will flash. The universal gauge may display the parameter and a message will appear in the message display window. A Category 2 warning alerts the operator that a change in machine operation is required to avoid possible damage to the indicated system. The "OK" key on the keypad can be used to acknowledge the warning. Some warnings will be silenced for a predetermined period. After this time period, if the abnormal condition is still present, the warning will reappear.

Warning Category 2-S

For a Category 2-S Warning, the alert indicator and the action lamp will flash and a continuous action alarm will sound, which indicate a SEVERE Category 2 Warning. The universal gauge may display the parameter and a message will appear in the message display window. A Category 2-S Warning alerts the operator to immediately change the operation of the machine to avoid possible damage to the indicated system. When the change in operation is made to an acceptable condition, the action alarm will turn off.

Warning Category 3

For a Category 3 Warning, the alert indicator and the action lamp will flash and the action alarm will sound intermittently. The universal gauge may display the parameter and a message will appear in the message display window. A Category 3 Warning alerts the operator that the machine must be safely shut down immediately to avoid damage to the machine or prevent personal injury. Some Category 3 Warnings cannot be stopped by pressing the "OK" key.


50

The VIMS uses two interface modules to receive input signals from many switches and sensors located around the machine. The VIMS also communicates with other electronic controls on the machine. The VIMS provides the operator and the service technician with a complete look at the current and past conditions of all the systems on the truck.

The Truck Production Management System (TPMS) is an integral part of the VIMS. Access to the TPMS information is provided through the VIMS message center and keypad modules and a laptop computer with the VIMS PC software installed.

The VIMS monitors all the systems on the truck, but ET is used for programming, running diagnostic tests and retrieving logged information from the Engine ECM, the Transmission/Chassis ECM, and the Brake ECM (ARC and TCS).


%��&��/��$

��$

��&+

$��$��

,��$��

6�)+��$��

��

7�&��"��*��$��

7�&��"��*��$��

��

7"$��%��

��*�1��

��%�#��(

��6�)��

�1��

��&+

��&

��%��/��

7�&� $��$��

#��+��)��#��(

7"$��!�.898�

��

��%�#��(

7"%��"��!$�%"��$��,�$��%��5�%�$�

:7"$�;

�+��&��/�%��&��

$��

6�)+��#��(

��(��$�:�!��/%��;

9�28 $ '�

(&/ �

Shown is the location are the Brake ECM (1) and the Transmission/Chassis ECM (2).

The Brake ECM controls the Automatic Retarder Control (ARC) system, the Traction Control System (TCS), and rear axle cooling.

The Transmission/Chassis ECM controls the shifting of the transmission, torque converter lockup, the hoist system, the neutral-start feature, power train filter and temperature monitoring, and the automatic lubrication feature.

All these electronic controls, along with the Engine ECM, communicate with each other on the CAT Data Link. All the information from these controls can be accessed through the VIMS message center or a laptop computer with Electronic Technician (ET) or VIMS PC software.

51


1

2

Shown is a laptop computer with the VIMS PC diagnostic software installed. The laptop computer is connected to the VIMS diagnostic connector.

Some of the operations that can be performed with a laptop computer with VIMS PC installed are:

- View real time data (similar to the status menu of ET)- View payload data- Start and stop a data logger- Calibrate the payload system- Upload source and configuration files (similar to flash programming other ECM’s with ET)- Assign serial and equipment numbers- Reset onboard date, time, and hourmeter- Download event list, data logger, event recorder, payload data, trend data, cumulative data,

and histogram data

INSTRUCTOR NOTE: For more detailed information on the VIMS, refer to the Service Manual Modules "Off-Highway Truck/Tractors Vital Information Management System (VIMS)--System Operation" (Form RENR2630) and "Off-Highway Truck/Tractors Vital Information Management System (VIMS)--Testing and Adjusting Troubleshooting" (Form RENR2631).

52


Shown is the 7X1700 Communication Adapter and a laptop computer with the Electronic Technician (ET) diagnostic software installed. The communication adapter is connected to the CAT Data Link diagnostic connector located on the circuit breaker panel.

The electronic controls (Transmission/Chassis ECM and Brake ECM) used on the "C" Series trucks no longer have diagnostic windows to access diagnostic information. To perform diagnostic and programming functions with these electronic controls, the service technician must use a laptop computer with ET.

53


ENGINE

Shown is the 3516B engine used in the 789C Off-highway Truck. The 789C is equipped with the Caterpillar 3516B quad turbocharged and aftercooled engine. The 785C is equipped with the Caterpillar 3512B twin turbocharged and aftercooled engine.

The 785C and 789C engines have increased horsepower.

The engine power ratings for the 785C and 789C trucks are:

785C: gross power--1082 kW (1450 hp) net power--1007 kW (1350 flywheel hp)

789C: gross power--1417 kW (1900 hp) net power--1335 kW (1790 flywheel hp)

These engines utilize the Electronic Unit Injection (EUI) system for power, reliability and economy with reduced sound levels and low emissions.

54


55

Engine Electronic Control System

Shown is the electronic control system component diagram for the 3500B engines used in the "C" Series trucks. Fuel injection is controlled by the Engine Electronic Control Module (ECM).

Many electronic signals are sent to the Engine ECM by sensors, switches, and senders. The Engine ECM analyzes these signals and determines when and for how long to energize the injector solenoids.

When the injector solenoids are energized determines the timing of the engine. How long the solenoids are energized determines the engine speed.


��

��

��

��

��

� �� !

�� "��

��

�� #��

��#�$��

%�& ��#�'"��

%�& ��%�(�

��)��

*+��'"�)��

(� ��

,��

�"��# ' �&��

%�& �� -�. ��!

��

# ' �&��

%��

$ ��

�/+00)�%�%�#��12��1#��3�#%(��(��1%1#�$2��(

�

%�� -� ��2�4��

#�� )��!

� &��#��2��

��'�"��

%�& �� !

#��

%�& ��

��

��.��#�'"��

��.��#��2��

� &��#��%5��

��.��#��%5��

#��

(��%��

#��' �� %�(

)��%�(

62(�

78�6

"Pull-up voltage" is a voltage supplied from within an ECM through an internal resister which "pulls up" the signal circuit contact on the connector of the control input. Pull-up circuits are used on most sensor and switch inputs of electronic controls. Frequency sensors do not receive a pull-up voltage (except for suspension cylinder pressure sensors). The pull-up voltage is determined by the ECM design and will vary between ECMs. Pull-up voltage sometimes is the same value as the voltage source that powers the sensor, but does not have to be. Remember, pull-up voltage is on the SIGNAL input to the ECM for a given sensor (or switch) and most often HAS NO relationship to the voltage that POWERS the sensor. PWM sensors most often have a pull-up voltage value DIFFERENT than the voltage that powers them. Analog sensors, as used with the engine ECM, most often have a pull-up voltage that is the SAME as the voltage that powers them. The Engine ECM will provide a "pull-up voltage" to the signal circuit of the sensors when the ECM senses an OPEN circuit. The signal circuit is pin C of the 3-pin sensor connectors. The pull-up voltage for the Engine ECM sensors is approximately 6.50 volts.

To test for pull-up voltage, use a digital multimeter set to DC voltage, and use the following procedure (key start switch must be ON):

1. Measure between pins B (analog or digital return) and C (signal) on the ECM side of a sensor connector before it is disconnected. The voltage that is associated with the current temperature or pressure should be shown.

2. Disconnect the sensor connector while still measuring the voltage between pins B and C. If the circuit between the ECM and the sensor connector is good, the multimeter will display the pull-up voltage.


Fuel injection and some other systems are controlled by the Engine ECM (arrow) located on top of the engine. Other systems controlled by the Engine ECM include:

- Ether injection - Engine start function- Engine oil pre-lubrication - Variable speed fan control

The Engine ECM has two 40-pin connectors. The connectors are identified as "J1" and "J2." Be sure to identify which connector is the J1 or J2 connector before performing diagnostic tests.

The Engine ECM is cooled by fuel. Fuel flows from the fuel transfer pump through the ECM to the secondary fuel filters.

Occasionally, Caterpillar will make changes to the internal software (personality module) that controls the performance of the engine. These changes can be performed by physically installing a new personality module, located below the ECM, or by using the WinFlash program that is part of the laptop software program, Electronic Technician (ET). ET is used to diagnose and program the electronic controls used in Off-highway Trucks. If using the WinFlash program, a "flash" file must be obtained from Caterpillar and uploaded into the existing ECM personality module.

The ECM in earlier 3500 engines had one 70-pin connector and cannot be reprogrammed with the WinFlash application in ET. Reprogramming of the earlier ECM requires a replacement of the personality module located behind an access cover on the ECM.

56


A timing calibration connector is located next to the ECM. If the engine requires timing calibration, a timing calibration sensor (magnetic pickup) is installed in the flywheel housing and connected to the timing calibration connector.

Using the Caterpillar ET service tool, timing calibration is performed automatically for the speed/timing sensors. The desired engine speed is set to 800 rpm. This step is performed to avoid instability and ensures that no backlash is present in the timing gears during the calibration process.

Timing calibration improves fuel injection accuracy by correcting for any slight tolerances between the crankshaft, timing gears, and timing wheel.

Timing calibration is normally performed after the following procedures:

1. ECM replacement2. Speed/timing sensor replacement3. Timing wheel replacement

INSTRUCTOR NOTE: Some of the engine electronic control system input components are shown during the discussion of other systems. See the following visual numbers:

23. Engine oil level switch25. Engine shutdown switch46. CAT Data Link connector48. Throttle back-up switch48. Manual ether switch62. Air conditioner compressor pressure switch63. Engine crankcase pressure sensor68. Coolant temperature sensor68. Turbocharger outlet pressure sensor68. Engine fan speed sensor74. Coolant flow switch78. Rear aftercooler temperature sensor81. Engine oil pressure and filter restriction sensors86. Fuel filter restriction switch90. Turbocharger inlet pressure sensor92. Turbocharger temperature sensor


The atmospheric pressure sensor (arrow) is located adjacent to the Engine ECM. The Engine ECM uses the atmospheric pressure sensor as a reference for calculating boost and air filter restriction.

The sensor is also used for derating the engine at high altitudes. The ECM will derate the engine at a rate of 1% per kPa to a maximum of 20%. Derating begins at a specific elevation. The elevation specification can be found in the Technical Marketing Information (TMI) located on the Caterpillar Network. If the Engine ECM detects an atmospheric pressure sensor fault, the ECM will derate the fuel delivery to 20%. If the Engine ECM detects an atmospheric and turbocharger inlet pressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of 40%.

The Engine ECM also uses the atmospheric pressure sensor as a reference when calibrating all the pressure sensors.

The atmospheric pressure sensor is one of the many analog sensors that receive a regulated 5.0 ± 0.5 Volts from the Engine ECM. The atmospheric pressure sensor output signal is a DC Voltage output signal that varies between 0.2 and 4.8 Volts DC with an operating pressure range between 0 and 111 kPa (0 and 15.7 psi).

To check the output signal of analog sensors, connect a multimeter between Pins B and C of the sensor connector. Set the meter to read "DC Volts." The DC Voltage output of the atmospheric pressure sensor should be between 0.2 and 4.8 Volts DC.

57


The engine speed/timing sensor (1) is positioned near the rear of the left camshaft. The sensor signals the speed, direction, and position of the camshaft by counting the teeth and measuring the gaps between the teeth on the timing wheel which is mounted on the camshaft.

The engine speed/timing sensor is one of the most important inputs to the Engine ECM. If the Engine ECM does not receive an input signal from the engine speed/timing sensor, the engine will not run.

The engine speed/timing sensor receives a regulated 12.5 ± 1.0 Volts from the Engine ECM. To check the output signal of the speed/timing sensor, connect a multimeter between Pins B and C of the speed/timing sensor connector. Set the meter to read "Frequency." The frequency output of the speed/timing sensor should be approximately:

- Cranking: 23 to 40 Hz- Low Idle: 140 Hz- High Idle: 385 Hz

A passive (two wire) engine speed sensor (2) is positioned on top of the flywheel housing. The passive speed sensor uses the passing teeth of the flywheel to provide a frequency output. The passive speed sensor sends the engine speed signal to the Transmission/Chassis ECM and the Brake ECM.

58


1

2

The signal from the passive speed sensor is used for several purposes:

- Automatic Retarder Control (ARC) engine control speed- Shift time calculations- Transmission Output Speed (TOS) ratification

The output signal of the passive speed sensor can also be checked by connecting a multimeter between the two pins of the speed sensor connector and setting the meter to read frequency.

NOTE: Turn ON the engine shutdown switch (see Visual No. 25) during the cranking test to prevent the engine from starting. The cranking speed and frequency output will vary depending on weather and machine conditions. When viewing engine speed in the ET status screen, cranking speed should be between 100 and 250 rpm.


The throttle position sensor (arrow) provides the desired throttle position to the Engine ECM. If the Engine ECM detects a fault in the throttle position sensor, the throttle back-up switch (see Visual No. 48) can be used to increase the engine speed to 1300 rpm.

The throttle position sensor receives a regulated 8.0 ± 0.5 Volts from the Engine ECM. The throttle position sensor output signal is a Pulse Width Modulated (PWM) signal that varies with throttle position and is expressed as a percentage between 0 and 100%.

To check the output signal of the throttle position sensor, connect a multimeter between Pins B and C of the throttle position sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the throttle position sensor should be:

- Low Idle: 16 ± 6%- High Idle: 85 ± 4%

NOTE: The throttle position must be programmed to the 10 to 90% setting. The earlier trucks must be programmed to a 10 to 50% throttle position. The setting is changed in the Engine ECM configuration screen with ET.

59


Shown is the top of a cylinder head with the valve cover removed. The most important output from the Engine ECM is the Electronic Unit Injection (EUI) injector solenoid (arrow). One injector is located in each cylinder head. The engine control analyzes all the inputs and sends a signal to the injector solenoid to control engine timing and speed.

Engine timing is determined by controlling the start and end time that the injector solenoid is energized. Engine speed is determined by controlling the duration that the injector solenoid is energized.

3500B injectors are calibrated during manufacturing for precise injection timing and fuel discharge. After the calibration, a four-digit "E-trim" code number is etched on the injector tappet surface. The E-trim code identifies the injector’s performance range.

When the injectors are installed into an engine, the trim code number of each injector is entered into the personality module (software) of the Engine ECM using the ECAP or ET service tool. The software uses the trim code to compensate for the manufacturing variations in the injectors and allows each injector to perform as a nominal injector.

When an injector is serviced, the new injector’s trim code should be programmed into the Engine ECM. If the new trim code is not entered, the previous injector’s characteristics are used. The engine will not be harmed if the new code is not entered, but the engine will not provide peak performance.

60


61

The 3500B engines have many improvements over the original 3500 engines. Some of the improvements are accomplished by adding additional switch and sensor inputs to the Engine ECM. Adding additional inputs allows the ECM to control the engine more precisely. Additional inputs to the 3500B ECM are:

- Coolant flow is monitored (see Visual No. 74).- Rear aftercooler temperature is measured (see Visual No. 78).- Engine oil level is monitored (see Visual No. 23).- Two turbocharger temperature sensors measure exhaust temperatures (see Visual No. 92).- Two engine oil pressure sensors are located on the oil filter base to measure oil pressure

and oil filter restriction (see Visual No. 81.- Engine fan speed is measured (with variable fan speed attachment).- Fuel filter restriction is monitored (see Visual No. 86).- Air conditioner compressor pressure is monitored (for variable fan speed control) (see

Visual No. 62).- Engine crankcase pressure is measured (see Visual No. 63).


/+00)�2(��6%(%1#�21�-#��92#�:%��1$��%1��

��

��.��#�'"��

��%�& ��

��#��&��#�'"��

��%�& ��

��%�& ��"��

��

�� '"��

��

An air conditioner compressor switch (arrow) is located at the rear of the air conditioner compressor. If the truck is equipped with the variable fan speed attachment, the air conditioner compressor switch signals the Engine ECM when the air conditioner system is ON. When the air conditioner system is ON, the ECM sets the variable speed fan at MAXIMUM rpm.

Disconnecting the air conditioner compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm.

62


The crankcase pressure sensor (arrow) is located on the right side of the engine above the engine oil cooler. The crankcase pressure sensor provides an input signal to the Engine ECM. The ECM provides the signal to the VIMS, which informs the operator of the crankcase pressure.

High crankcase pressure may be caused by worn piston rings or cylinder liners.

If crankcase pressure exceeds 3.6 kPa (.5 psi) or 14.4 inches of water, a high crankcase pressure event will be logged. No factory password is required to clear this event.

63


64

The 3500B ECM logs the four events of the previous 3500 engine plus some additional events. The four events logged by the 3500 ECM and the 3500B ECM are:

Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%.

If the atmospheric and turbo inlet pressure sensors both fail at the same time, a derate of 40% will occur.

Low oil pressure: From less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE.

High coolant temperature: Greater than 107° C (226° F).

Engine overspeed: Greater than 2200 rpm.

NOTE: Factory passwords are required to clear all the events listed above.


/+00)�2(��6%(%1#��%62�-��%$�%6%1#�

��

��

��: &��#�'"��

��%�& ��"��

65

Additional events logged by the 3500B ECM are:

Oil filter restriction: Greater than 70 kPa (10 psi), no factory password required. Greater than 200 kPa (29 psi), factory password required.

Fuel filter restriction: Greater than 138 kPa (20 psi). No factory password required.

Exhaust temperature high: Greater than 750° C (1382° F). Maximum derate of 20%. Factory password required.

Aftercooler coolant temperature high: Greater than 107° C (226° F). Factory password required.

Engine oil level low: No factory password required.

Crankcase pressure high: Greater than 3.6 kPa (.5 psi) or 14.4 inches of water. No factory password required.


/+00)�2(��6%(%1#��$$2#2�1��%$�%6%1#�

��

�

�� -��$�. ��

�

��: &��%5��#�'"�� )��

�

��: &��.��#�'"�� : &��)��

�

��%�& ��

�

��: &��

Coolant flow low: Factory password required.

User defined shutdown: The customer has the option of installing systems (fire suppression) that will shut down the engine if desired. If the installed system sends a ground signal to the Engine ECM at Connector J1 Pin 19, a user defined shutdown will occur. Factory password required.

The VIMS will shut down the engine for any of the following conditions:- Engine oil level low- Engine oil pressure low- Engine coolant temperature high- Engine coolant level low- Aftercooler coolant level low

The engine will only shutdown when ground speed is 0 and the parking brake is ENGAGED. The Engine ECM does not log events for VIMS initiated engine shutdowns.

Pre-lube override: Override the engine oil pre-lubrication system with the key start switch. Factory password required. (see Visual No. 67)


66

The Engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the ECM are:

Ether Injection: The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 48). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10° C (50° F) and engine speed is below 1900 rpm.

Radiator Shutter Control (attachment): On trucks that operate in cold weather, shutters can be added in front of the radiator. Installing shutters in front of the radiator allows the engine to warm up to operating temperature quicker. If a truck is equipped with the attachment radiator shutter control, the shutters are controlled by the Engine ECM.


/+00)�2(��6%(%1#��3�#%(��1#��%$�)3�%�(

��%��2�4��

��

��(��

��

��%�& ��

��%�& ��

��6�� "��

��%�& �� '

Cool Engine Elevated Idle: The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolant temperature is below 60° C (140° F). The rpm is gradually reduced to 1000 rpm between 60° C (140° F) and 71° C (160° F). When the temperature is greater than 71° C (160° F), the engine will operate at low idle (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or depress the throttle momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes.

Cold Cylinder Cutout: The 3500B engine uses a cold cylinder cutout function to:- Reduce white exhaust smoke (unburned fuel) after start-up and during extended idling in

cold weather- Minimize the time in Cold Mode- Reduce the use of ether injection.

After the engine is started and the automatic ether injection system has stopped injecting ether, the Engine ECM will cut out one cylinder at a time to determine which cylinders are firing. The ECM will disable some of the cylinders that are not firing.

The ECM can identify a cylinder which is not firing by monitoring the fuel rate and engine speed during a cylinder cutout. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cutout to determine if the cylinder is firing.

Disabling some of the cylinders during Cold Mode operation will cause the engine to run rough until the coolant temperature increases above the Cold Mode temperature. This condition is normal, but the operator should be aware it exists to prevent unnecessary complaints.

Engine Start Function: The Engine Start function is controlled by the Engine ECM and the Transmission/Chassis ECM. The Engine ECM provides signals to the Transmission/Chassis ECM regarding the engine speed and the condition of the engine pre-lubrication system. The Transmission/Chassis ECM will energize the starter relay only when:

- The shift lever is in NEUTRAL.- The parking brake is ENGAGED.- The engine speed is zero rpm.- The engine pre-lubrication cycle is complete or turned OFF.

NOTE: To protect the starter, the starter is disengaged when the engine rpm is above 300 rpm.


Engine Oil Pre-lubrication (attachment): Engine oil pre-lubrication is controlled by the Engine ECM and Transmission/Chassis ECM. The Engine ECM energizes the pre-lubrication pump relay located behind the cab (see Visual No. 53) The relay behind the cab then energizes the pre-lube relay (1) on the front engine mount. The Engine ECM signals the Transmission/Chassis ECM to crank the engine when:

- Engine oil pressure is 3 kPa (.4 psi) or higher.- The pre-lubrication pump (2) has run for 17 seconds. (If the system times out after 17

seconds, a pre-lubrication time out fault is logged in the Engine ECM.)- The engine has been running in the last two minutes.- Coolant temperature is above 50° C (122° F).

The engine oil pre-lubrication system can be bypassed to allow quick starts. To override the pre-lubrication system, turn the key start switch to the CRANK position for a minimum of two seconds. The Transmission/Chassis ECM will begin the pre-lube cycle. While the pre-lube cycle is active, turn the key start switch to the OFF position. Within 10 seconds, turn the key start switch back to the CRANK position. The Transmission/Chassis ECM will energize the starter relay.

If the engine oil pre-lubrication system is bypassed using the above procedure, the Engine ECM will log a pre-lube override event that requires a factory password to clear.

NOTE: The ECAP and ET can enable or disable the pre-lubrication feature in the Engine ECM.

67


1 2

Variable Speed Fan Control (attachment): If the engine is equipped with a variable speed fan, the Engine ECM regulates the fan speed. Fan speed varies according to the temperature of the engine. The ECM sends a signal to the variable speed fan control solenoid valve (1) and engine oil pressure engages a clutch as needed to change the speed of the fan.

The jacket water coolant temperature sensor (2) is located in the jacket water temperature regulator (thermostat) housing. The ECM uses the coolant temperature sensor information as the main parameter to control the fan speed. The aftercooler temperature sensor, air conditioner pressure sensor and brake cooling oil temperature sensors are also used as inputs to determine the required fan speed. A speed sensor (not shown) is located behind the fan pulley and informs the ECM of the current fan speed.

The variable speed fan feature can be turned off using the ECAP or ET service tool. Turning off the variable speed fan feature will set the fan speed at MAXIMUM rpm. Disconnecting the air conditioning compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm (see Visual No. 62).

The turbocharger outlet pressure sensor (3) sends an input signal to the Engine ECM. The ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure.

INSTRUCTOR NOTE: For more information on the variable speed fan, refer to the Service Manual "Variable Speed Fan Clutch" (Form SENR8603).

68


1

2

3

Engine Oil Renewal System (attachment): Located on the right side of the engine are the components of the engine oil renewal system. Engine oil flows from the engine block to the engine oil renewal solenoid valve (arrow). When the solenoid is energized and de-energized, a small amount of oil flows from the engine oil renewal solenoid valve into the fuel line that returns to the fuel tank. The engine oil mixes with the fuel in the tank and flows with the fuel to the EUI injectors to be burned.

If the machine is equipped with the engine oil renewal system, the engine oil filters, the engine oil renewal system filter, the primary fuel filter, and the secondary fuel filters must all be changed at 500 hour intervals. The engine oil should be changed at least once per year or 4000 service meter hours.

Engine oil samples must be taken regularly to ensure that the soot level of the engine oil is in a safe operating range.

69


The Engine ECM regulates the amount of oil that is injected by the engine oil renewal solenoid valve. Several parameters must be met before the ECM will allow the injection of oil through the engine oil renewal system. The parameters that must be met are:

- Fuel position is greater than 10.- Engine rpm is between 1100 and 1850 rpm.- Jacket water temperature is between 63° C (145° F) and 107° C (225° F).- Fuel filter differential pressure is less than 140 kPa (20 psi).- Fuel level is greater than 10%.- Engine oil level switches are sending a valid signal to the Engine ECM.- Engine has been running more than five minutes.

The engine oil renewal system can be turned ON or OFF with the ET service tool. The amount of oil injected can also be adjusted by programming the Engine ECM with the ET service tool. The factory setting shown in the service tool is "0" and is equivalent to a 0.5% oil to fuel ratio. The ratio can be changed with the service tool from minus 50 (-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuel ratios.

INSTRUCTOR NOTE: For more detailed information on servicing the oil renewal system, refer to the Service Manual Module "Oil Renewal System" (Form RENR2223).


70

Shown is a sectional view of the engine oil renewal solenoid valve. When the Engine Slave ECM determines that oil can be injected into the fuel return line, a Pulse Width Modulated (PWM) duty cycle signal is sent to the oil renewal solenoid. The solenoid is turned ON for 1.25 seconds and turned OFF for 1.25 seconds for a total cycle time of 2.5 seconds. How many times the solenoid is turned ON and OFF will determine the volume of oil that is injected. Oil is injected when the solenoid is turned ON and oil is also injected when the solenoid is turned OFF. When the solenoid is turned ON, engine oil flows to the left side of the piston and pushes the piston to the right. The volume of oil that is trapped between the right side of the piston and the check ball compresses the spring and opens the passage to the fuel return line. When the solenoid is turned OFF, engine oil flows to the right side of the piston and pushes the piston to the left. The volume of oil that is trapped between the left side of the piston and the check ball compresses the spring and opens the passage to the fuel return line. The volume of delivery is equal to 3.04 ml/cycle (0.1 oz/cycle).


�1

� ��

#��

��'�%�& ��

��

� ��

��'�%�& ��

�2��%1%9��%1�2$�6��6%

#��

Cooling System

Shown is a 789C truck. The capacity of the 789C cooling system has been increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.). The radiator is larger and a shunt tank (1) has been added above the radiator. The shunt tank provides a positive pressure at the coolant pump inlets to prevent cavitation during high flow conditions.

The cooling system is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. The only connection between these two systems is a small hole in the separator plate in the shunt tank. The small hole in the shunt tank prevents a reduction of coolant from either of the two systems if leakage occurs in one of the separator plates in the radiator top or bottom tank. When servicing the cooling systems, be sure to drain and fill both systems separately.

The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the coolant level.

A coolant level switch (3) is located on each side of the shunt tank to monitor the coolant level of both cooling systems (guard removed for viewing switch). The coolant level switches provide input signals to the VIMS, which informs the operator of the engine coolant levels.

The jacket water and the aftercooler cooling systems each have their own relief valve (4). If a cooling system overheats or if coolant is leaking from a relief valve, clean or replace the relief valve.

71


1

2

3

4

Shown is the radiator on an earlier 785C. The earlier 785C did not have a shunt tank. The coolant levels are checked at the radiator top tank. Use the gauges (1) on the top tank to check the coolant level.

Two coolant level switches (2) are located on the top tank to monitor the coolant level of both cooling systems. The coolant level switches provide input signals to the VIMS, which informs the operator of the engine coolant levels.

Pressure relief valves (3) prevent the cooling systems from becoming over pressurized.

The jacket water cooling system uses the cores on the right side of the radiator (approximately 60% of the total capacity). The jacket water cooling system temperature is controlled by temperature regulators (thermostats).

The aftercooler cooling system uses the cores on the left side of the radiator (approximately 40% of the total capacity). The aftercooler cooling system does not have thermostats in the circuit. The coolant flows through the radiator at all times to keep the turbocharged inlet air cool for increased horsepower.

72


1

2

3

The jacket water pump (1) is located on the right side of the engine. The pump draws coolant from the bypass tube (2) until the temperature regulators (thermostats) open. The thermostats are located in the housing (3) at the top of the bypass tube. When the thermostats are open, coolant flows through the radiator to the water pump inlet.

If the jacket water cooling system temperature increases above 107° C (226° F), the Engine ECM will log an event that requires a factory password to clear.

73


1

2

3

Coolant flows from the jacket water pump, past the coolant flow warning switch (1), and through the various system oil coolers (engine, torque converter/transmission and rear brake).

The coolant flow switch sends an input signal to the Engine ECM. The Engine ECM provides the input signal to the VIMS, which informs the operator of the coolant flow status.

If the ECM detects a low coolant flow condition, a low coolant flow event will be logged. A factory password is required to clear this event.

Jacket water coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (2).

74


1

2

Shown is the right side of the engine. The engine oil cooler (1) and the rear brake oil coolers (2) are visible in this view. Jacket water coolant flows through these coolers and through the tube (3) to the transmission oil cooler.

Jacket water coolant flows through the transmission oil cooler, the engine oil cooler and the rear brake oil coolers to both sides of the engine cylinder block. Coolant flows through the engine block and through the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).

75


1

2 3

76

Shown is the jacket water cooling circuit. Coolant flows from the jacket water pump through the coolers to the engine block. Coolant flows through the engine block and the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators (thermostats) and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).

The shunt tank (789C only) increases the cooling capacity and provides a positive pressure at the coolant pump inlet to prevent cavitation during high flow conditions.

In this illustration and those that follow, the colors used to identify the various pressures in the systems are:

Red - Supply oil/water pressureGreen - Drain or tank oil/waterRed and White Stripes - Reduced supply oil pressureBrown - Lubrication or cooling pressureOrange - Pilot or load sensing signal pressureBlue - Blocked oilYellow - Moving componentsPurple - Air pressure


#��' ��

%�& ��

:� �;��)��

<��,%#�9�#%��1#��9 #��'��:� �&

��

<��9��'"

��#��

:� �;��)��

%�& ��)��

The auxiliary (aftercooler) water pump (1) for the aftercooler cooling system is located on the left side of the engine. Coolant enters the aftercooler water pump from the radiator or the shunt tank supply tube (2) on the 789C truck. Coolant flows from the pump to the aftercooler cores through the large tube (3)

Aftercooler coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (not shown) located on the pump.

77


1

2

3

Located in a tube at the rear of the aftercooler is the rear aftercooler temperature sensor (1). The rear aftercooler temperature sensor provides an input signal to the Engine ECM. The Engine ECM uses the rear aftercooler temperature sensor signal with the jacket water temperature sensor signal, the brake temperature sensor signals (four) and the air conditioner compressor pressure signal to control the variable speed fan attachment.

The Engine ECM also provides the input signal to the VIMS, which informs the operator of the aftercooler coolant temperature. If the rear aftercooler temperature increases above 107° C (226° F), the Engine ECM will log an event that requires a factory password to clear.

Coolant flows through the aftercooler cores to the front brake oil cooler (2) located at the rear of the engine.

Coolant flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit.

When the service or retarder brakes are ENGAGED, the front brake oil cooler diverter valve (3) allows brake cooling oil to flow through the front brake oil cooler.

Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

78


1

2

3

79

Shown is the aftercooler cooling circuit. Coolant flows from the aftercooler water pump through the aftercooler.

Coolant flows through the aftercooler core to the front brake oil cooler located at the rear of the engine.

Coolant then flows through the front brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling circuit does not have temperature regulators (thermostats) in the circuit.

The shunt tank increases the cooling capacity and provides a positive pressure at the aftercooler water pump inlet to prevent cavitation during high flow conditions.

The earlier 785C truck does not have a shunt tank.


��

�.��9��'"

� ��'"��

��)��

$ ��6��

��#��

�.��

��#%��%��1#��9

Lubrication System

Shown is the 3512B engine used in the 785C truck. The engine oil pump is located behind the jacket water pump on the right side of the engine. The pump draws oil from the oil pan through a screen. The relief valve (1) for the lubrication system is located on the pump.

The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump.

Oil flows from the pump through an engine oil cooler bypass valve (2) to the engine oil cooler (3). The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged.

On the 3512B engine used in the 785C truck, engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).

80


1

2

3

4

Oil flows from the engine oil cooler to the oil filters on the left side of the engine. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.

Engine oil is added at the fill tube (1) and checked with the dipstick (2). A bypass valve for each filter is located in each oil filter base. Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3) (789C only). (See Visual No. 80 for the 785C S•O•S tap location.)

The engine has two oil pressure sensors. One sensor is located on each end of the oil filter base. The front sensor measures engine oil pressure before the filters. The rear sensor (4) measures oil pressure after the filters. The sensors send input signals to the Engine ECM. The ECM provides the input signal to the VIMS, which informs the operator of the engine oil pressure. Used together, the two engine oil pressure sensors inform the operator if the engine oil filters are restricted.

If the engine oil pressure is less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE, the Engine ECM will log an event that requires a factory password to clear.

If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filter restriction event will be logged. No factory password is required to clear this event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oil filter restriction event will be logged. A factory password is required to clear this event.

81


1

2

3

4

Shown is the 3512B engine used in the 785C truck. The 3512B engine uses three oil filters located on the left side of the engine. The 3512B engine also has a fitting (arrow) that can be used to drain the engine oil trapped above the filters. Do not add oil through the fitting (arrow) because unfiltered oil will enter the engine. Any contamination could cause damage to the engine.

NOTICEWhen changing the engine oil filters, drain the engine oil trapped above the oil filters through the fitting (arrow) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine.

82


83

The engine oil pump draws oil from the oil pan through a screen.

The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump.

Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged.

Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.

Some trucks are equipped with the optional engine oil renewal system. Engine oil flows from the engine block to an engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel (see Visuals No. 69 and 70).


%1�21%��2��3�#%(

%�& ��

� ��

%�& ��

� ��

%�& ��

� ��'"

)�"��

6��

%�& ��

� ��

��'��

#��

#��

��&��

�'"

Fuel System

The fuel tank is located on the left side of the truck. Fuel is pulled from the tank through the fuel heater (not shown), if equipped, and through the primary fuel filter (1) by the fuel transfer pump located on the right side of the engine behind the engine oil pump.

A fuel level sensor (2) is also located on the fuel tank. The fuel level sensor emits an ultrasonic signal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonic signal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signal changes as the fuel level changes. The fuel level sensor provides the input signals to the VIMS, which informs the operator of the fuel level. A category level 1 warning (FUEL LVL LO) is shown on the VIMS display if the fuel level is less than 15%. A category level 2 warning (FUEL LVL LO ADD FUEL NOW) is shown on the VIMS display if the fuel level is less than 10%.

The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of the sensor, connect a multimeter between Pins 1 and 2 of the sensor connector. Set the meter to read "DC Volts."

The fuel level sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the fuel level. To check the output signal of the fuel level sensor, connect a multimeter between Pins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depth and 84% at 2000 mm (78.8 in.) of fuel depth.

84


2

1

Fuel flows from the transfer pump (1) through the Engine ECM to the secondary fuel filters located on the left side of the engine.

The fuel transfer pump contains a bypass valve (2) to protect the fuel system components from excessive pressure. The bypass valve setting is 860 kPa (125 psi), which is higher than the setting of the fuel pressure regulator.

85


1

2

The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed.

Fuel filter restriction is monitored with a fuel filter bypass switch (2) located on the fuel filter base. The fuel filter bypass switch provides an input signal to the Engine ECM. The ECM provides a signal to the VIMS, which informs the operator if the secondary fuel filters are restricted.

If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. No factory password is required to clear this event.

Fuel flows from the fuel filter base through the Electronic Unit Injection (EUI) fuel injectors (see Visual No. 60), the fuel pressure regulator, and then returns to the fuel tank. The injectors receive 4 1/2 times the amount of fuel needed for injection. The extra fuel is used for cooling.


86


12

Fuel flows from the fuel filter base through the steel tubes (1) to the EUI fuel injectors. Return fuel from the injectors flows through the fuel pressure regulator (2) before returning to the fuel tank. Fuel pressure is controlled by the fuel pressure regulator.

Fuel pressure should be 482 + 138 - 103 kPa (70 + 20 - 15 psi) at Full Load rpm.

87


1 2

88

Fuel is pulled from the tank through a fuel heater, if equipped, and sent through the primary fuel filter by the fuel transfer pump. Fuel flows from the transfer pump through the Engine ECM to the secondary fuel filters.

Fuel flows from the fuel filter base through the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator before returning through the fuel heater to the tank.

If equipped with the engine oil renewal system, engine oil flows from the engine block to the engine oil renewal system manifold. A small amount of oil flows from the engine oil renewal system manifold into the return side of the fuel pressure regulator. The engine oil returns to the fuel tank with the return fuel.

The engine oil mixes with the fuel in the tank and flows with the fuel to the injectors to be burned.


�-%��3�#%(

��#��

��#��.��'"

�� '��

��

�� :��

�� :��

��&��

%�& ��%�'

�� ' �&��'"

��:��

%�& ��)��

%�& ��

Air Induction and Exhaust System

The engine receives clean air through the air filters located on the front of the truck (789C) or on either side of the engine (785C). Any restriction caused by plugged filters can be checked at the filter restriction indicators (1). If the yellow piston is in the red zone, the filters must be cleaned or replaced.

Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. The dust valve is OPEN when the engine is OFF and closes when the engine is running. The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the air filters will have a shortened life. Replace the rubber dust valve if it becomes hard and not flexible.

The VIMS will also provide the operator with an air filter restriction warning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filter restriction.

Two filter elements are installed in the filter housings. The large element is the primary element and the small element is the secondary element.

89


1

2

The turbocharger inlet pressure sensor (1) is located in a tube between the air filters and the turbochargers. The Engine ECM uses the turbocharger inlet pressure sensor in combination with the atmospheric pressure sensor to determine air filter restriction. The ECM provides the input signal to the VIMS, which informs the operator of the air filter restriction.

If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filter restriction event will be logged, and the ECM will derate the fuel delivery (maximum derating of 20%) to prevent excessive exhaust temperatures. A factory password is required to clear this event. If the Engine ECM detects a turbocharger inlet pressure sensor fault, the ECM will derate the engine to the maximum rate of 20%. If the Engine ECM detects a turbocharger inlet and atmospheric pressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of 40%.

The Engine ECM will automatically inject ether from the ether cylinders (2) during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 48). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10° C (50° F) and engine speed is below 1900 rpm.

90


12

Shown is the 3516B engine used in the 789C truck. The 3516B engine is equipped with four turbochargers (arrows). The 785C truck has a 3512B engine with two turbochargers.

The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers.

The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercoolers. After the air is cooled by the aftercoolers, the air flows to the cylinders and combines with the fuel for combustion.

91


An exhaust temperature sensor (arrow) is located in each exhaust manifold before the turbochargers. The two exhaust temperature sensors provide input signals to the Engine ECM. The ECM provides the input signal to the VIMS, which informs the operator of the exhaust temperature.

Some causes of high exhaust temperature may be faulty injectors, plugged air filters, or a restriction in the turbochargers or the muffler.

If the exhaust temperature is above 750° C (1382° F), the Engine ECM will derate the fuel delivery to prevent excessive exhaust temperatures. The ECM will derate the engine by 2% for each 30 second interval that the exhaust temperature is above 750° C (1382° F) (maximum derate of 20%). The ECM will also log an event that requires a factory password to clear.

92


93

This schematic shows the flow through the air induction and exhaust system.

The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers.

The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercoolers. After the air is cooled by the aftercoolers, the air flows to the cylinders and combines with the fuel for combustion.


(..��

��'��

�.��

/+*7)��2��21$-�#2�1�

�1$�%=:�-�#��3�#%(

��'��

94

POWER TRAIN

Power flows from the engine to the rear wheels through the power train. The components of the power train are:

- Torque converter- Transfer gears- Transmission- Differential- Final drives

INSTRUCTOR NOTE: In this section of the presentation, component locations and a brief description of the component functions are provided.


��

� ��

Torque Converter

The first component in the power train is the torque converter. The torque converter provides a fluid coupling that permits the engine to continue running with the truck stopped. In converter drive, the torque converter multiplies engine torque to the transmission. At higher ground speeds, a lockup clutch engages to provide direct drive. The NEUTRAL and REVERSE ranges are converter drive only. FIRST SPEED is converter drive at low ground speed and direct drive at high ground speed. SECOND through SIXTH SPEEDS are direct drive only. The torque converter goes to converter drive between each shift (during clutch engagement) to provide smooth shifts.

Mounted on the torque converter are the inlet relief valve (1), the outlet relief valve (2), and the torque converter lockup clutch control valve (3).

A torque converter outlet temperature sensor (4) provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends the signal to VIMS, which informs the operator of the torque converter outlet temperature.

A Converter Output Speed (COS) sensor (5) sends an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM uses the information to calculate shift times for the torque converter lockup clutch and the transmission clutches. The shift time information is sent to VIMS for shift time analysis.

95


12

34

5

96

This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (yellow piston and blue discs) is not engaged. During operation, the rotating housing and impeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationary and multiplies the torque transfer between the impeller and the turbine. The output shaft rotates slower than the engine crankshaft, but with increased torque.


��

#��@-%��16%�#%��16%�#%��$�26%

��"��

#��A��"�� &�

#�� 2'"��

��'��

#��A��2��

97

In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine to the impeller. The housing, impeller, turbine, and output shaft then rotate as a unit at engine rpm. The stator, which is mounted on a freewheel assembly, is driven by the force of the oil in the housing and will freewheel at approximately the same rpm.


��

#��@-%��16%�#%�$2�%�#�$�26%

��"��

#��A��

��"�� &�

#�� 2'"��

��

��'��

#��A��

2��

Torque Converter Hydraulic System

The three (785C) or four (789C) section torque converter pump is located at the bottom rear of the torque converter. The four sections (from the front to the rear) are:

- Torque converter scavenge (1)- Torque converter charging (2)- Parking brake release (3)- Rear brake oil cooling (4) (789C only)

Excess oil that accumulates in the bottom of the torque converter is scavenged by the first section of the pump through a screen behind the access cover (5) and returned to the hydraulic tank.

98


12

3

4 5

Oil flows from the torque converter charging section of the pump to the torque converter charging filter (1).

An oil filter bypass switch (2) is located on the torque converter charging filter. The oil filter bypass switch provides an input signal to the VIMS, which informs the operator if the filter is restricted.

99


1

2

Oil flows from the torque converter charging filter to the torque converter inlet relief valve (1). The inlet relief valve limits the maximum pressure of the supply oil to the torque converter. The torque converter inlet relief pressure can be measured at this valve by removing a plug and installing a pressure tap. Inlet relief pressure should not exceed 930 ± 35 kPa (135 ± 5 psi) at high idle when the oil is cold. Normally, the inlet relief pressure will be slightly higher than the outlet relief valve pressure.

Oil flows through the inlet relief valve and enters the torque converter.

Some of the oil will leak through the torque converter to the bottom of the housing to be scavenged. Most of the oil in the torque converter is used to provide a fluid coupling and flows through the torque converter outlet relief valve (2). The outlet relief valve maintains the minimum pressure inside the torque converter. The main function of the outlet relief valve is to keep the torque converter full of oil to prevent cavitation. The outlet relief pressure can be measured at the tap (3) on the outlet relief valve. The outlet relief pressure should be:

785C: 345 to 585 kPa (50 to 85 psi) at 1640 ± 65 rpm (TC Stall)

789C: 345 to 585 kPa (50 to 85 psi) at 1715 ± 65 rpm (TC Stall)

A torque converter outlet temperature sensor (4) provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to VIMS, which informs the operator of the torque converter outlet temperature.

100


12 3

4

Most of the oil from the torque converter outlet relief valve flows through the torque converter outlet screen (1) located outside the left frame.

A torque converter outlet screen bypass switch (2) provides an input signal to the VIMS, which informs the operator if the torque converter outlet screen is restricted.

Oil flows from the torque converter outlet screen to the front brake oil cooler located behind the engine.

Oil flows from the parking brake release section of the torque converter pump to the parking brake release filter (3).

A parking brake release filter bypass switch (4) is located on the parking brake release filter. The bypass switch provides an input signal to the Brake ECM. The Brake ECM sends a signal to VIMS, which informs the operator if the parking brake release filter is restricted.

101


1234

The oil from the torque converter outlet screen flows through a diverter valve (1) before flowing through the front brake oil cooler (2). When the retarder or service brakes are ENGAGED, the oil is diverted through the cooler to the brakes. When the brakes are RELEASED, the oil bypasses the cooler and flows directly to the brakes.

Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

102


1

2

Oil from the parking brake release filter flows to the parking brake release valve (1). The parking brake release section of the torque converter pump provides supply oil for several purposes:

- Release the parking brakes- Engage the torque converter lockup clutch- Hoist valve pilot oil- Front (789C) or rear (785C) brake oil cooling

The parking brake relief valve (2) controls the pressure for parking brake release, torque converter lockup and hoist valve pilot oil. The parking brake release pressure is 4700 ± 200 kPa (680 ± 30 psi).

Most of the oil from the parking brake release valve flows to the front brake oil cooler on the 789C truck and to the rear brake oil coolers on the 785C truck.

103


1

2

The parking brake release pump supplies oil to the torque converter lockup clutch valve through the inlet port (1). When the lockup clutch solenoid (located on the transmission housing) is energized by the Transmission/Chassis ECM, transmission pump supply oil (signal oil) enters the lockup valve through the center hose (2). The signal oil pressure is approximately 1725 kPa (250 psi). The signal oil causes the lockup valve to start the modulation process for torque converter lockup. The lockup clutch valve then supplies oil to ENGAGE the lockup clutch in the torque converter.

Torque converter lockup clutch pressure can be measured at the tap (3). Torque converter lockup clutch pressure should be 2135 ± 70 kPa (310 ± 10 psi) at 1300 rpm or higher. Do not check the torque converter lockup clutch pressure below 1300 rpm.

The Converter Output Speed (COS) sensor (4) sends an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM memory also contains the engine rpm and the Transmission Output Speed (TOS) for each gear of the transmission. The Transmission/Chassis ECM provides all of these input signals to the VIMS.

Using the information from the Transmission/Chassis ECM, the VIMS calculates if any slippage exists in the torque converter lockup clutch or any transmission clutches and stores this information in the VIMS main module. This information can be downloaded from the VIMS with a laptop computer.

104


1

2

34

105

Shown is a sectional view of the torque converter lockup clutch valve in DIRECT DRIVE. Supply oil from the parking brake release pump is used to provide lockup clutch oil.

First, supply pressure is reduced to provide pilot pressure to the relay valve. Supply oil to the pressure reduction valve flows through cross-drilled orifices in the spool, past a check valve, and enters the slug chamber. The check valve dampens spool movement and reduces the possibility of valve chatter and pressure fluctuation. Oil pressure moves the slug in the right end of the spool to the right and the spool moves to the left against the spring force. The slug reduces the effective area on which the oil pressure can push. Because of the reduced effective area, a smaller, more sensitive spring can be used. Pilot pressure will be equal to the force of the spring on the left end of the spool. The spring force can be adjusted with shims. Pilot pressure is 1725 ± 70 kPa (250 ± 10 psi).

When the lockup solenoid is energized, transmission pump supply (signal) pressure is directed to the relay valve. Before moving the selector piston, the pilot oil moves a shuttle valve to the right, which closes the lower left drain passage and opens the check valve. Oil then flows to the selector piston. Moving the selector piston blocks the upper drain passage, and the load piston springs are compressed.


��"��

��'�#��' ��&��'"

��6��

��"�� &�

6��

��"�(��

6��

��"��

�6!

#��"�� -!

��'�� &�)��'"� �(�!

#��@-%��16%�#%��,-��-#�:��1#��$2�%�#�$�26%

��6��

��

#��#��' ��

��

#��

B$B

� &��

When the solenoid is energized, supply oil from the parking brake release pump is reduced to provide the lockup clutch pressure. Lockup clutch pressure depends mainly on the force of the load piston valve springs. When the solenoid is energized, pilot oil moves the selector piston down against a stop. When the load piston that compresses the springs is at the top against the selector piston, lockup clutch pressure is at its lowest controlled value. This value is called "primary pressure." As the load piston moves down, lockup clutch pressure increases gradually until the load piston stops. Maximum lockup clutch pressure is then reached. The gradual increase in pressure, which depends on how fast the load piston moves, is called "modulation."

The speed of the load piston movement depends on how fast the oil can flow to the area above the load piston. The load piston orifice meters the flow of oil to the load piston chamber and determines the modulation time.

Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is not adjustable. If the primary pressure is correct and final lockup clutch pressure is incorrect, the load piston should be checked to make sure that it moves freely in the selector piston. If the load piston moves freely, the load piston springs should be replaced.


106

This schematic shows the flow of oil from the torque converter pump through the torque converter hydraulic system on the 789C truck.

The scavenge pump section pulls oil through a screen from the torque converter housing and sends the oil to the hydraulic tank.

The charging pump section sends oil through the torque converter charging filter to the torque converter inlet relief valve. Oil flows from the inlet relief valve through the torque converter to the outlet relief valve. Oil flows from the outlet relief valve through the converter outlet filter and the front brake oil cooler to the front brakes.

The parking brake release pump section sends oil through the parking brake release filter to the parking brake release valve and the torque converter lockup clutch valve. Most of the oil flows through the parking brake release valve and the front brake oil cooler to the front brakes.

The brake cooling pump section of the torque converter pump (789C only) sends oil through the two oil coolers located on the right side of the engine to the rear brakes.


#��@-%��16%�#%��:3$��-�2��3�#%(

��)��

#��A��& �&��

��)��

�� &�)��

��6��

$ ��6��

��

�� &�)��

��)��

��)��

#��:� �� (�� .��

��&��

��

�� .�6��

2�� .�6��

��"�6��

Transmission and Transfer Gears

Power flows from the torque converter through a drive shaft to the transfer gears (1). The transfer gears are splined to the transmission input shaft.

The transmission (2) is located between the transfer gears and the differential (3). The transmission is electronically controlled and hydraulically operated as in all other ICM (Individual Clutch Modulation) transmissions in Caterpillar rigid frame trucks.

The differential is located in the rear axle housing behind the transmission. Power from the transmission flows through the differential and is divided equally to the final drives in the rear wheels. The final drives are double reduction planetaries.

107


1

2

3

Oil flows from the transmission oil cooler to the transfer gears through a hose (1). Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.

The transmission lube pressure relief valve is in the transmission case near the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission lube circuit. Transmission lube oil pressure can be measured at the tap (2).

At HIGH IDLE, the transmission lube pressure should be 140 to 205 kPa (20 to 30 psi). At LOW IDLE, the transmission lube pressure should be a minimum of 4 kPa (.6 psi).

The Transmission Output Speed (TOS) sensor (3) is located on the front of the transfer gears. A small shaft runs from the speed sensor location through the entire length of the transmission and engages the transmission output shaft. The transmission speed sensor signal serves many purposes. Some of the purposes are:

- Transmission automatic shifting- Speedometer operation- Traction Control System (TCS) top speed limit- Truck Production Management System (TPMS) distance calculations- Machine speed input to VIMS to determine some warning categories

108


12

3

109

The transmission is a power shift planetary design which contains six hydraulically engaged clutches. The transmission provides six FORWARD speeds and one REVERSE speed.


* 7 /

8

+ C

��9%��:2�#��1%#��3�#��1�(2��2�1

Transmission Hydraulic System

The transmission pump pulls oil through a suction screen from the transmission tank (see Visuals No. 12 and 159) located on the right side of the truck.

The three-section transmission pump is mounted on the rear of the pump drive, which is located inside the right frame near the torque converter. The three sections are:

- Transmission scavenge (1)- Transmission lube (2)- Transmission charging (3)

The transmission scavenge section pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is sent to the transmission tank.

110


1 2 3

Shown is the location of the transmission magnetic scavenge screens (arrow). These screens should always be checked for debris if a problem with the transmission is suspected.

Oil is scavenged from the transmission by the first section of the transmission pump (see Visual No. 110).

111


Oil flows from the charging section of the transmission pump to the transmission charging filter (1) located on the frame behind the right front tire.

Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. A transmission oil temperature sensor (2) is located in the tube between the transmission charging filter and the transmission control valve. The temperature sensor provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to VIMS, which informs the operator of the transmission oil temperature.

Oil flows from the lube section of the transmission pump to the transmission lube filter (3).

Oil flows from the transmission lube filter through the transmission oil cooler to the transfer gears. Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.

An oil filter bypass switch is located on each filter. The oil filter bypass switches provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator if the filters are restricted.

Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (4).

112


1

2

3

4

Oil flows from the transmission lube filter and the transmission control valve through the transmission oil cooler bypass valve (1) to the transmission oil cooler (2). The bypass valve for the transmission oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is restricted.

Oil flows from the transmission oil cooler to the transfer gears and the transmission to cool and lubricate the internal components.

113


1

2

The transmission charging pump supplies oil to the transmission hydraulic control valve and the shift solenoids through the inlet port (1). Excess transmission charging oil either drops to the bottom of the housing to be scavenged or flows to the transmission oil cooler through the outlet hose (2).

The torque converter lockup clutch solenoid (3) is energized by the Transmission/Chassis ECM when DIRECT DRIVE (lockup clutch ENGAGED) is required. Transmission charge pump supply (signal) oil flows through the small hose (4) to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.

The transmission charging pressure relief valve is part of the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission charging circuit. Transmission charging pressure can be measured at the tap (5).

114


12

3

4

5

Shown is the Individual Clutch Modulation (ICM) transmission hydraulic control valve. Transmission clutch pressures are measured at the pressure taps (1).

The transmission hydraulic control valve contains a priority valve. The priority valve controls the pressure that is directed to the selector pistons in each of the clutch stations. The transmission priority valve pressure is 1720 kPa (250 psi).

The transmission lube pressure relief valve (2) limits the maximum pressure in the transmission lube circuit.

The "D" Station (3) is used to control the dual stage relief valve setting for the clutch supply pressure. In DIRECT DRIVE, the pressure measured at the tap for station "D" will be approximately 1380 kPa (200 psi). This valve station is adjusted to obtain the correct transmission charge pressure in DIRECT DRIVE.

At LOW IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be 2515 kPa (365 psi) minimum. At HIGH IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be 3175 kPa (460 psi) maximum.

During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals. At 1300 rpm in DIRECT DRIVE, the clutch supply pressure should be 2020 + 240 - 100 kPa (293 + 35 - 15 psi). The corresponding transmission charge pressure is reduced to 2100 ± 100 kPa (305 ± 15 psi).

115


1

2 3

4

To test the transmission clutch pressures in torque converter lockup (DIRECT DRIVE), disconnect the signal line (4) and install a plug in the hose and a cap on the fitting. An 8T5200 Signal Generator/Counter can be used to shift the transmission during the diagnostic tests. If a Signal Generator is not available, disconnect the upshift and downshift solenoids and rotate the rotary selector spool manually by inserting a 1/4 in. ratchet extension through the transmission case.


116

Shown is a sectional view of the ICM transmission hydraulic control valve group. The rotary selector spool is in a position that engages two clutches. Pump supply oil from the lockup solenoid flows to the selector piston in station "D." Station "D" reduces the pump supply pressure, and the reduced pressure flows to the lower end of the relief valve. Providing oil pressure to the lower end of the relief valve reduces the clutch supply pressure.


$�� .��

-"� .��

��"��

�

�

:

�

)

�

��"��

1�� D��6��

��

6��

$�� .��

-"� .��

#��' ��

#��' ��#��

��& �&��'"

��'" ��&��

�'"

��)�"��6��

� ��

�� .�6��

�'"��

#��#��A��6��

��6��"�� .�6��

��"�$��&�� .�6��

��

��

��"

� ��

$

%

��

1*

/

� ��

#��1�(2��2�1�2�(�:3$��-�2��3�#%(

117

Shown is the transmission hydraulic system. The transmission pump pulls oil through a suction screen from the transmission tank.

The three-section transmission pump is mounted on the rear of the pump drive, which is located inside the right frame near the torque converter. The three sections are:

- Transmission scavenge- Transmission lube- Transmission charging

The transmission scavenge section pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is sent to the transmission tank.


#��' ��& �&��

� &��#��"�6��

(�&�� &��

#��' ��

#��' ��

#��' ��'"

��

>?+��>?E��#��1�(2��2�1�:3$��-�2��3�#%(

Oil flows from the charging section of the transmission pump to the transmission charging filter. Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. Transmission charging oil flows from the transmission control valve and joins with the oil from the transmission lube section of the transmission pump.

Oil flows from the lube section of the transmission pump to the transmission lube filter.

Oil from the transmission lube filter and the transmission control valve flows through the transmission oil cooler. Oil flows from the transmission oil cooler to the transfer gears and the transmission to cool and lubricate the internal components.


Differential

Shown is the differential removed from the rear axle housing. The rear axle cooling and filter system starts with a rear axle pump (1) that is driven by the differential. Since the pump rotates only when the machine is moving, no oil flow is produced when the machine is stationary. Cooling oil flow increases with ground speed to provide cooling when it is most needed.

The rear axle pump pulls oil from the bottom of the rear axle housing through a suction screen (2). Oil flows from the pump through a temperature and flow control valve located on top of the differential housing to a filter mounted on the rear of the axle housing. Oil then flows from the filter back to the valve located on top of the differential housing. Oil then flows from the valve to the rear wheel bearings and the differential bearings.

Oil flows through tubes (3) to the differential bearings.

The fiberglass shroud (4) reduces the temperature of the rear axle oil on long hauls by reducing the oil being splashed by the bevel gear.

118


1

2

3

4

Oil flows from the pump through the large hose (1) to the rear axle temperature and flow control valve (2). A differential oil temperature sensor (3) and pressure sensor (4) are located on the temperature and flow control valve. The sensors provide input signals to the Brake ECM. The Brake ECM sends signals to the VIMS.

The differential temperature sensor input signal is used to warn the operator of a high rear axle oil temperature condition or to turn on the attachment rear axle cooling fan (if equipped).

The differential oil pressure sensor input signal is used to warn the operator of a HIGH or LOW rear axle oil pressure condition.

A HIGH oil temperature warning is provided if the temperature is above 118° C (244° F).

A LOW oil pressure warning is provided if the pressure is below35 kPa (5 psi) when the differential oil temperature is above 52° C (125° F) and the ground speed is higher than 24 km/h (15 mph).

A HIGH oil pressure warning is provided if the pressure is above 690 kPa (100 psi) when the differential oil temperature is above 52° C (125° F).

119


1

2

3

4

5

The temperature and pressure control valve (2) prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43° C (110° F), the valve is OPEN and allows oil to flow to the rear axle housing. When the oil temperature is above 43° C (110° F), the valve is CLOSED and all the oil flows through the filter to a flow control valve located in the temperature and flow control valve. The temperature and pressure control valve is also the system main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter.

The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings.

Oil flows from the temperature and flow control valve to the differential oil filter mounted on the rear of the axle housing. Oil then flows from the filter back to the temperature and flow control valve. Some of the oil that flows from the temperature and flow control valve flows through the small supply hose (5) to the differential bearings.


The differential oil filter bypass switch (1) and the two rear axle oil level switches (2) (one behind differential filter) provide input signals to the Brake ECM. The Brake ECM sends signals to the VIMS.

The differential oil filter bypass switch signal is used to warn the operator when the differential oil filter is restricted.

The rear axle oil level switch input signals are used to warn the operator when the rear axle oil level is LOW.

When the truck is initially put into operation, a 1R0719 (40 micron) filter is installed. This filter removes the rust inhibitor used during manufacturing. The 40 micron filter should be changed after the first 50 hours of operation and replaced with a 4T3131 (13 micron) filter. The 13 micron filter should be changed every 500 hours.

A differential carrier thrust pin is located behind the small cover (3). The thrust pin prevents movement of the differential carrier during high thrust load conditions.


1

23

120

121

Shown is a schematic of the rear axle oil cooling and filter system. The differential oil pump pulls oil from the bottom of the rear axle housing through a suction screen. Oil flows from the pump through a temperature and flow control valve located on top of the differential housing.

The temperature and pressure control valve, which is part of the temperature and flow control valve, prevents high oil pressure when the rear axle oil is cold. When the oil temperature is below 43° C (110° F), the valve is OPEN and allows oil to flow to the rear axle housing. When the oil temperature is above 43° C (110° F), the valve is CLOSED and all the oil flows through the differential oil filter and the oil cooler (if equipped) to a flow control valve, which is also part of the temperature and flow control valve.

The temperature and pressure control valve is also the system main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature and pressure control valve will open to prevent high oil pressure to the rear axle oil filter.

The flow control valve distributes the oil flow to the rear wheel bearings and the differential bearings. At high ground speeds, excess oil flow is diverted to the axle housing to prevent overfilling the wheel bearing and final drive compartments.


� ��

#�'"��

��6��

�%��=�%��2��21��1$��2�#%��3�#%(

#�'"��6��

$ ..�� '"

��

��5��

122

Final Drives

Shown is a sectional view of the double reduction planetary gear final drive. Power flows from the differential through axles to the sun gear of the first reduction planetary set. The ring gears of the first reduction planetary set and the second reduction planetary set cannot rotate. Since the ring gears cannot rotate, the first reduction sun gear causes rotation of the first reduction planetary gears and the first reduction carrier.

The first reduction carrier is splined to the second reduction sun gear. The second reduction sun gear causes rotation of the second reduction planetary gears and the second reduction carrier. Since the second reduction carrier is connected to the wheel assembly, the wheel assembly also rotates.

The wheel assembly rotates much slower than the axle shaft but with increased torque.


� �� &��

�� &��

��

��

��

� ��

� ��

� ��

�21��$�26%

Transmission/Chassis Electronic Control System

The Transmission/Chassis Electronic Control Module (ECM) (arrow) is located in the compartment at the rear of the cab. The transmission control used in the "B" Series trucks is referred to as the second generation Electronic Programmable Transmission Control (EPTC II).

The transmission control used in the "C" Series trucks performs the transmission control functions, plus some other machine functions (hoist control). Because of the added functionality of the control, it is now referred to as the "Transmission/Chassis ECM."

The Transmission/Chassis ECM does not have a diagnostic window as in the EPTC II. Diagnostic and programming functions must be performed with an Electronic Control Analyzer Programmer (ECAP) or a laptop computer with the Electronic Technician (ET) software installed. ET is the tool of choice because the Transmission/Chassis ECM can be reprogrammed with a "flash" file using the WinFlash application of ET. The ECAP cannot upload "flash" files.

The Transmission/Chassis ECM appears identical to the Engine ECM with two 40-pin connectors, but the Transmission/Chassis ECM does not have fittings for cooling fluid. Also, the Transmission/Chassis ECM has no access plate for a personality module.

123


124

The purpose of the Transmission/Chassis ECM is to determine the desired transmission gear and energize solenoids to shift the transmission up or down as required based on information from both the operator and machine.

The Transmission/Chassis ECM receives information (electrical signals) from various input components such as the shift lever switch, Transmission Output Speed (TOS) sensor, transmission gear switch, body position sensor, and the hoist lever sensor.

Based on the input information, the Transmission/Chassis ECM determines whether the transmission should upshift, downshift, engage the lockup clutch, or limit the transmission gear. These actions are accomplished by sending signals to various output components.

Output components include the upshift, downshift and lockup solenoids, the back-up alarm, and others.

The Transmission/Chassis ECM also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores diagnostic codes for retrieval at the time of service.


:� ��

)��"��'��

��

�� .��

,��

-"� .��

��"��

�

)��

21�-#��(��1%1#� �-#�-#��(��1%1#�

#��' ��

#��' ��"��"��

�� &��)��

�� )��

��

��"��"��

%�& ��"��"��

:� ��

)��%�(

%�& ��%�(

%�� #��

��#�$��

62(�

$�� .��

:� ��

��

�� &��

#��' ��&��

#��' �� #�'"��

:� ��

#��' ��

#��A�� #�'"��

)��-"��'"

B�B��%�2%��#�-�,�#��1�(2��2�1��:��2��%�%�#��12��1#��3�#%(�

The Engine Electronic Control, the Brake Electronic Control System (ARC and TCS), the Vital Information Management System (VIMS) and the Transmission/Chassis Electronic Control System all communicate through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the Transmission/Chassis ECM signals the Engine ECM to reduce or increase engine fuel during a shift to lower stress to the power train.

The Transmission/Chassis ECM is also used to control the hoist, the automatic lubrication (grease), the neutral-start and the back-up alarm systems on the "C" Series trucks.

Many of the sensors and switches that provided input signals to the VIMS interface modules on the "B" Series trucks have been moved to provide input signals to the Transmission/Chassis ECM and the Brake ECM. Sensors and switches that were in the VIMS and now provide input signals to the Transmission/Chassis ECM are:

- Low steering pressure - Hoist screen bypass- Transmission oil temperature - Transmission charge filter bypass- Transmission lube filter bypass - Torque converter oil temperature

The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used to perform several diagnostic and programming functions.

Some of the diagnostic and programming functions that the service tools can perform are:

- Display real time status of input and output parameters- Display the internal clock hour reading- Display the number of occurrences and the hour reading of the first and last occurrence for

each logged diagnostic code and event- Display the definition for each logged diagnostic code and event- Display load counters- Display the lockup clutch engagement counter- Display the transmission gear shift counter- Program the top gear limit and the body up gear limit- Upload new Flash files


The shift lever (also referred to as the "Cane" or "Gear Selector") switch (1) is located inside the cab in the shift console and provides input signals to the Transmission/Chassis ECM. The shift lever switch controls the desired top gear selected by the operator. The shift lever switch inputs consist of six wires. Five of the six wires provide codes to the Transmission/Chassis ECM. Each code is unique for each position of the shift lever switch. Each shift lever switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM. The other three wires remain open (ungrounded). The pair of grounded wires is unique for each shift lever position. The sixth wire is the "Ground Verify" wire, which is normally grounded. The Ground Verify wire is used to verify that the shift lever switch is connected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish between loss of the shift lever switch signals and a condition in which the shift lever switch is between detent positions.

To view the shift lever switch positions or diagnose problems with the switch, use the VIMS message center module or the status screen of the ET service tool and observe the "Gear Lever" status. As the shift lever is moved through the detent positions, the Gear Lever status should display the corresponding lever position shown on the shift console.

The position of the shift lever can be changed to obtain better alignment with the gear position numbers on the shift console by loosening the three nuts (2) and rotating the lever. The position of the shift lever switch is also adjustable with the two screws (3).

125


1

23

The transmission gear switch (1) provides input signals to the Transmission/Chassis ECM. The transmission gear switch inputs (also referred to as the "actual gear inputs") consist of six wires. Five of the six wires provide codes to the Transmission/Chassis ECM. Each code is unique for each position of the transmission gear switch. Each transmission gear switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM. The other three wires remain open (ungrounded). The pair of grounded wires is unique for each gear position.

The sixth wire is the "Ground Verify" wire, which is normally grounded. The Ground Verify wire is used to verify that the transmission gear switch is connected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish between loss of the transmission gear switch signals and a condition in which the transmission gear switch is between gear detent positions. Earlier transmission gear switches use a wiper contact assembly that does not require a power supply to Pin 4 of the switch. Current transmission gear switches are Hall-Effect type switches. A power supply is required to power the switch. A small magnet passes over the Hall cells, which then provide a non-contact position switching capability. The Hall-Effect type switch uses the same 24-Volt power supply used to power the Transmission/Chassis ECM. The solenoid outputs provide +Battery voltage to the upshift solenoid (2), the downshift solenoid (3) or the lockup solenoid (4) based on the input information from the operator and the machine. The solenoids are energized until the transmission actual gear switch signals the Transmission/Chassis ECM that a new gear position has been reached.

126


1

2

3

4

The Transmission Output Speed (TOS) sensor (arrow) is located on the transfer gear housing on the input side of the transmission. Although the sensor is physically located near the input end of the transmission, the sensor is measuring the speed of the transmission output shaft. The sensor is a Hall-Effect type sensor. Therefore, a power supply is required to power the sensor. The sensor receives 10 Volts from the Transmission/Chassis ECM. The sensor output is a square wave signal of approximately 10 Volts amplitude. The frequency in Hz of the square wave is exactly equal to twice the output shaft rpm. The signal from this sensor is used for automatic shifting of the transmission. The signal is also used to drive the speedometer and as an input to other electronic controls.

An 8T5200 Signal Generator/Counter can be used to shift the transmission during diagnostic tests. Disconnect the harness from the lockup solenoid and the speed sensor and attach the Signal Generator to the speed sensor harness. Depress the ON and HI frequency buttons. Start the engine and move the shift lever to the highest gear position. Rotate the frequency dial to increase the ground speed and the transmission will shift.

NOTE: A 196-1900 adapter is required to increase the frequency potential from the signal generator when connecting to the ECM’s used on these trucks. When using the signal generator, the lockup clutch will not engage above SECOND GEAR because the Engine Output Speed (EOS) and the Converter Output Speed (COS) verification speeds will not be correct for the corresponding ground speed signal.

127


The service/retarder brake switch (1) is located in the compartment behind the cab. The switch is normally closed and opens when service/retarder brake air pressure is applied. The switch has three functions for the Transmission/Chassis ECM:

- Signals the Transmission/Chassis ECM to use elevated shift points, which provides increased engine speed during downhill retarding for increased oil flow to the brake cooling circuit.

- Cancels Control Throttle Shifting (CTS).- Signals the Transmission/Chassis ECM to override the anti-hunt timer.

Rapid upshifting and downshifting is always allowed. The anti-hunt timer prevents a rapid upshift-downshift sequence or a rapid downshift-upshift sequence (transmission hunting). The timer is active during normal operation. It is overridden when either the service/retarder or parking/secondary brakes are engaged.

A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within two hours of operation time.

The Traction Control System (TCS) also uses the service/retarder brake switch as an input through the CAT Data Link (see Visual No. 199).

128


1

2

3

4

5

The parking/secondary brake switch (2) is in the parking/secondary brake air pressure line. The normally open switch is closed during the application of air pressure. The purpose of the switch is to signal the Transmission/Chassis ECM when the parking/secondary brakes are ENGAGED. Since the parking/secondary brakes are spring engaged and pressure released, the parking/secondary brake switch is closed when the brakes are RELEASED and opens when the brakes are ENGAGED. This signal is used to override the anti-hunt timer for rapid downshifting and is used to sense when the machine is parked.

A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within one hour of operation time.

Many relays (3) are located behind the cab. Some of these relays receive output signals from the Transmission/Chassis ECM, and the relays turn on the desired function. The back-up alarm relay is one of the Transmission/Chassis ECM output components located behind the cab. When the operator moves the shift lever to REVERSE, the Transmission/Chassis ECM provides a signal to the back-up alarm relay, which turns ON the back-up alarm.

The system air pressure sensor (4) and the brake light switch (5) are also located in the compartment behind the cab. The low air pressure sensor provides an input signal to the Brake ECM. The Brake ECM sends a signal to the VIMS, which informs the operator of the system air pressure condition.


The body position sensor (1) is located on the frame near the left body pivot pin. A rod assembly (2) is connected between the sensor and the body. When the body is raised, the rod rotates the sensor, which changes the Pulse Width Modulated (PWM) signal that is sent to the Transmission/Chassis ECM. The adjustment of the rod between the sensor and the body is very important. The length of the rod must be within 10 mm (.39 in.) of the following dimensions (center to center of the rod ends):

350 ± 3 mm (13.78 ± .12 in.)

After the rod has been adjusted, a calibration should be performed. The body position sensor is calibrated by the Transmission/Chassis ECM when the following conditions occur:

- Engine is running- Hoist output is in FLOAT or LOWER- No ground speed is present for one minute- Body position sensor duty cycle output is stable for 23 seconds (body is down)- Body position is different than previous calibration- Duty cycle output from the sensor is between 3% and 30%

Use the VIMS display to view the body position. When the body is down, the VIMS should display zero degrees. If the position is greater than zero degrees, the sensor rod may have to be adjusted.

129


1

2

The body position signal is used for several purposes.

- Body up gear limiting- Hoist snubbing- Signals a new load count (after 10 seconds in RAISE position)- Lights the body up dash lamp- Allows the VIMS to provide body up warnings

The body position sensor signal is used to limit the top gear into which the transmission will shift when the body is UP. The body up gear limit value is programmable from FIRST to THIRD gear using the ECAP or ET service tool. The Transmission/Chassis ECM comes from the factory with this value set to FIRST gear. When driving away from a dump site, the transmission will not shift past the programmed gear until the body is down. If the transmission is already above the limit gear when the body goes up, no limiting action will take place.

The body position sensor signal is also used to control the SNUB position of the hoist control valve. When the body is being lowered, the Transmission/Chassis ECM signals the hoist LOWER solenoid to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame.

The body position sensor signal is used to provide warnings to the operator when the truck is moving with the body UP. The faster the ground speed, the more serious the warning.

The body position sensor receives + Battery Voltage (24 Volts) from the Chassis ECM. To check the supply voltage to the sensor, connect a multimeter between Pins A and B of the connector. Set the meter to read "DC Volts."

The body position sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the body position. To check the output signal of the body position sensor, disconnect the rod and connect a multimeter between Pins B and C of the connector. Set the meter to read "Duty Cycle." The duty cycle output of the body position sensor should change smoothly between 3% and 98% when rotated. The duty cycle should be low when the body is DOWN and high when the body is UP.


130

STEERING SYSTEM

This section of the presentation explains the operation of the steering system. As on other Caterpillar Off-highway Trucks, the steering system uses hydraulic force to change the direction of the front wheels. The system has no mechanical connection between the steering wheel and the steering cylinders.

If the oil flow is interrupted while the truck is moving, the system incorporates a secondary steering system. Secondary steering is accomplished by accumulators which supply oil flow to maintain steering.

The steering system on the "C" Series trucks is the same as the steering system on the "B" Series trucks. No changes were made to the steering system.


��

��

131

When the engine is started, oil for the steering system is drawn from the steering hydraulic tank by the steering pump and sent through a one-way check valve to the solenoid and relief valve manifold. Oil from the solenoid and relief valve manifold flows to the steering directional valve, the accumulator charging valve and the accumulators. After the oil pressure increases to a predetermined pressure in both accumulators, the steering pump will destroke.

When a steering demand occurs, the accumulators supply the necessary oil flow for steering, and pressure in the accumulators decreases. When the oil pressure in the accumulators decreases to a predetermined level, the steering pump will automatically upstroke to maintain the oil pressure required for steering in the accumulators.

Oil from the accumulators flows through the steering directional valve to the Hand Metering Unit (HMU).

If the steering wheel is not turned, the oil flows through the HMU and the main steering oil filter to the tank.


� ��

��

��

! "��#��$$��"��%�

��%��#��$$��"��%

�!

#

�

!�

#�$� ��#�&'

(��&�� %��

��)��*��+��(,�� -!*.

��$��-��

Allowing oil to circulate through the HMU while the steering wheel is stationary provides a "thermal bleed" condition, which maintains a temperature differential of less than 28°C (50°F) between the HMU and the tank. This "thermal bleed" prevents thermal seizure of the HMU (sticking steering wheel).

When the steering wheel is turned, the HMU directs oil back to the steering directional valve. The steering directional valve directs oil to the steering cylinders. Depending on which direction the steering wheel is turned, oil will flow to the head end of one steering cylinder and to the rod end of the other cylinder. The action of the oil on the pistons and rods in the steering cylinders causes the wheels to change direction. Displaced oil from the steering cylinders flows through the back pressure valve in the steering directional valve and returns through the main steering oil filter to the tank.


132

Oil from the steering pump flows through a one-way check valve to the solenoid and relief valve return manifold and is then sent to the accumulators and the Hand Metering Unit (HMU). The 785C truck does not use a steering directional valve. Oil from the HMU flows through a crossover relief valve group directly to the steering cylinders.

In the HOLD position, oil flows through an orifice in the HMU to the tank. Allowing oil to flow through the HMU in the HOLD position provides a "thermal bleed" condition, which prevents thermal seizure of the HMU (sticking steering wheel).

The crossover relief valves protect the steering cylinders and oil lines from pressure surges when the steering wheel is in the HOLD position by equalizing the oil pressure between the head ends and rod ends of the steering cylinders.

During a turn, the HMU directs oil through the crossover relief valves to the steering cylinders. Displaced oil from the steering cylinders flows back through the HMU to the main steering oil filter.


�� $$ ��$

��

#�$� ��#�&'

#�&'�

�"��%

� ��

��

��$��

-��

/��)��*!�

The steering tank is located on the right platform. Two sight gauges are on the side of the tank. When the engine is shut off and the oil is cold, the oil should be visible between the FULL and ADD OIL markings of the upper sight gauge (l). When the engine is running and the accumulators are fully charged, the oil level should not be below the ENGINE RUNNING marking of the lower sight gauge (2). If the ENGINE RUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity.

A combination vacuum breaker/pressure relief valve is used to limit the tank pressure. Before removing the fill cap, be sure that the engine was shut off with the key start switch and the oil has returned to the tank from the accumulators. Depress the pressure release button (3) on the breather to vent any remaining pressure from the tank.

Supply oil for the steering system is provided by a piston-type pump. Case drain oil from the pump returns to the tank through the filter (4). The remaining steering system oil returns to the tank through the main steering filter (5). Both filters are equipped with bypass valves to protect the system if the filters are restricted or during cold oil start-up.

If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at the connector to charge the steering accumulators. Steering capability is then available to tow the truck.

133


1

2

3

4

5

6

7

The steering oil temperature sensor (7) provides an input signal to the VIMS, which informs the operator of the steering system oil temperature. If the steering oil temperature exceeds 108 °C (226 °F), the operator will receive a warning on the VIMS display (STRG OIL TEMP HI).

INSTRUCTOR NOTE: For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).


The piston-type steering pump (1) for the 785C truck is mounted to the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter.

The steering pump operates only when the engine is running and provides the necessary oil flow to the accumulators for steering system operation.

The steering pump for the 785C truck contains a pressure compensator valve (2) that monitors and controls steering pump output.

134


12

135

Shown is a sectional view of the piston-type steering pump for the 785C truck in the MAXIMUM FLOW condition. No oil pressure is present in the control piston. In this condition, the swashplate is kept at maximum angle by the force of the spring in the pump housing. The pistons travel in and out of the barrel and maximum flow is provided through the outlet port. Since the pump is driven by a shaft off the engine, it should be remembered that engine rpm also affects pump output.


�"�$%'�� #�$� �

��''�0�*��

*��'��*��

#��$$�� &'��$��

� �� #�$� ��'��

/��# �#��(,�� -!*.

136

Shown is a sectional view of the pump compensator valve for the 785C truck. The pump compensator valve senses pump supply pressure through a passage in the valve body. When the outlet pressure is less than the force of the spring on the end of the compensator spool, the oil is blocked from flowing to the pump control piston.

As the accumulators fill, the pressure of the oil through the pump outlet increases. The pump supply pressure will increase until the pressure of the oil in the pump passage in the pump compensator valve is high enough to overcome the spring force on the compensator spool. The spool then moves to the left and opens the passage to the control piston. This movement occurs when the outlet oil pressure is approximately 17580 ± 345 kPa (2550 ± 50 psi).

The pressure setting can be adjusted by changing the shim thickness behind the compensator spool spring. Remove the plug and add shims to increase the pressure setting. Remove shims to lower the setting.


� �

� �� #�$� �

��#�$$��$

# �#��*�#��(�*��(!��

�(,�� # �#�-!*.

� �

� �� #�$� �

��#�$$��$

�� # �#�-!*.

-� &�#�&'

-� &�#�&'

137

The pressure of the oil from the compensator valve passage moves the control piston, which rotates the swashplate toward the minimum angle. The pistons now have very little movement in and out of the barrel as the retraction plate and slippers follow the minimum angle of the swashplate.

While the accumulators are filled, this small movement of the pistons maintains the pressure at the setting of the pressure compensator valve. The compensator spool will remain open to provide pressure oil behind the control piston. Excess oil from the pump outlet goes into the pump case for cooling and lubrication. The oil then goes through a drain line to the case drain oil filter and steering hydraulic tank.

As the steering wheel is turned and oil is taken from the accumulators, the pressure at the pump outlet will decrease. When accumulator pressure decreases, the pressure compensator valve will allow the swashplate to move toward maximum angle and increase pump output.


�"�$%'�� #�$� �

��''�0�#�$$�� #�&'

*��'��#�$$��-� &�#�&'

#��$$�� &'��$��

� �� #�$� �

/��# �#�� -!*.

The 789C is equipped with a load sensing, pressure compensated, piston-type pump (1). The steering pump is mounted to the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter.

The steering pump operates only when the engine is running and provides the necessary flow of oil to the accumulators for steering system operation. The steering pump contains a load sensing controller (2) that works with an accumulator charging valve to monitor and control steering pump output.

The steering pump will produce flow at high pressure until the steering accumulators are charged with oil and the pressure increases to 18300 ± 350 kPa (2655 ± 50 psi) at LOW IDLE. This pressure is referred to as the CUT-OUT pressure. When the CUT-OUT pressure is reached, the accumulator charging valve reduces the load sensing signal pressure to the pump load sensing controller, and the pump destrokes to the LOW PRESSURE STANDBY condition. During LOW PRESSURE STANDBY, the pressure should be between 2070 and 3600 kPa (300 and 525 psi).

The pump operates at minimum swashplate angle to supply oil for lubrication and leakage. Because of the normal leakage in the steering system and Hand Metering Unit (HMU) "thermal bleed," the pressure in the accumulators will gradually decrease to 16470 ± 350 kPa (2390 ± 50 psi). This pressure is referred to as the CUT-IN pressure.

138


1

2

34

When the pressure in the accumulators decreases to the CUT-IN pressure, the accumulator charging valve blocks the load sensing signal line to the load sensing controller from returning to the tank, and the pump upstrokes to maximum displacement (full flow).

A pressure tap (3) is located on the pump pressure switch manifold. If steering pump supply pressure is measured at this tap during LOW PRESSURE STANDBY, a gauge acceptable for testing maximum steering system pressure must be used to avoid damaging the gauge when the steering pump upstrokes to provide maximum oil flow.

Two pressure switches monitor the condition of the steering system on the 789C. One switch (4) monitors the output of the steering pump. This switch monitors pump supply pressure during LOW PRESSURE STANDBY. The VIMS refers to this switch as the "low steering pressure" switch.

The other steering pressure switch is mounted on the bottom of one of the steering accumulators (see Visual No. 153). This switch monitors the steering system accumulator pressure. The VIMS refers to this switch as the "high steering pressure" switch.

Both steering pressure switches provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator of the condition of the steering system. A steering system warning is only displayed if the ground speed is above 8 km/h (5 mph) or the actual gear switch is not in NEUTRAL.


On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold (2). The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve (3), the accumulators and the steering directional valve (4). The solenoid and relief valve manifold also provides a path to drain for the steering oil.

When checking the steering system CUT-OUT and CUT-IN pressures, a gauge can be connected at the pressure tap (5).

Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (6).

139


1

2

3

4

56

140

After the engine is started, pressure increases in the steering accumulators. The pump load sensing controller is spring biased to vent the actuator piston pressure to drain. Venting pressure from the load sensing controller and the actuator piston positions the spring biased swashplate to maximum displacement (full flow).

As pressure increases in the accumulators, pump supply pressure is sensed in the accumulator charging valve and on both ends of the flow compensator. With pressure on both ends of the flow compensator, the swashplate is kept at maximum angle by the force of the spring in the pump housing and pump discharge pressure on the swashplate piston. The pistons travel in and out of the barrel and maximum flow is provided through the outlet port. Since the pump is driven by the engine, engine rpm also affects pump output.

NOTE: Because the signal lines are sensing pump supply pressure and not a "load" pressure, the steering system does not operate the same as other load sensing systems with a margin pressure.


#�&'�*��'��

! ��$��

#��$$��

(��&��

�%��

� �(��&�� $�

-� &�(��&�� $�

! ��$��

� ��

-� "�

� &'��$��

�"�$%'��

#�$� �

(��

#�$� �

�(,�� -!*.

��# �#

141

Pump supply pressure will increase until the accumulator pressure acting on the accumulator charging valve shifts the spool, and the load sensing signal pressure is vented to the tank. The accumulator charging valve spool shifts (cut-out) when the pump outlet oil pressure is approximately 18300 ± 350 kPa (2655 ± 50 psi).

An orifice prevents supply pressure from filling the drained load sensing passage above the flow compensator. Pump oil (at low pressure standby pressure) flows past the lower end of the displaced flow compensator spool to the actuator piston. The actuator piston has a larger surface area than the swashplate piston. The oil pressure at the actuator piston overcomes the spring force of the swashplate piston and moves the swashplate to destroke the pump. The pump is then at a low flow, LOW PRESSURE STANDBY condition. Pump output pressure is equal to the setting of the flow compensator. The LOW PRESSURE STANDBY setting must be between 2070 and 3600 kPa (300 and 525 psi).

In the NEUTRAL or NO STEER position, demand for oil from the accumulators is low. The pump operates at minimum swashplate angle to supply oil for lubrication and leakage. Because of the normal leakage in the steering system and HMU "thermal bleed," the pressure in the accumulators will gradually decrease to approximately 16470 ± 350 kPa (2390 ± 50 psi) (90% of the accumulator charging valve cut-out pressure).


#�&'�*��'��

! ��$��

#��$$��

!*.�#�� (��1)

� �(��&�� $�

-� &�(��&�� $�

! ��$��

� ��

��# �#

-� "�� &'��$��

(��&�� %��

�"�$%'��#�$� �

(�� #�$� �

When the pressure in the accumulators decreases to 16470 ± 350 kPa (2390 ± 50 psi), the accumulator charging valve shifts (cut-in) and blocks the load sensing signal line pressure from the tank. Pump supply oil flows through the orifice and pressurizes the load sensing signal line. The load sensing signal shifts the flow compensator spool and drains the actuator piston oil to the tank. Venting pressure from the actuator piston positions the spring biased swashplate to maximum displacement (full flow).

At LOW lDLE in the NEUTRAL or NO STEER position, the pump will cycle between the cut-out and cut-in conditions in 25 seconds or more. Connecting a pressure gauge to the pressure tap on the bottom of the steering directional valve will indicate these steering system pressures. If pump pressure cycles in less than 25 seconds, leakage is in the system and must be corrected. Typical sources of leakage can be the accumulator bleed down solenoid or the back-up relief valve located on the return manifold.


Shown is the accumulator charging valve (1). The accumulator charging valve is located on the frame rail near the front of the truck and below the engine oil pan.

The pressure setting of the accumulator charging valve can be changed by adjusting the spring force that keeps the valve seated (closed). Change the setting by removing the protective cap (2) and turning the adjustment screw clockwise to increase or counterclockwise to decrease the pressure setting. Do not exceed 14 N•m (10 lb. ft.) torque on the adjustment screw when making the adjustments. One turn of the adjustment screw changes the pressure approximately 4000 kPa (580 psi).

Operate the engine at LOW IDLE and check the pump (accumulator) pressure at the pressure tap (3). The pump will cycle between cut-out and cut-in every 25 seconds or more. The pressure gauge will indicate these steering system pressures. Turn the adjusting screw until the cut-out pressure is correct.

If the accumulator charging pressure cannot be adjusted within specifications, an adjustment of the high pressure cutoff valve is required. The high pressure cutoff setting must be a minimum of 1720 kPa (250 psi) higher than the accumulator charging valve setting.

NOTE: When testing or adjusting any steering system pressure settings, always allow the accumulator charge cycle to occur at least three times before testing the pressures. Failure to allow the charging cycle to occur three times will result in inaccurate readings.

142


1 2

3

143

Pump pressure limiting (high pressure cutoff) is adjustable. To adjust the pump high pressure cutoff valve, turn the accumulator charging valve adjustment screw all the way in, or disconnect the load sensing (LS) line (pump to accumulator charging valve) at the pump. Plug the line to the accumulator charging valve and cap the fitting on the pump. Operate the engine at LOW IDLE, and check the pump (accumulator) pressure at the pressure tap below the steering directional valve.

Turn the compensator (high pressure cutoff) adjusting screw while watching the pressure gauge. One turn is equal to approximately 2800 kPa (405 psi). Adjust the pressure to 20000 ± 350 kPa (2900 ± 50 psi). When the adjustment is complete, reconnect the LS line to the pump.

The high pressure cutoff setting must be a minimum of 1720 kPa (250 psi) higher than the accumulator charging valve setting. If the high pressure cutoff setting of the compensator valve (in the load sensing controller) is lower than the accumulator charging valve setting, the pump will stay at MINIMUM FLOW, and the steering system will take too long to recharge. The high pressure cutoff adjustment provides a back-up if the accumulator charging valve malfunctions.


��%�#��$$��

(�2�$�&��"

� ��3

� �(�� #�$� �

-� &�#�&'�*��'��# ��

! "�#��$$��

��40�(�2�$�&��"

(��&�� %��

-� &�(��&��

��$� ��#��!��

� ��

��%�#��$$�� $�

� �

(��&��

!*(��*��*!!��

Pump LOW PRESSURE STANDBY is also adjustable. Connect a gauge to the low pressure standby pressure tap (see Visual No. 138). With the signal line connected, operate the engine at LOW IDLE and check the pump pressure. The pump will cycle to low pressure standby every 25 seconds or more. Low pressure standby must be between 2070 and 3600 kPa (300 and 525 psi). If adjustment is required, stop the engine.

Turn the low pressure standby adjustment screw clockwise to increase the pressure and counterclockwise to decrease the pressure until the pressure is between 2070 and 3600 kPa (300 and 525 psi). Each 1/4 turn changes the pressure setting approximately 345 kPa (50 psi).

NOTE: If the steering pump is adjusted on a hydraulic test stand, set the margin pressure to 2070 ± 100 kPa (300 ± 15 psi) with a flow of 115 ± 12 L/min (30 ± 3 gpm), 1838 rpm and 15000 kPa (2180 psi) discharge pressure. The low pressure standby reading measured on a truck is higher than the test stand margin pressure due to parasitic loads in the truck steering system.


On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold. The solenoid and relief valve manifold connects the steering pump to the accumulator charging valve, the accumulators and the steering directional valve. The solenoid and relief valve manifold also provides a path to drain for the steering oil.

The check valve (1) prevents accumulator oil from flowing back to the steering pump when the pump destrokes to LOW PRESSURE STANDBY.

The accumulator bleed down solenoid (2) drains pressure oil from the accumulators when the truck is not in operation.

The back-up relief valve (3) protects the system from pressure spikes if the pump cannot destroke fast enough or limits the maximum pressure if the steering pump high pressure cutoff valve does not open.

Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (4).

To operate the steering system on a disabled truck, an Auxiliary Power Unit (APU) can be connected to the secondary steering connector (5) on the solenoid and relief valve manifold and to a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil to charge the accumulators. Steering capability is then available to tow the truck.

144


1

2 3 4

5

On the 785C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold. The solenoid and relief valve manifold connects the steering pump to the accumulators and the HMU. The solenoid and relief valve manifold also provides a path to drain for the steering oil.

The check valve (1) prevents accumulator oil from flowing back to the steering pump

The accumulator bleed down solenoid (not shown) drains pressure oil from the accumulators when the truck is not in operation.

The back-up relief valve (2) limits the maximum pressure if the steering pump compensator valve fails.

Steering system oil samples can be taken at the steering system Scheduled Oil Sampling (S•O•S) tap (3)

To operate the steering system on a disabled truck, an Auxiliary Power Unit (APU) can be connected to the secondary steering connector (4) on the solenoid and relief valve manifold and to a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil to charge the accumulators. Steering capability is then available to tow the truck.

The 785C has two accumulators (5). The steering system pressure tap (6) is located on the bottom of the left steering accumulator.

145


1

23

4

5

6

146

Shown is a sectional view of the solenoid and relief valve manifold. The accumulator bleed down solenoid is energized by the bleed down solenoid shutdown control (see Visual No. 154) when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds.

Pressure oil from the accumulators is sensed by the bleed down solenoid. When the solenoid is ENERGIZED, the plunger moves and connects the pressure oil to the drain passage. Pressure oil flows through an orifice, past the plunger, to the tank. The orifice limits the return oil flow from the accumulators to a rate which is lower than the flow limit (restriction) of the steering oil filter in the hydraulic tank. When the solenoid is DE-ENERGIZED, spring force moves the plunger and pressure oil cannot go to drain.


�

1��35�'��

��

1�� "��

�*!��*��(��

��!��-��(!��(��-*!�

� �+�-� &�

(��&�� $

��''�0�

-� &�#�&'

� ��3

� ��

� ��

The back-up relief valve protects the steering system if the steering pump malfunctions (fails to destroke). Pressure oil from the steering pump works against the end of the back-up relief valve and the spring. The relief valve unseats (opens) if the pressure reaches approximately:

785C: 20700 ± 400 kPa (3000 ± 60 psi) at 8 ± 2 L/min (2 ± .5 gpm)

789C: 20670 ± 400 kPa (3000 ± 60 psi) at 8 ± 2 L/min (2 ± .5 gpm)

Oil then flows past the relief valve and drains to the tank.

The back-up relief valve must be adjusted only on a test bench. The pressure setting of the back-up relief valve can be changed by adjusting the spring force that keeps the relief valve seated (closed). To change the relief valve setting, remove the protective cap and turn the adjustment screw clockwise to increase or counterclockwise to decrease the pressure setting. One revolution of the setscrew will change the pressure setting 3800 kPa (550 psi).

A functional test of the back-up relief valve can be performed on the machine by installing a manual hydraulic pump at the location of the Auxiliary Power Unit (APU) connector and installing blocker plates to prevent oil from flowing to the accumulators. See the service manual for more detailed information.

NOTE: Using the functional test procedure to adjust the back-up relief valve will provide only an approximate setting. Accurate setting of the back-up relief valve can only be performed on a hydraulic test bench.


The steering directional valve (1) used on the 789C truck is pilot operated from the HMU in the operator’s station. Five pilot lines connect these two components. The pilot lines send pilot oil from the HMU to shift the spools in the steering directional valve. The spools control the amount and direction of pressure oil sent to the steering cylinders. Four pilot lines are used for pump supply, tank return, left turn, and right turn. The fifth pilot line is for the load sensing signal.

When checking the steering system cut-out and cut-in pressures, a gauge can be connected at the pressure tap (2).

147


1

2

148

Shown is a sectional view of the steering directional valve. The main components of the steering directional valve are: the priority spool, the amplifier spool with internal combiner/check spool, the directional spool, the relief/makeup valves and the back pressure valve.

Pressure oil from the accumulators flows past the spring biased priority spool and is blocked by the amplifier spool. The same pressure oil flows through an orifice to the right end of the priority spool. The orifice stabilizes the flow to the priority spool and must be present to open and close the priority spool as the flow demand changes. The same pressure oil flows to the HMU. After all the passages fill with pressure oil, the priority spool shifts to the left, but remains partially open. In this position, the priority spool allows a small amount of oil flow (thermal bleed) to the HMU and decreases the pressure to the HMU supply port. The "thermal bleed" prevents the HMU from sticking.

With the truck in the NEUTRAL or NO TURN position, all four working ports (supply, tank, right turn, and left turn) are vented to the tank through the HMU. The directional spool is held in the center position by the centering springs.


��+��3��'��

!��0��

1��3�#��$$��

!��#�� *��

(&'��' ��

��%��#�� *��

�� &4��+��%��3�

�' �

! ��$��# ��

-� &�(��&��

#�� 0��' �

��*�(!��(!��

��%��0��

��+��3��'��

�� ''�0��%��&��1��

�*��

� ��3

While the truck is traveling straight (no steer), any rolling resistance (opposition) acting on the steering cylinders creates a pressure increase. The increased pressure acts on the relief/makeup valve in that port. If the pressure increase exceeds 28000 ± 1000 kPa (4065 ± 150 psi), the relief poppet will open. A pressure drop occurs across the orifice. The pressure drop causes the dump valve to move and allows oil to flow to the tank passage.

The relief action causes the makeup portion of the other relief/makeup valve to open and replenish oil to the low pressure ends of the cylinders.

The excess (dumped) oil flows across the back pressure valve and enters the outer end of the other relief/makeup valve. A pressure difference of 48 kPa (7 psi) between the tank passage and the low pressure cylinder port causes the makeup valve to open. The excess oil flows into the low pressure cylinder port to prevent cavitation of the cylinder. The back pressure valve also prevents cavitation of the cylinders by providing a positive pressure of 170 kPa (25 psi) in the passage behind the makeup valve. A pressure higher than 170 kPa (25 psi) will open the back pressure valve to the tank.

The steering directional valve must be removed and tested on a hydraulic test bench to accurately check the setting of the relief/makeup valves.

A functional test of the relief/makeup valves can be performed on the machine by connecting a manual hydraulic pump and installing blocker plates to prevent oil from flowing to the steering cylinders. See the service manual for more detailed information.

NOTE: Using the functional test procedure to adjust the relief/makeup valves will provide only an approximate setting. Accurate setting of the relief/makeup valves can only be performed on a hydraulic test bench.


149

When the steering wheel is turned to the RIGHT, the "thermal bleed" and venting of the four work ports to the tank is stopped. The increased supply pressure flows to the HMU and the load sensing pilot line. The load sensing pilot line directs cylinder pressure to the priority spool in the directional valve. Cylinder pressure is present in the HMU because pilot oil combines with accumulator oil in the combiner/check valve spool in the directional valve. The increased pressure in the load sensing line causes the priority spool to move to the right and allows more oil flow to the HMU through the supply line. The load sensing port supply pressure varies with the steering load. The priority spool moves proportionally, allowing sufficient oil flow to meet the steering requirements.

Pilot oil flows through a stabilizing orifice to the right turn pilot port of the directional valve and moves the directional spool. Movement of the directional spool allows pilot oil to flow to the amplifier and combiner/check spools.

The pilot oil divides at the amplifier spool. Pilot oil flows through a narrow groove around the combiner/check spool. The pilot oil is momentarily blocked until the amplifier spool moves far enough to the right to allow partial oil flow through one of eight orifices.


(&'��' ��

1��3�#��$$��

!��#�� *��

��%��#�� *��

�� &4��+��%��3�

�' �

! ��$��# ��

-� &�(��&��

�� ''�0��%��&��1��

#�� 0��'

��*�(!��(!��

��

��+��3��'��

!��0��

��%��0��

��+&�3��'��

� ��3

Pilot oil also flows through a connecting pin hole and a stabilizing orifice to the left end of the amplifier spool and causes the amplifier spool to move to the right. Accumulator oil at the spring end (right end) of the amplifier spool flows through a mid-connecting pin to the left end of the amplifier spool and also causes the amplifier spool to move to the right.

When the amplifier spool moves to the right, accumulator oil flows to the inner chamber, forcing the combiner/check spool to the left. Accumulator oil then flows through seven of the eight orifices. Pilot and accumulator oil combine. Oil flows across the directional spool (which has already shifted) for a RIGHT TURN.

The faster the steering wheel is turned, the farther the directional spool and the amplifier spool are shifted. A higher flow rate is available, which causes the truck to turn faster. The ratio of pilot and pump supply oil that combine is always the same because one orifice is dedicated to pilot flow and seven orifices are dedicated to accumulator supply flow.

Return oil from the cylinders flows across the directional spool, around the relief/makeup valve, forces the back pressure valve open and returns to the tank.

During a turn, if a front wheel strikes a large obstruction that cannot move, oil pressure in that steering cylinder and oil line increases. Oil flow to the cylinder is reversed. This pressure spike is felt in the amplifier spool. The combiner/check spool moves to the right and blocks the seven pump supply oil orifices to the steering cylinders. The amplifier spool moves to the left and blocks the pilot oil orifice. Pilot oil flow to the steering cylinders stops. The pressure spike is not felt at the HMU. If the pressure spike is large enough, the relief/makeup valve drains the pressure oil to the tank as previously described.


Shown is the solenoid and relief valve manifold (1) and the crossover relief valves (2) on the 785C truck.

The crossover relief valves (2) are located in one housing mounted on the inside of the left frame rail near the front of the truck. The crossover relief valves prevent damage from high pressure oil in the steering cylinder circuit caused by an outside force applied to a front wheel when the steering wheel is stationary.

The crossover relief valve housing contains two pressure taps (3) where steering system pressure can be measured. One tap shows pressure during a left turn and the other tap shows pressure during a right turn.

To check the steering system pressure, turn the steering wheel completely in either direction. Operate the engine at LOW IDLE. Continue to turn the steering wheel after the wheels have stopped and the pressure will increase to the pump compensator valve setting. Check the steering pressure while turning in both directions. The pump compensator valve setting should be observed on the gauge in both directions. If the pressure readings are different, one of the crossover relief valve settings is probably incorrect. A misadjusted valve must be removed and readjusted on a test bench.

On the 785C, one pressure switch (4) monitors the condition of the steering system. The switch provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to the VIMS.

150


1

2

3

4

151

On the 785C truck, when the steering wheel is stationary, the HMU blocks oil in the steering cylinders and in the lines between the steering cylinders and the HMU. The oil blockage prevents the front wheels from moving when the steering wheel is not turned. If pressure is applied against the front wheels while the steering wheel is stationary, the pressure of the oil increases in the head end of one cylinder and the rod end of the other cylinder. If the increase of oil pressure exceeds 18270 kPa (2650 psi) at the affected crossover relief valve, the valve will open. Oil from the high pressure ends of the steering cylinders then transfers to the low pressure ends of the cylinders.


�� $$ ��

��$

��

��

/��*��*��!��-��)��,��(!��#(��

The 789C Hand Metering Unit (HMU) (arrow) is located at the base of the steering column behind a cover at the front of the cab. The HMU is connected to the steering wheel and controlled by the operator.

The 789C HMU meters the amount of oil sent to the steering directional valve by the speed at which the steering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steering cylinders from the steering directional valve, and the faster the wheels will change direction.

The 785C HMU is larger because oil flows directly from the HMU, through the crossover relief valve, to the steering cylinders. The capacity of the 785C HMU must be large enough to handle the flow required to fill the steering cylinders and allow satisfactory steering cycle times.

On the front of the HMU are four ports:

- Return to tank - Left turn

- Pump supply - Right turn

The 789C HMU has a fifth port on the side of the HMU. The fifth port is the load sensing signal line to the steering directional valve.

152


Two steering accumulators (1) provide the supply oil during normal operation and temporary secondary steering if a loss of pump flow occurs (789C shown).

Inside each accumulator is a rubber bladder that is charged with nitrogen. The nitrogen charge provides energy for normal steering and secondary steering capability if steering pump flow stops.

To check the secondary steering system, the engine must be shut off with the manual engine shutdown switch (see Visual No. 25) while leaving the key start switch in the ON position. When the manual shutdown switch is used, the bleed down solenoid is not energized and the accumulators do not bleed down. The truck can then be steered with the engine stopped.

The steering accumulator pressure switch (2) monitors the steering accumulator pressure. The switch provides an input to the VIMS. The VIMS refers to this switch as the "high steering pressure" switch.

High pressure oil remains in the accumulators if the manual shutdown switch is used. To release the oil pressure in the accumulators, turn the key start switch to the OFF position and turn the steering wheel left and right until the oil is drained from the accumulators (steering wheel can no longer be turned).

153


1

2

Shown is the shutdown control (arrow) for the steering accumulator bleed down solenoid. The control is located in the compartment behind the cab.

The steering accumulator bleed down solenoid is activated by the control when the key start switch is moved to the OFF position. The bleed down solenoid shutdown control holds the solenoid open for 70 seconds.

The charge pressure for the steering accumulators is:

785C: 8270 ± 0 kPa (1200 ± 0 psi)789C: 5512 ± 345 kPa (800 ± 50 psi)

154


155

HOIST SYSTEM

The hoist system on the 785C and 789C trucks is electronically controlled by the Transmission/Chassis ECM. The hoist control system operates similarly to the earlier trucks. The four operating positions are: RAISE, HOLD, FLOAT, and LOWER.

The hoist valve has a fifth position referred to as the SNUB position. The operator is unaware of the SNUB position because a corresponding lever position is not provided. When the body is being lowered, just before the body contacts the frame, the Transmission/Chassis ECM signals the hoist solenoids to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame.

The hoist system can be enabled or disabled using ET. All trucks shipped from the factory without bodies installed are set at the Hoist Enable Status 2. The Hoist Enable Status 2 is a test mode only and will prevent the hoist cylinders from accidentally being activated. After the body is installed, change the Hoist Enable Status to 1 for the hoist system to function properly.


�*��)��

��

The operator controls the hoist lever (arrow). The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER.

The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist control valve will actually be in the SNUB position.

If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until:

1. The hoist lever is moved into the HOLD or FLOAT position; and2. the shift lever has been cycled into and out of NEUTRAL.

NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, the lever must be moved into HOLD and then FLOAT before the body will lower.

156


The hoist lever controls a Pulse Width Modulated (PWM) position sensor (arrow). The PWM sensor sends duty cycle input signals to the Transmission/Chassis ECM. Depending on the position of the sensor and the corresponding duty cycle, one of the two solenoids located on the hoist valve is energized.

The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER, but since the sensor provides a duty cycle signal that changes for all positions of the hoist lever, the operator can modulate the speed of the hoist cylinders.

The hoist lever sensor also replaces the body raise switch (transmission neutralizer switch) that was located behind the operator's seat. The hoist lever sensor performs three functions:

- Raises and lowers the body- Neutralizes the transmission in REVERSE- Starts a new TPMS cycle

The hoist lever position sensor receives 24 Volts from the Transmission/ Chassis ECM. To check the supply voltage of the sensor, connect a multimeter between Pins A and B of the sensor connector. Set the meter to read "DC Volts."

To check the output signal of the hoist lever position sensor, connect a multimeter between Pins B and C of the hoist lever position sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the sensor should be approximately 5 to 95% between full RAISE to full LOWER.

157


Shown is the hoist, converter and brake oil hydraulic tank (1) and the oil level sight gauges (2). The oil level is normally checked with the upper sight gauge. The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running.

The lower sight gauge is used when filling the hydraulic tank with the hoist cylinders in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge as explained above.

Use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 or newer.

TDTO-4 oil:

- Provides maximum frictional capability required for clutch discs used in the brakes.- Increases brake holding capability by reducing brake slippage.- Controls brake chatter.

Check the hydraulic tank breather (3) for restriction. Clean the filter if it is restricted.

158


1

2

3

Shown is the rear of the transmission and hoist hydraulic tank and the converter and brake oil hydraulic tank. The hoist system pumps pull oil from the hydraulic tank through the suction screens (arrows) located in the rear of the tank.

159


The hoist system oil for the "C" Series Trucks is supplied by a two-section pump (1) located at the top rear of the pump drive. Oil flows from the hoist pump through two screens to the hoist valve. The hoist system pressure can be tested at the two pressure taps (2).

The hoist system relief pressures are different in the RAISE and LOWER positions.

The hoist system relief pressure during RAISE is:

785C/789C: 17225 + 700 - 0 kPa (2500 + 100 - 0 psi)789C (with cast iron pump): 18960 ± 345 (2750 ± 50 psi)

The hoist system relief pressure during LOWER is:

785C/789C: 3450 + 350 - 0 kPa (500 + 50 - 0 psi)

When the body is in the DOWN position, the hoist valve will be in the SNUB position. The body position sensor rod must be disconnected from the body and the sensor must be rotated to the RAISE position before the LOWER relief pressure can be tested.

In the HOLD, FLOAT, and SNUB positions, the gauge will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes, and hoses (normally much lower than the actual oil cooler relief valve setting). The maximum pressure is limited by the oil cooler relief valve, which has a setting of 790 ± 20 kPa (115 ± 3 psi).

160


1

22

Oil flows from the hoist pump through the hoist screens (1) to the hoist control valve. Two hoist screen bypass switches (2) provide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator if the hoist screens are restricted.

161


1 2

Oil flows from the hoist pump through two ports (1) (only one visible in this view) to the hoist control valve located inside the right frame next to the hoist cylinder. Two load check valves, one for each pump port, are located below the two plugs (2). The load check valves remain closed until the pump supply pressure is higher than the pressure in the hoist cylinders. The load check valves prevent the body from dropping before the RAISE pressure increases.

The hoist system relief pressures are different in the RAISE and LOWER positions. The RAISE relief valve (3) controls the pressure in the hoist system during RAISE. The LOWER relief valve (4) controls the pressure in the hoist system during LOWER. The relief valve housing must be removed to install shims (see Visual No. 164).

Oil flows through the drain port (5) to the hydraulic tank. When the hoist valve is in the HOLD, FLOAT, or SNUB position, all the hoist pump oil flows through two ports (6), one on each side of the hoist valve, to the two rear brake oil coolers located on the right side of the engine.

162


1

2 34

5

6

A counterbalance valve (1) is mounted on the left side of the hoist valve. The counterbalance valve prevents cavitation of the cylinders when the body raises faster than the pumps can supply oil to the cylinders (caused by a sudden shift of the load). The counterbalance valve signal pressure can be checked at the test port (2) by removing the plug and installing a pressure tap. The counterbalance signal pressure is equal to the RAISE pressure.

An oil cooler relief valve is located behind the large plug (3). The oil cooler relief valve limits the rear brake oil cooling pressure when the hoist valve is in the HOLD, FLOAT, or SNUB position. The setting of the oil cooler relief valve is 790 kPa (115 psi).

The hoist valve uses parking brake release pressure as the pilot oil to shift the directional spool inside the hoist valve. The parking brake release pressure is 4700 ± 200 kPa (680 ± 30 psi).

Pilot pressure is always present at both ends of the directional spool. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool, which then allows the spool to move. On the left is the RAISE solenoid valve (4), and on the right is the LOWER solenoid valve (5).

The RAISE and LOWER solenoid valves are always receiving approximately 300 millivolts at a frequency of 80 Hz when they are in any position except HOLD. The excitation, referred to as "dither," is used to keep the solenoids in a ready state for quick response.

163


1 2 3

4

5

6

7

When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, the Transmission/Chassis ECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. The amount of current sent to the solenoid determines the amount of pilot oil that is drained from the end of the directional spool and, therefore, the distance that the directional spool travels toward the solenoid.

Oil flows through two upper ports (6), one on each side of the hoist valve, to RAISE the hoist cylinders. Oil flows through two lower ports (7), one on each side of the hoist valve, to LOWER the hoist cylinders.


164

Shown is a sectional view of the hoist valve in the HOLD position. Pilot oil pressure is directed to both ends of the directional spool. The spool is held in the centered position by the centering springs and the pilot oil. Passages in the directional spool vent the dual stage relief valve signal stem to the tank. All the hoist pump oil flows through the rear brake oil coolers to the rear brakes.

The position of the directional spool blocks the oil in the head end of the hoist cylinders. Oil in the rod end of the hoist cylinders is connected to the rear brake cooling oil by a small vent slot cut in the directional spool.

A gauge connected to the hoist system pressure taps while the hoist valve is in the HOLD position will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes, and hoses (normally much lower than the actual oil cooler relief valve setting). The maximum pressure in the circuit should correspond to the setting of the rear brake oil cooler relief valve. The setting of the oil cooler relief valve is 790 kPa (115 psi).


� �� $��0��

� �� $��0��

� ��1��3��*�� $

��1��3��

*��

��

#��3��1��3��

��$��#��$$��

! "��

� ��

��$��

� ��

#��3��1��3��

��$��#��$$��

#�&'��''�0�# ��

� ��3

! "�#��$$��

��

��%�#��$$��

��

� ��4��

6�6��*��*��*!��(!��

�*!�

��&

� ��

! ��%��3�

��

��&'��' �

165

Shown is a sectional view of the hoist valve in the RAISE position. The RAISE solenoid is energized and drains pilot oil pressure from the lower end of the directional spool. The directional spool moves down. Pump oil flows past the directional spool to the head end of the hoist cylinders.

When the directional spool is initially shifted, the two load check valves (one shown) remain closed until the pump supply pressure is higher than the pressure in the hoist cylinders. The load check valves prevent the body from dropping before the RAISE pressure increases.

The directional spool also sends hoist cylinder raise pressure to the dual stage relief valve signal stem and the counterbalance valve. The dual stage relief valve signal stem moves down and blocks the supply pressure from opening the low pressure relief valve.


-� &�� $��0��

� �� $��0��

� ��1��3��

*�� $

��1��3��

*��

�� 3

! "�#��$$��

��

��%�#��$$��

��

� ��4��

�(��

� ��

! ��%��3�

��

#��3��1��3��

��$��#��$$��

! "��

� ��

6�6��*��*��*!��(!��

��$��

� ��

#��3��1��3��

��$��#��$$��

#�&'��''�0�# ��

��&

��&'��' �

*�

The counterbalance valve is held open by the hoist cylinder raise pressure. Oil from the rod end of the hoist cylinders flows freely to the rear brake oil coolers. If the body raises faster than the pump can supply oil to the hoist cylinders (caused by a sudden shift of the load) and the raise pressure drops below 2275 kPa (330 psi), the counterbalance valve starts to close and restricts the flow of oil from the rod end of the hoist cylinders. Restricting the flow of oil from the rod end of the hoist cylinders will slow down the cylinders and prevent cavitation. Cavitation in the hoist cylinders can cause the body to drop suddenly when the hoist lever is moved from the RAISE position to the LOWER position.

The pressure in the head end of the hoist cylinders cannot exceed:

785C/789C: 17225 + 700 - 0 kPa (2500 + 100 - 0 psi)789C (with cast iron pump): 18960 ± 345 (2750 ± 50 psi)

The high pressure relief valve will open if the pressure increases above this specification. When the high pressure relief valve opens, the dump spool moves to the left, and pump oil is directed to the rear brake oil coolers.

The high pressure hoist relief valve setting is checked at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the RAISE position and the engine at HIGH IDLE.


166

During RAISE, the counterbalance valve prevents the dump body from running ahead of the hoist pumps if the load shifts rapidly to the rear of the body and attempts to pull the hoist cylinders. Signal pressure from the head end of the hoist cylinders holds the counterbalance valve open. Oil from the rod end of the hoist cylinders flows unrestricted through the counterbalance valve to the tank. If the head end pressure decreases below 2270 kPa (330 psi), the counterbalance valve moves down and restricts the flow of oil from the rod end of the cylinders to the tank.

If no head end signal pressure is present, rod end pressure can still open the counterbalance valve. If the rod end pressure exceeds 6900 ± 690 kPa (1000 ± 100 psi) at the rod end pressure piston, the valve will move up and allow rod end oil to flow from the cylinders to the tank.

During LOWER and FLOAT, the counterbalance valve allows unrestricted flow from the pump through a check valve to the rod end of the hoist cylinders.


�(��

��

��#��$$��

-� &�

� �$��0��

� ��

� ��3

!*.��(��-!*(�

� �

� �$��0��

� ��

-� &�

#�&'

�%��3��

�*��

�* ��1(!(��

�(!��

� ��

#��$$��

#�$� �

167

Shown is a sectional view of the hoist valve in the LOWER (power down) position. The LOWER solenoid is energized and drains pilot oil pressure from the upper end of the directional spool. The directional spool moves up.

Supply oil from the pump flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The supply oil in the rod end of the cylinders and the weight of the body move the cylinders to their retracted positions.

Just before the body contacts the frame, the body position sensor sends a signal to the Transmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUB position, the valve spool moves slightly to restrict the flow of oil and lower the body gently.

The directional spool also vents the passage to the dual stage relief valve signal stem. The dual stage relief valve signal stem allows supply pressure to be limited by the low pressure relief valve.


� �� $��0��

-� &�� $��0��

� ��1��3��*�� $

��1��3��

*��

�� 3

! "�#��$$��

��

��%�#��$$��

��

� ��4��

� ��

! ��%��3�

��

! "��

� ��

��$��

� ��

!*.��7#*.��*.�8

6�6��*��*��*!��(!��

#��3��1��3��

��$��#��$$��

#��3��1��3��

��$��#��$$��

#�&'��''�0�# ��

��&

��&'��' �

*�

If the pressure in the rod end of the hoist cylinders exceeds 3450 + 350 - 0 kPa (500 + 50 - 0 psi), the low pressure relief valve will open. When the low pressure relief valve opens, the dump spool moves to the left and pump oil flows to the rear brake oil coolers.

The low pressure hoist relief valve setting is checked at the two pressure taps located on the hoist pump. Check the relief pressures with the hoist lever in the LOWER position and the engine at HIGH IDLE.

When the body is in the DOWN position, the hoist valve will be in the SNUB position. The body position sensor rod must be disconnected from the body, and the sensor must be rotated to the RAISE position before the LOWER relief pressure can be tested.


168

Shown is a sectional view of the hoist valve in the FLOAT position. The LOWER solenoid is partially energized and drains part of the pilot oil pressure above the directional spool to the tank. The directional spool moves up. Because the pilot pressure is only partially drained, the directional spool does not move as far up as during LOWER.

Pump supply oil flows past the directional spool, through the counterbalance valve, to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The directional valve is in a position that permits the pressure of the oil flowing to the rear brake oil coolers to be felt at the rod end of the hoist cylinders.

The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not the hoist cylinders. The hoist valve will actually be in the SNUB position.

Just before the body contacts the frame, the body position sensor sends a signal to the Transmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUB position, the valve spool moves slightly to restrict the flow of oil and lower the body gently.


� ��1��3��*�� $

��1��3��

*��

�� 3

! "�#��$$��

��

��%�#��$$��

��

� ��4��

-!*(�

� ��

! ��%��3�

��

! "��

� ��

��$��

� ��

6�6��*��*��*!��(!��

#��3��1��3��

��$��#��$$��

#��3��1��3��

��$��#��$$��

#�&'��''�0�# ��

��&

��&'��' �

*�

� �� $��0��

-� &�� $��0��

Shown are the twin two-stage hoist cylinders used to raise and lower the body.

Check the condition of the body pads (arrow) for wear or damage.

To LOWER the body with a dead engine, hoist pilot pressure is required. The towing pump can be used to provide the hoist pilot oil. To lower the body with a dead engine:

- Turn ON the key start switch so the towing motor and the hoist solenoids can be energized.- Move the hoist lever to the RAISE position for 15 seconds, then to the FLOAT position.- Depress the brake retraction switch on the dash (see Visual No. 48).

To RAISE the body with a dead engine, connect an Auxiliary Power Unit (APU) to the hoist cylinders. Follow the same procedure used to lower the body with a dead engine, except keep the hoist lever in RAISE after the 15 seconds interval.

NOTE: For more information on using the APU, refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525 Attachment Group" (Form SEHS8880).

169


170

The hoist system pumps pull oil from the hydraulic tank through suction screens.

Oil flows from the hoist pump through the hoist screens to the hoist control valve.

The hoist valve uses parking brake release pressure as pilot oil to shift the directional spool inside the hoist valve. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool. The solenoid valve on the left is energized in the RAISE position. The solenoid valve on the right is energized in the LOWER or FLOAT position.

When the hoist valve is in the HOLD or FLOAT position, all the hoist pump oil flows through the rear brake oil coolers to the rear brakes.

An oil cooler relief valve is located in the hoist valve. The relief valve limits the rear brake oil cooling pressure when the hoist valve is in the HOLD or FLOAT position.

Two hydraulic cylinders are used to raise the body away from the frame of the truck. When the hoist lever is held in the RAISE position, supply oil flows to the head end of the hoist cylinders and moves the two stage cylinders to their extended lengths. The oil from the rod end of the cylinders flows through the hoist valve to the rear brake oil cooling circuit.


� �� $��0��

� �� $��0��

-� &�#��3��1��3��$��

� �$��#�&' � �$��$

�� $

�*��)��*!�

��1��3��*�� $

��1��3�$

When the hoist lever is moved to the LOWER or FLOAT position and the cylinders are extended, supply oil enters the rod end of the hoist cylinders and lowers the second stage of the cylinders. The oil from the head end of the cylinders flows through the hoist valve to the hydraulic tank.


171

AIR SYSTEM AND BRAKES

Two separate brake systems are used on the "C" Series trucks. The two brake systems are: the parking/secondary brake system and the service/retarder brake system.

The parking/secondary brakes are spring engaged and hydraulically released. The service/retarder brakes are engaged hydraulically by an air-over-oil brake system.

The "C" Series trucks are also equipped with an air system. An engine driven air compressor supplies the air and fills two tanks. Air from the tanks provides energy to perform several functions:

- Engine start-up- Service and retarder brake control- Secondary and parking brake control- Automatic lubrication injection (grease)- Horn, air seat, and cab clean-out


(��)��(��1�(9��

��

Shown is a cutaway illustration of an oil cooled brake assembly. The brakes are environmentally sealed and adjustment free. Oil continually flows through the brake discs for cooling. Duo-Cone seals prevent the cooling oil from leaking to the ground or transferring into the axle housing. The wheel bearing adjustment must be maintained to keep the Duo-Cone seals from leaking.

The smaller piston (yellow) is used to ENGAGE the secondary and parking brakes. The parking brakes are spring ENGAGED and hydraulically RELEASED.

The larger piston (purple) is used to ENGAGE the retarder/service brakes. The retarder/service brakes are engaged hydraulically by an air-over-oil brake system.

172


Air Charging System

The air system is charged by an air compressor mounted on the left front of the engine.

System pressure is controlled by the governor (arrow). The governor maintains the system pressure between 660 and 830 kPa (95 and 120 psi).

The governor setting can be adjusted with a screw below the cover on top of the governor. Turn the adjustment screw OUT to increase the pressure and IN to decrease the pressure.

The capacity of the air charging system has been increased. The air compressor has been increased from a two-cylinder compressor to a four-cylinder compressor. To handle the increased air flow, two larger air dryers are used, and the hoses and tubing have also been increased in size.

To test the air compressor efficiency, lower the air system pressure to 480 kPa (70 psi). Start the engine and raise the engine speed to HIGH IDLE. When the air system pressure reaches 585 kPa (85 psi), measure the time that it takes to build system pressure from 585 kPa (85 psi) to 690 kPa (100 psi). The time to raise the pressure should be 50 seconds or less. If the time recorded is greater than 50 seconds, check for leaks or a restriction in the system. If no leaks or restrictions are found, the air compressor may have a problem.

173


On the 789C truck, air flows from the air compressor to two air dryers (1) located behind the left front tire. The 785C has two air dryers located in front of the left front suspension cylinder.

The air system can be charged from a remote air supply through a ground level connector (2) inside the left frame.

The air dryers remove contaminants and moisture from the air system. The condition of the desiccant in the air dryers should be checked every 250 hours and changed periodically (determined by the humidity of the local climate).

When the air compressor governor senses that system air pressure is at the cut-out pressure of 830 kPa (120 psi), the governor sends an air pressure signal to the purge valve in the bottom of the dryers. The purge valve opens and air pressure that is trapped in the air dryers is exhausted through the desiccant, an oil filter and the purge valve.

An air system relief valve is located on the air dryers to protect the system if the air compressor governor malfunctions.

A heating element in the bottom of the dryers prevents moisture in the dryers from freezing in cold weather.

174


1

2

Air flows through the air dryers and fills two tanks. The service/retarder brake tank (1) is located on the right platform. This tank also supplies air for the air start system.

The second tank is located behind the cab and supplies air for the parking/secondary brake system.

Condensation should be drained from the tank daily through the drain valve (2).

A relief valve located near the tank drain is installed in the service/retarder brake tank. This relief valve protects the air system when the air dryers have exhausted and the ball check valves in the air dryer outlet ports close. The check valves separate the air system from the air dryer relief valves.

175


1

2

Located behind the operator’s station is a pressure protection valve (1). Supply air flows from the large service/retarder brake tank, through the pressure protection valve, to the secondary air system and accessories. The pressure protection valve opens at 550 kPa (80 psi) and closes at 482 kPa (70 psi). If the secondary air lines or an accessory circuit fails, the pressure protection valve maintains a minimum of 482 kPa (70 psi) in the service/retarder brake circuit.

To test the pressure protection valve, drain the air pressure to approximately 345 kPa (50 psi). Use the VIMS display to observe the brake air pressure. With the engine running at LOW IDLE, press the horn button. Record the air pressure when the horn sounds. This pressure reading is the open setting of the pressure protection valve. Slowly drain the air pressure and record the air pressure when the horn turns off. This pressure reading is the setting of the pressure protection valve when it closes.

The air system pressure sensor (2) provides an input signal to the Brake ECM. The Brake ECM sends a signal to the VIMS, which informs the operator if a problem exists in the air system.

Also located behind the operator’s station are the service/retarder brake switch, the parking/secondary brake switch and the brake light switch (see Visual No. 128).

176


2

1

The solenoid air valve (arrow) provides a controlled air supply for the automatic lubrication (grease) system. The solenoid air valve is controlled by the VIMS. The VIMS ENERGIZES the solenoid ten minutes after the machine is started. The VIMS keeps the solenoid ENERGIZED for 75 seconds and then DE-ENERGIZES it. Every 60 minutes thereafter, the VIMS ENERGIZES the solenoid for 75 seconds until the machine is stopped (turned off). These settings are adjustable through the VIMS keypad in the cab.

177


Located behind the operator’s station is the parking/secondary brake air tank. A drain valve is located on the right side of the cab. Moisture should be drained from the tank daily through the drain valve (see Visual No. 33).

A check valve (arrow) prevents a loss of air if an air line breaks upstream of the air tank.

178


179

This schematic shows the flow of air through the 789C air charging system. Air flows from the air compressor, through the two air dryers, to the service/retarder brake tank.

The 785C air charging system is the same as the 789C, but has only one air dryer.

Air from the service/retarder brake tank enters the pressure protection valve. When the pressure in the service/retarder tank reaches 550 kPa (80 psi), the pressure protection valve allows air to flow to the parking/secondary brake tank, the air start system, the automatic lubrication system, and the accessory circuits (horn, air seat, and cab clean-out).

All tanks have a check valve at the air supply port to prevent a loss of air if a leak upstream of the tank occurs.


(�� &'��$$ ��

��

(��

��0��$

#��$$��

#� ��

��

��+��

1��3��3

#��3��+�� 0�

1��3��3

! "�(��

��$ �� (�� !�4��

� �� +��+��5 ��

� �(��

� ��

��(��(��)��

��& ��

��''�0

Brake Systems

The manual retarder valve (arrow) is controlled by the retarder lever in the cab. Normally, the retarder valve blocks air flow to the service brake relay valve near the brake master cylinders and to the front brake oil cooler diverter valve.

When the retarder lever is pulled down, air flows to the service brake relay valve and the front brake oil cooler diverter valve [maximum pressure is approximately 550 kPa (80 psi)]. The retarder lever is used to modulate the service brake engagement by metering the amount of air flow to the service brake relay valve.

The retarder engages the same brakes as the service brake pedal (see Visual No. 43), but is easier to control for brake modulation.

The retarder system allows the machine to maintain a constant speed on long downgrades. The retarder will not apply all of the normal braking capacity.

NOTICEDo not use the retarder control as a parking brake or to stop the machine.

180


The service brake valve (1) is controlled by the brake pedal in the cab. Supply air for the service brake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve (2) is supplied from the manifold (3).

When the service brakes are engaged, air flows from the service brake valve to the service brake relay valve near the brake master cylinders and to the front brake oil cooler diverter valve [maximum pressure is 825 kPa (120 psi)].

The service brake valve engages the same brakes as the retarder, but does not control brake modulation as precisely as the retarder.

Air from the service brake valve and the manual retarder valve flows through the double check valve (4) to the service brake relay valve and through the double check valve (5) to the front brake oil cooler diverter valve. If the manual retarder and the service brakes are engaged at the same time, air from the system with the highest pressure will flow through the double check valves to the service brake relay valve and to the front brake oil cooler diverter valve.

Air from the manual retarder valve also flows through the double check valve (6) to the retarder switch (7). The retarder switch turns on the amber retarder lamp on the dash in the operator’s station when the manual retarder is ENGAGED (see Visual No. 47).

181


1

2

3

4

5

678

The function of the Automatic Retarder Control (ARC) system is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed.

When the ARC is engaged, air flows from the ARC valve to a separate ARC relay valve located near the brake master cylinders. Air also flows from the ARC valve through the double check valve (6), to the retarder switch (7), and through double check valve (5) to the front brake oil cooler diverter valve.

The brake light switch and the service/retarder brake switch (see Visual No. 128) are located in the supply line to the front brake oil cooler diverter valve (see Visual No. 102). The service brake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve send air to these switches when engaged.

The secondary brake valve (8) is controlled by the red pedal in the cab (see Visual No. 43). When the secondary brakes are engaged, air flows from the secondary brake valve to the signal port of an inverter valve (see next visual). The inverter valve then blocks the flow of air from the secondary brake tank to the brake release valve (see Visual No. 183).

Blocking the air from the brake release valve positions the spool in the brake release valve to drain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGE the brakes. The secondary brake valve can be used to modulate parking brake engagement by metering the amount of air flow to the brake release valve.

The parking brake air valve (see Visual No. 44) on the shift console in the cab also controls the flow of air to the brake release valve, but the parking brake air valve does not modulate the parking brake application.

The parking/secondary brake switch (see Visual No. 128) is located in the supply line to the brake release valve. The secondary brake valve and the parking brake air valve send air to this switch when engaged.

INSTRUCTOR NOTE: The ARC system will be discussed in more detail later in this presentation.


When the secondary brakes are engaged, air flows from the secondary brake valve to the signal port (1) of the inverter valve (2). The inverter valve then blocks the flow of air from the secondary brake tank to the brake release valve.

Blocking the air from the brake release valve positions the spool in the brake release valve to drain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGE the brakes.

182


1

2

Oil from the parking brake release pump (see Visual No. 98) flows through the parking brake release filter (see Visual No. 101) to the brake release valve (1) located inside the left frame near the torque converter. Oil flows from the parking brake release valve to the parking brake piston in the brakes when the parking brakes are released.

Supply air from the parking brake air valve in the cab or the secondary brake valve flows through the small hose (2) to an air chamber in the brake release valve. The brake release valve contains an air piston that moves a spool. The spool either directs oil to RELEASE the parking brakes or drains oil to ENGAGE the parking brakes. A relief valve (3) in the brake release valve limits the system pressure for releasing the brakes. The setting of the relief valve is 4700 ± 200 kPa (680 ± 30 psi).

Supply oil flows from the brake release valve through an orifice and a screen (4) to the brake oil makeup tank.

To release the parking brakes for service work or towing, the electric motor that turns the towing pump (5) can be energized by the brake release switch located in the cab (see Visual No. 48). The pump sends oil to the brake release valve to RELEASE the parking brakes. Towing pump pressure is controlled by a relief valve in the towing pump.

183


12

34

5

184

Normally, supply oil flows from the parking brake release pump, through the parking brake release filter, to the parking brake release valve. If air pressure is present from the parking brake air valve or the secondary brake valve, supply oil flows past the relief valve, the check valve, and the spool to RELEASE the parking brakes. The relief valve limits the system pressure for releasing the brakes, torque converter lockup, and for the pilot oil to shift the hoist valve. The setting of the relief valve in the parking brake valve is 4700 ± 200 kPa (680 ± 30 psi).

This schematic shows the flow of oil through the parking brake release system when the towing system is activated.

Oil flow from the parking brake release pump has stopped. The towing motor is energized, and air pressure is present above the parking brake release valve piston. The air pressure moves the spool in the parking brake release valve down to block the drain port.

Oil flows from the towing pump to the parking brake release valve and the parking brakes. The check valve to the right of the parking brake release filter blocks the oil from the towing pump from flowing to the parking brake release pump.


#��3��1��3��

��$��

� "��#�&'�

��

#��3��

1��3��

��$��

#�&'

� "��#�&'�

��

�%��3�

��

� �� $��

#��

�0$��&

��

��

� �

��! �3�'�

��#��3��

1��3��

��$��

-��

-� &��4�� 0�

��#��3��1��3��

�*.��)��

During towing, the parking brake release pressure is limited by a relief valve in the towing pump. When the relief valve opens, oil transfers from the pressure side to the suction side of the towing pump. The setting of the relief valve is approximately 4480 kPa (650 psi).

A check valve in the outlet port of the towing pump prevents oil from flowing to the towing pump during normal operation.

To check the brake release system used for towing, connect a gauge to the parking brake release pressure tap on the rear axle (see Visual No. 189). Use a long gauge hose so the gauge can be held in the cab. With the parking brake air valve in the RELEASE position and the key start switch in the ON position, energize the parking brake release switch used for towing (on the dash). The parking brake release pressure should increase to 4480 kPa (650 psi). Turn off the switch when the pressure stops increasing.

The parking brake release pressure must increase to a minimum of 3790 kPa (550 psi). The parking brakes start to release between 3100 and 3445 kPa (450 and 500 psi). During towing, the brake release switch on the dash must be energized whenever the parking brake release pressure decreases below this level or the brakes will drag. The parking brakes are fully released between 3445 and 3860 kPa (500 and 560 psi).

NOTE: A minimum of 550 kPa (80 psi) air pressure must be available at the parking brake release valve to ensure full release of the brakes for towing.

NOTICEActivate the brake release switch only when additional pressure is required to release the brakes. Leaving the brake release (towing) motor energized continuously will drain the batteries.

The parking brake release pressure setting must not exceed 5445 kPa (790 psi). Exceeding this pressure can cause internal damage to the brake assembly.


185

Shown is the parking/secondary brake hydraulic and air system with the secondary brakes RELEASED and the parking brakes ENGAGED.

Supply air from the parking/secondary brake air tank flows to the secondary brake valve and is blocked from flowing to the inverter valve signal port. Supply air is allowed to flow through the inverter valve and is blocked by the parking brake air valve.

No air pressure is present to move the spool in the parking brake release valve. Supply oil from the parking brake release pump is blocked by the spool. Oil from the parking brake is open to drain through the parking brake release valve, which allows the springs in the parking brake to ENGAGE the brakes.

A parking/secondary brake switch is located in the air line between the parking brake valve and the parking brake release valve. The switch provides an input signal to the Transmission/Chassis ECM. When the parking or secondary brakes are ENGAGED, the switch signals the Transmission/Chassis ECM to allow rapid downshifts.


#��3��1��3��

�� 0�1��3��

#��3��1��3��$��

#(�9��+��*��(�)�1�(9��

#(�9��1�(9��(��

� ��! �3�'�� $��#�� 0$��&

#��3��1��3��$��#�&'

��*��(�)�1�(9��!�(��

#��3��+�� 0�1��3��3

#��3��+�� 0�1��3��"��%

��

The front service brake relay valve (1) receives metered air from only the service brake valve or the manual retarder valve. The rear Automatic Retarder Control (ARC) brake relay valve (2) receives metered air from only the ARC valve.

When the service brakes or manual retarder brakes are ENGAGED, the front relay valve opens and metered air flows from the service brake tank, through the double check valves (3), to the three brake cylinders (4). The brake relay valves reduce the time required to engage and release the brakes. The double check valves (3) are used to separate the service and manual retarder brakes from the ARC brake system.

When the ARC brake system is ENGAGED, the rear relay valve opens and metered air flows from the service brake tank, through a pressure protection valve (5) and the double check valves (3), to the three brake cylinders (4). The pressure protection valve prevents a total loss of air pressure in the service brake air system if the ARC relay valve fails. The protection valve opens to send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below 310 kPa (45 psi).

The brake cylinders operate by air-over-oil. When the metered air enters the brake cylinders, a piston moves down and pressurizes the oil in the bottom of the cylinders. One brake cylinder supplies oil to the front brakes through the slack adjuster (6). Two brake cylinders supply oil to the rear brakes through a separate slack adjuster.

186


12

3 3

45

6

As the brake discs in the brake assemblies wear, more oil is needed from the brake cylinders to compensate for the wear. The brake makeup oil tank (1) supplies makeup oil for the brake cylinders. Oil from the parking brake release valve flows through an orifice and the screen (2) to provide a continuous supply of oil to the makeup tank. Low flow to the makeup tank can cause the makeup oil reserve to decrease and cause the brake cylinders to overstroke.

To check for makeup oil flow, remove the cover from the makeup oil tank. With the engine at HIGH IDLE, a stream of oil filling the tank should be visible. If a stream of oil is not visible, the filter or hose to the tank may be restricted or pump flow may be low.

Keep the service brake ENGAGED for at least one minute. If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke and cause an indicator rod to extend and open the brake overstroke switch (3). The switch provides an input signal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs the operator of the condition of the service/retarder brake oil circuit. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning.

Front brake oil pressure can be measured at the pressure tap (4) located on the front brake slack adjuster.

187


1

23

4

5

The oil-to-air ratio of the brake cylinder is approximately 6.6 to 1. To test the brake cylinder, install a gauge in the fitting on top of the brake cylinder and a gauge on the pressure tap on the slack adjuster. When the service brakes are ENGAGED, if the air pressure in the brake cylinder is 690 kPa (100 psi), the oil pressure measured at the slack adjuster should be approximately 4560 kPa (660 psi). When the brakes are RELEASED, both pressures should return to zero.

Inspect the condition of the breather (5) for the brake cylinders. Oil should not leak from the breathers. Oil leaking from the breathers is an indication that the oil piston seals in the brake cylinder need replacement. Air flow from the breathers during a brake application is an indication that the brake cylinder air piston seals need replacement.


188

This visual shows a sectional view of the brake cylinder when the brakes are ENGAGED.

Air pressure from the brake relay valve enters the air inlet. The air pressure moves the air piston and the attached rod closes the valve in the oil piston. When the valve in the oil piston is closed, the oil piston pressurizes the oil in the cylinder. The pressure oil flows to the slack adjuster.

If air is in the system or a loss of oil downstream from the cylinders occurs, the piston in the cylinder will overstroke, which causes the indicator rod to extend and open the brake overstroke switch. If an overstroke condition occurs, the problem must be repaired and the indicator rod pushed in to end the warning.

When the air pressure is removed from behind the air piston, the spring moves the air piston and the attached rod opens the valve in the oil piston. Any makeup oil that is needed flows into the passage at the top of the oil chamber, through the valve, and into the oil chamber at the right of the oil piston.


(��#�$� �

� ��'��

��

(��

1�(9��)!��1�(9��(��

��

*��#�$� �

-� &��3��'��3

� ��3�(�2�$��

1��%��# ��

The truck is equipped with two slack adjusters--one for the front brakes and one for the rear brakes. The slack adjuster (1) shown is for the rear brakes. The slack adjusters compensate for brake disc wear by allowing a small volume of oil to flow through the slack adjuster and remain between the slack adjuster and the brake piston under low pressure. The slack adjusters maintain a slight pressure on the brake piston at all times.

Brake cooling oil pressure maintains a small clearance between the brake discs.

The service brake oil pressure can be measured at the two taps (2) located on top of the slack adjusters.

Air can be removed from the service brakes through two remote bleed valves (not shown) mounted on the rear axle housing.

The parking brake release pressure can be measured at the two taps (3) on the axle housing.

NOTE: Air can be removed from the front service brakes through bleed valves located on each wheel.

189


1

2 33

190

This visual shows sectional views of the slack adjuster when the brakes are RELEASED and ENGAGED.

When the brakes are ENGAGED, oil from the brake cylinders enters the slack adjusters and the two large pistons move outward. Each large piston supplies oil to one wheel brake. The large pistons pressurize the oil to the service brake pistons and ENGAGE the brakes.

Normally, the service brakes are FULLY ENGAGED before the large pistons in the slack adjusters reach the end of their stroke. As the brake discs wear, the service brake piston will travel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther, the large piston in the slack adjuster moves farther out and contacts the end cover. The pressure in the slack adjuster increases until the small piston moves and allows makeup oil from the brake cylinders to flow to the service brake piston.

When the brakes are RELEASED, the springs in the service brakes push the service brake pistons away from the brake discs. The oil from the service brake pistons pushes the large pistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used to ENGAGE the brakes is replenished at the brake cylinders from the makeup tank.


*��-� "�

� �1��3��

�0��

*��-� "�

-� &�1��3��

�0��

-� &�

.%��

1��3�$

� �

.%��

1��3�$

� �

.%��

1��3�$

1�(9��(��1�(9��!�(��

!��#�$� ��&��#�$� �

-� &�

.%��

1��3�$

�1�(9��!(�9�(�: ��

SERV1857 - 230 - Text Reference06/08SERV1857 - 230 - Text Reference06/08

The spring behind the large piston causes some oil pressure to be felt on the service brake piston when the brakes are RELEASED. Keeping some pressure on the brake piston provides rapid brake engagement with a minimum amount of brake cylinder piston travel.

The slack adjusters can be checked for correct operation by opening the service brake bleed screw with the brakes RELEASED. A small amount of oil should flow from the bleed screw when the screw is opened. The small flow of oil verifies that the spring behind the large piston in the slack adjuster is maintaining some pressure on the service brake piston.

Another check to verify correct slack adjuster operation is to connect a gauge to the pressure tap on top of the slack adjuster and another gauge at the service brake bleed screw location. With system air pressure at maximum and the service brake pedal depressed, the pressure reading on both gauges should be approximately the same.

When the brakes are RELEASED, the pressure at the slack adjuster should return to zero. The pressure at the service brake bleed screw location should return to the residual pressure held on the brakes by the slack adjuster piston.

The residual pressures at the service brake bleed screw location should be:

785C front: 103 kPa (14.9 psi) 785C rear: 59 kPa (8.6 psi)789C front: 106 kPa (15.3 psi) 789C rear: 65 kPa (9.5 psi)

Low residual pressure may indicate a failed slack adjuster. High residual pressure may also indicate a failed slack adjuster or warped brake discs. To check for warped brake discs, rotate the wheel to see if the pressure fluctuates. If the pressure fluctuates while rotating the wheel, the brake discs are probably warped and should be replaced.

To check for brake cooling oil leakage, block the brake cooling ports and pressurize each brake assembly to a maximum of 138 kPa (20 psi). Close off the air supply source and observe the pressure trapped in the brake assembly for five minutes. The trapped pressure should not decrease.

191

This schematic shows the flow of air through the service/retarder brake air system when the retarder (manual and automatic) is RELEASED, and the service brakes are ENGAGED. Supply air pressure flows from the large service brake air tank to the relay valves and the service brake valve, manual retarder valve, and the ARC valve.

The manual retarder valve and the ARC solenoids block the flow of air. The service brake valve allows air to flow to two double check valves that block the passages to the manual retarder and ARC valves. Air pressure from the service brake valve flows through the double check valves to the service brake relay valve and the front brake oil cooler diverter valve.

The service brake relay valve opens and metered air flows from the large service brake air tank to the brake cylinders. The relay valves reduce the time required to engage and release the brakes. A pair of double check valves above the brake cylinders prevent the flow of service brake air to the ARC relay valve.

Air from the service brake valve also flows to the brake light switch and the service/retarder brake switch. Depressing the service brake pedal turns ON the brake lights and changes the transmission shift points and anti-hunt timer.


��0��

��1��3��

��

1��3��0��$

(��

��+��(��1�(9��(��)��1�(9��(��

(��0��

1��3��!��%��

��+��"��%

��"��%

-� ��1��3��

#��$$��#� ��

When the manual retarder lever is moved, air flows through three double check valves that block the passages to the service brake valve and the ARC valve. Air pressure from the manual retarder brake valve flows through the double check valves to the service brake relay valve and the front brake oil cooler diverter valve.

Air from the manual retarder brake valve also flows to the retarder switch, the brake light switch, and the service/retarder brake switch. Engaging the manual retarder turns ON the retarder dash lamp, the brake lights, and changes the transmission shift points and anti-hunt timer.

When the ARC is activated, air flows through two double check valves that block the passages to the service brake valve and the manual retarder brake valve. Air pressure from the ARC valve flows through the double check valves to the front brake oil cooler diverter valve.

When the ARC brake system is ENGAGED, the ARC relay valve opens and metered air flows from the service brake tank, through a pressure protection valve and the double check valves, to the three brake cylinders. The pressure protection valve prevents a total loss of air pressure in the service brake air system if the ARC relay valve fails. The protection valve opens to send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below 310 kPa (45 psi).

Air from the ARC valve also flows to the retarder switch, the brake light switch, and the service/retarder brake switch. Engaging the ARC turns ON the retarder dash lamp, the brake lights, and changes the transmission shift points and anti-hunt timer.


192

This schematic shows the flow of oil through the 789C brake cooling system. Three pump sections provide oil for rear brake cooling: the two-sections of the hoist pump and the fourth section of the torque converter pump. Two pump sections provide oil for front brake cooling: the torque converter charging and the brake release sections of the torque converter pump. All the pumps pull oil from the hydraulic tank through suction screens.

Oil flows from the hoist pump sections through two screens to the hoist valve. In the HOLD and FLOAT positions, oil from the pump flows through the hoist valve to the rear brake cooling system.

Oil flows from the fourth section of the torque converter pump, joins with the oil from the hoist valve, and flows to the rear brake oil coolers.

Oil from all three pump sections combines and flows through the screens and rear brake oil coolers located on the right side of the engine. The rear brake oil coolers are cooled by the engine jacket water cooling system. From the coolers, oil flows through the brakes and returns to the hydraulic tank.


��1�(9��**!��)��

-� ��

1��3�$

� �;��

� ��

�%��

-��

-� ��1��3��

*��

#��3��1��3��

��$��

��

��

� ��

*��

-��

#��3��

1��3��

-��

��1��3��

*�� $

��1��3�$

*��

��

��

��

� �$��#�&'

� �$��

��$

� �$��

��

The pressure in the rear brake cooling system is controlled by the oil cooler relief valve located in the hoist valve. The relief valve setting is 790 kPa (115 psi).

Oil flows from the torque converter charging pump through the torque converter charging filter, the torque converter, and the torque converter outlet screen to the front brake oil cooler diverter valve.

Oil flows from the brake release pump through the brake release filter to the brake release valve. The brake release valve controls the oil pressure to release the parking brakes, lock up the torque converter and shift the directional spool in the hoist valve. These functions require minimal oil flow. Most of the oil from the brake release pump flows through the brake release valve and joins with the torque converter charging pump oil at the front brake oil cooler diverter valve.

When the service or retarder brakes are ENGAGED, the front brake oil cooler diverter valve allows brake cooling oil to flow through the front brake oil cooler to the front brakes. When the brakes are RELEASED, the oil bypasses the cooler and flows directly to the brakes. The front brake oil cooler is cooled by the engine aftercooler cooling system. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit.

Normally, front brake cooling oil is diverted around the cooler and goes directly to the front brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).

The brake cooling system on the 785C truck is slightly different from the 789C truck. The 785C truck does not have a fourth section on the torque converter pump for rear brake cooling. The parking brake release pump sends oil to the rear brake cooling system, not to the front brake cooling system.


Shown is the left rear brake housing on a 789C truck. Brake cooling oil pressure can be tested at the two taps (arrow) located in the brake cooling oil tubes. One tap is located on the brake cooling inlet tube and another tap is located on the brake cooling outlet tube. The pressure measured at the brake inlet tube (from the oil coolers) will always be higher than the pressure measured at the brake outlet tube.

With the brake cooling oil temperature between 79 to 93°C (175 to 200°F), the pressure measured at the brake inlet tube should be above 14 kPa (2 psi) at LOW IDLE and below 172 kPa (25 psi) at HIGH IDLE.

Four brake oil temperature sensors, one for each brake, are located in the brake oil cooling tubes. The brake oil temperature sensors provide input signals to the VIMS, which keeps the operator informed of the brake cooling oil temperature.

The most common cause of high brake cooling oil temperature is operating a truck in a gear that is too high for the grade and not maintaining sufficient engine speed. Engine speed should be kept at approximately 1900 rpm during long downhill hauls.

Also, make sure the pistons in the slack adjuster are not stuck and retaining too much pressure on the brakes (see Visuals No. 189 and 190).

193


194

BRAKE ELECTRONIC CONTROL SYSTEM

The "C" Series trucks use an additional Electronic Control Module (ECM) for controlling both the Automatic Retarder Control (ARC) and the Traction Control System (TCS).

The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control modules are replaced with one Brake ECM. The Brake ECM controls both the ARC and the TCS functions. The TCS is now on the CAT Data Link, and the Electronic Technician (ET) service tool can be used to diagnose the TCS.

The Brake ECM receives information from various input components such as the Engine Output Speed (EOS) sensor, retarder pressure switch, left and right wheel speed sensors, and the TCS test switch.

Based on the input information, the Brake ECM determines whether the service/retarder brakes should ENGAGE for the ARC or the parking/secondary brakes should ENGAGE for the TCS. These actions are accomplished by sending signals to various output components.


#� ' �� 7�� 8��

��!�&' ��

!��%�

(��''�0��

��%��.%��'��$ �

��# ��*�#*��

* �# ��*�#*��

��*��'��'��$ �

��$&�$$� �+�%�$$�$��

��

�� (��(�(�!��9

(��

!��.%��'��$ �

(��*��+�*��"��%

*��'��

*��'��

��!�&'(��

#��$$��"��%

��#��$$��"��%

��$��"��%

(��

��

(��

��

�%��!��"��%

(��"��%

#��3��+�� 0�1��3��"��%

��$&�$$� ��*��'��'��$ �

��+��1��3��"��%

�%� ��$ �

��'��+��&��

��$ �

1�(9��!��*��*��*!��)��

��

1��3��*��$�� 3��"��%

��*��!��

��-��

#��3��1��3��-��

��-��0

!��1��3��$��#��$$��

��%��1��3��$��#��$$��

��*��&'��$ �

1��3��(��#��$$��

�

��#��$$��

Output components include the ARC supply and control solenoids, the retarder ENGAGED lamp, the TCS selector and proportional solenoids, and the TCS ENGAGED lamp.

The Brake ECM also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores possible diagnostic codes for retrieval at the time of service.

The Engine ECM, the Transmission/Chassis ECM, the Vital Information Management System (VIMS), and the Brake ECM all communicate through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared.

The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used to perform several diagnostic and programming functions.

Some of the diagnostic and programming functions that the service tools can perform are:

- Display real time status of input and output parameters- Display the internal clock hour reading- Display the number of occurrences and the hour reading of the first and last occurrence for

each logged diagnostic code and event- Display the definition for each logged diagnostic code and event- Display the supply and control solenoid engagement counter- Program the ARC control speed- Perform ARC diagnostic tests- Upload new Flash files


The Brake ECM (arrow) is located in the compartment at the rear of the cab. The Brake ECM does not have a diagnostic window like the ARC and the TCS used on the "B" Series trucks.

All diagnostic and programming functions must be performed with an Electronic Control Analyzer Programmer (ECAP) or a laptop computer with the Electronic Technician (ET) software installed. ET is the tool of choice because the Brake ECM can be reprogrammed with a "flash" file using the WinFlash application of ET. ECAP cannot upload "flash" files.

The Brake ECM looks like the Engine ECM with two 40-pin connectors, but the Brake ECM does not have fittings for cooling fluid. Also, the Brake ECM has no access plate for a personality module.

195


196

Automatic Retarder Control (ARC)

The Automatic Retarder Control (ARC) system function is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. The ARC system engages the service/retarder brakes. If the ON/OFF switch is moved to the ON position, the ARC will be activated if the throttle pedal is not depressed and the parking/ secondary brakes are RELEASED. The ARC system is disabled when the throttle is depressed or when the parking/secondary brakes are ENGAGED.

The ARC is not connected to the service brakes and the manual retarder. When the ARC is ENGAGED, air flows from the ARC valve to a separate relay valve located near the brake master cylinders (see Visual No. 182).

The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (engine speed setting is programmable). When the ARC initially takes control of retarding, the engine speed may oscillate out of the ± 50 rpm target, but the engine speed should stabilize within a few seconds.


(�� &��

��''�0��

� ��

(�� #��$$��"��%

��

��!�&'

�(��!��3

(��*��+�*��"��%

*��'��

*��'��

(��-� &��1��3��$��

��1��3��

��

��#��$$��"��%

� ��+��1��3��0��

��

��'��$ �

� �(��0��

1��3��7(��+��8

��$&�$$� ��+��%�$$�$��

��

��

��

( �*�(��(��*��*!

For proper operation of the ARC, the operator needs only to activate the control with the ARC ON/OFF switch and select the correct gear for the grade, load, and ground conditions. The ARC is designed to allow the transmission to upshift to the gear selected by the shift lever. After the transmission shifts to the gear selected by the operator and the engine speed exceeds 1900 rpm, the ARC will apply the retarder as needed to maintain a constant engine speed.

The ARC system also provides engine overspeed protection. If an unsafe engine speed is reached, the ARC will engage the brakes, even if the ARC ON/OFF switch is in the OFF position and the throttle is depressed.

Trucks approaching an overspeed condition will sound a horn and activate a light at 2100 rpm. If the operator ignores the light and horn, the ARC will engage the retarder at 2180 rpm. If the engine speed continues to increase, the Transmission/Chassis ECM will either upshift (one gear only above shift lever position) or unlock the torque converter (if the shift lever is in the top gear position) at 2300 rpm.

The ARC also provides service personnel with enhanced diagnostic capabilities through the use of onboard memory, which stores possible faults, solenoid cycle counts and other service information for retrieval at the time of service.

By using an ECAP or a laptop computer with the Electronic Technician (ET) software installed, service personnel can access the stored diagnostic information or set the adjustable engine speed control setting.

The Auto Retarder Control receives signals from several switches and sensors. The control analyzes the various input signals and sends signals to the output components. The output components are two solenoids and a lamp.

NOTE: The ARC ON/OFF switch must be in the OFF position to run the ARC diagnostic test with ET.

INSTRUCTOR NOTE: For more detailed information about the Automatic Retarder Control (ARC) system, refer to the Service Manual Module "Off-Highway Truck/Tractors Brake Electronic Control System" (Form SENR1503).


Shown is the location of the Engine Output Speed (EOS) sensor (1) that provides the primary input signal used by the ARC. The engine speed information is the main parameter that the Brake ECM uses to control retarding. The engine speed sensor is a frequency sensor that generates an AC signal from the passing flywheel gear teeth.

The EOS sensor also provides an input signal to the Transmission/Chassis ECM for Transmission Output Speed (TOS) ratification and lockup clutch shift time. The Transmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signal to calculate torque converter lockup clutch shift time. This information is then sent to VIMS. The EOS signal is also used for TOS ratification. EOS is compared to the EOS calculated from the TOS and the ratio for the current transmission gear. If the speeds do not agree, the transmission will not downshift. If EOS is less than 1000 rpm the lockup clutch will release. If EOS exceeds 2300 rpm the lockup clutch will release. If EOS exceeds 2500 rpm the transmission will upshift as many gears as necessary to keep engine speed less than 2500 rpm.

The engine speed/timing sensor (2) is also used by the ARC for diagnostic purposes. If the Brake ECM receives an input signal from the engine speed/timing sensor, but not the EOS sensor, the Brake ECM will log an engine speed fault. The ARC will not function without an engine speed signal from EOS sensor (1).

197


1

2

NOTE: The 8T5200 Signal Generator/Counter Group can be connected to the engine speed sensor wiring harness and be used to simulate engine speed for diagnostic purposes. A 196-1900 adapter is required to increase the frequency potential from the signal generator when connecting to the ECM's used on these trucks. To connect the 8T5201 Signal Generator to the engine speed sensor wiring harness, fabricate jumper wires and connect the 8T5198 Adapter Cable (part of the 8T5200 Signal Generator/Counter Group) to the speed sensor harness Deutsch DT connector.

8T5198 Adapter Deutsch DT Connector

Pin B J765 BU Pin 2 (ground)

Pin C 450 YL Pin 1 (signal)


Shown is the location of the retarder pressure switch (1). The retarder pressure switch signals the Brake ECM when manual or automatic retarder air pressure is present. The switch is normally open and closes when the manual or automatic retarder is engaged.

A fault is recorded when the Brake ECM detects the absence of retarder pressure (switch open) while the supply solenoid and the control solenoid are energized.

The auto retarder pressure switch (2) signals the Brake ECM when air pressure is present and the automatic retarder valve (3) is functioning. The auto retarder pressure switch is located in front of the cab in the output port of the automatic retarder valve. The switch is normally closed and opens only when the auto retarder is engaged.

A fault is recorded when the Brake ECM detects the presence of auto retarder pressure (switch open) while the supply solenoid and the control solenoid are not energized.

The supply solenoid valve (4) turns ON or OFF to control the flow of supply air to the automatic retarder valve (3). The Brake ECM energizes the supply solenoid valve with +Battery voltage (24 Volts) at 100 rpm less than the programmed control speed setting. Normally, the reduced speed will be 1800 rpm, since the control speed is set to 1900 rpm at the factory.

A fault is recorded if the Brake ECM senses the signal to the supply solenoid as open, shorted to ground, or shorted to battery.

198


1

2

3

4

5

The control solenoid valve (5) modulates the air flow to the brakes during automatic retarding. The control solenoid receives a Pulse Width Modulated (PWM) signal from the Brake ECM. The longer the duty cycle, the more time the control solenoid valve is open, and more air pressure is allowed to the brakes. Voltage to the control solenoid increases proportionally from zero to approximately 22 Volts with the demand for more brake pressure.

A fault is recorded if the Brake ECM senses the signal to the control solenoid as open, shorted to ground, or shorted to battery.

Normal resistance through the supply and control solenoids is 31 Ohms. An excess resistance of approximately 40 Ohms will prevent the valves from opening and will cause a supply or control valve fault to be logged. Therefore, a measurement of approximately 71 Ohms or more will show that the solenoid is defective.

The Brake ECM can also determine if the solenoid valves have malfunctioned (valves leaking). If air pressure is present at the auto retarder pressure switch when the solenoids are DE-ENERGIZED, the auto retarder pressure switch will signal the Brake ECM that the ARC valve has malfunctioned.


199

Hydraulic Automatic Retarder Control (ARC)

Signal air from the primary air tank flows to the service brake valve and the retarder valve. A shuttle valve, after these valves, then sends the highest signal pressure to the service brake relay valve. The service brake relay valve opens and actuates the brake cylinders with a greater volume of air from the primary air tank.

An addition to the air system is the front brake cooling oil diverter solenoid. Air is supplied to this valve from a smaller secondary air tank behind the cab. The Brake ECM energizes this valve when the service brakes are applied. When the Brake ECM energizes this solenoid, signal air is sent to the diverter valve for the front brake cooling oil. Brake cooling oil is then sent through the cooler for front brake cooling oil.


��0��

1��3��

��

1��3��0��$

��+��(��1�(9��(��)��(��(��

1��3��!��%��+�

��"��%(��#��$$��$ �

-� ��1��3��

-� &�(�� &'��$$ �

-� &�� 0�(��$��

� ��

��4

200

This schematic shows the flow of oil for the ARC system when ENABLED.

The parking brake release pump provides oil flow for the ARC system. The flow continues from the pump, through a check valve to the ARC valve. The ARC valve modulates the amount of pressure to the service brakes in order to control the ground speed of the truck.

The air over hydraulic brake cylinders also use the same service brakes. A shuttle valve between the ARC system and brake cylinders separates these two systems. Whichever system has the greatest pressure, that system will control the service brakes.


#�&'��

� �$��0��3

-� ��1��3�$

#��3��1��3��$��#�&'

��1��3�$

�%��

�%��

(��

�%��3��

(��&��

1��3��0��$

1��3��0��$

�)��( !��(��)��

(��(1!��

-� ��1��3��*�� $

��1��3��*�� $

��0��

��0��

The hydraulic ARC valve (arrow) is located on the left frame rail near the rear differential. This valve contains a supply solenoid valve and a control solenoid valve. A purge solenoid valve is located on the bottom of the ARC valve. The ARC accumulator is located to the right of the ARC valve.

NOTE: The hydraulic ARC valve performs the same functions as the previous air controlled ARC valve. The hydraulic ARC valve use oil pressure instead of air pressure.

201


202

Supply oil from the parking brake release pump flows across a check valve. Oil flow then enters the ARC valve. Hydraulic flow is stopped because the ARC spool is in the blocked position. Hydraulic flow is then directed to the accumulator to charge the accumulator to the same pressure as the parking brake release system pressure. Hydraulic flow is also routed through the supply solenoid valve to apply pilot pressure to the left end of the ARC spool. This pressure will keep the ARC spool in the blocked position.


�)��( !��(��(!��*��+�(��*--

� ��

� ��3

��''�0��

#��

�%��3��

#�&'

(��&��

�' �

� ��1��3�$

203

The Brake ECM supplies current to the supply solenoid. The supply solenoid valve sends pilot oil to the right end of the ARC spool. This pilot oil shifts the ARC spool to the left opening the left side of the ARC spool to tank. At the same time, pump supply oil is directed to the right side of the ARC spool. Now, pump oil is directed to the control solenoid valve.

The Brake ECM will send varying levels of current to the control solenoid. This variable current will modulate the spool within the proportional valve. The level of current is dependent on the brake requirements for the ARC valve to maintain a constant breaking force.

When the control solenoid is energized, the pin moves to the right and pushes against the ball. The ball blocks the pump supply oil from flowing to the drain. Pressure increases in the chamber to the left of the spool to move the spool to the right.

When the spool moves to the right, pump supply oil flows to the service brakes. In order to maintain the correct brake pressure, the Brake ECM will vary the current to the control solenoid to open and close the oil drain port.


�)��( !��(��(!��*��+�(��*�

� ��

� ��3

��''�0��

#��

�%��3��

#�&'

(��&��

�' �

� ��1��3�$

*�

*�

204

No current is supplied from the Brake ECM to the supply solenoid. The supply solenoid valve directs any pressurized oil acting on the ARC spool to flow to the tank. Current is supplied from the Steering Bleed Control to the purge solenoid valve for approximately 70 seconds. This allows the pressure within the accumulator to drain from the accumulator back to the tank.


�)��( !�� (�� (!��*--�+�(��*--

� ��

� ��3

��''�0��

#��

�%��3��

#�&'

(��&��

�' �

� ��1��3�$

*�

205

The introduction of the hydraulic ARC control valve has required a number of additional component changes. The basic function of the new system remains the same as the previous system. The Engine ECM, the Transmission/Chassis ECM, the Vital Information Management System (VIMS), and the Brake ECM all communicate through the CAT DATA Link. Communication between the electronic controls allows the sensors of each system to be shared.


(��

��

��''�0�

� �� #��

� ��

� ��

(��' ��

��

��!�&'�(��!��3

(��*��+�*��

�"��%

*��'��

*��'��

��'��

��$ �

1��3��

7(��+��8

��

� ��

( �*�(��(��*��*!

-� ��1��3��

� ��

� ��

#��3��1��3��

��$��#�&'

� ��3

�� 1��3�$

(�� (��

��1��

� ��

The steering bleed down control (1) is located in the compartment behind the cab. While the steering bleed control is not a new component, the control serves an additional function. The steering bleed control is used to purge the ARC accumulator when the machine is shut down. When the control receives a signal from the key start switch, a timer built into the control will energize the purge solenoid for a period of approximately 70 seconds to purge the ARC accumulator.

206


One of the new components, located in the compartment behind the cab, is the front brake cooling diverter solenoid (arrow). When the ARC is engaged, the Brake ECM energizes this solenoid to send an air signal to shift the brake cooling oil diverter valve. This will route the brake cooling oil through the front brake oil cooler for increased cooling. Normally the brake cooling oil is routed around the front brake oil cooler. This is a 24 V normally closed solenoid valve.

207


Shown is the location of the Engine Output Speed (EOS) sensor that provides the primary input signal used by the ARC. The EOS sensor is a passive (two wire) sensor and is located on top of the flywheel housing. The engine speed information is the main parameter that the Brake ECM uses to control retarding. The engine speed sensor is a frequency sensor that generates an AC signal from the passing flywheel gear teeth.

The EOS sensor also provides an input signal to the Transmission/Chassis ECM for Transmission Output Speed (TOS) ratification and lockup clutch shift time. The Transmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signal to calculate torque converter lockup clutch shift time. This information is then sent to VIMS. The EOS signal is also used for TOS ratification. EOS is compared to the EOS calculated from the TOS and the ratio for the current transmission gear. If the speeds do not agree, the transmission will not downshift. If EOS is less than 1000 rpm the lockup clutch will release.

If EOS exceeds 2300 rpm the lockup clutch will release. If EOS exceeds 2500 rpm the transmission will upshift as many gears as necessary to keep engine speed less than 2500 rpm.

ARC also uses the engine speed/timing sensor for diagnostic purposes. The engine/timing speed sensor is located near the rear of the left camshaft. If the Brake ECM receives an input signal from the engine speed/timing sensor, but not the EOS sensor, the Brake ECM will log an engine speed fault. The ARC will not function without an engine speed signal from EOS sensor.

208


209

Traction Control System (TCS)

The Traction Control System (TCS) uses the rear parking/secondary brakes (spring engaged and hydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tire with better underfoot conditions to receive an increased amount of torque. The system is controlled by the Brake ECM (see Visuals No. 194 and 195).

The Brake ECM monitors the drive wheels through three input signals: one at each drive axle, and one at the transmission output shaft. When a spinning drive wheel is detected, the Brake ECM sends a signal to the selector and proportional valves which ENGAGE the brake of the affected wheel. When the condition has improved and the ratio between the right and left axles returns to 1:1, the Brake ECM sends a signal to RELEASE the brake.

The TCS was formerly referred to as the Automatic Electronic Traction Aid (AETA). The operation of the system has not changed. The main differences are the appearance of the ECM, and the TCS is now on the CAT Data Link. Also, the ECAP and ET Service Tools can communicate with the TCS.


1��3��

7(��+��8

#� ' ��

� ��

��

��

!�&'

��

� ��

!��%

��%��.%��'��$ �

!��.%��'��$ �

��$��

�"��%

��

��

�(��!��3

��+��

1��3��"��%

��$&�$$� ��

*��'��'��$ �

<�=>��

.%��$ �$

��(��*��*��*!��)��

A service/retarder brake switch (see Visual No. 128) provides an input signal to the TCS through the CAT Data Link and performs two functions:

1. When the service brakes or retarder are ENGAGED, the TCS function is stopped.

2. The service/retarder brake switch provides the input signal needed to perform a diagnostic test. When the TCS test switch and the retarder lever are ENGAGED simultaneously, the TCS will engage each rear brake independently. Install two pressure gauges on the TCS valve, and observe the pressure readings during the test cycle. The left brake pressure will decrease and increase. After a short pause, the right brake pressure will decrease and increase. The test will repeat as long as the TCS test switch and the retarder lever are ENGAGED.

The TCS valve has a left and right brake release pressure sensor. A laptop computer with the ET software installed can also be used to view the left and right parking brake pressures during the test discussed above in function No. 2. When the proportional solenoid is ENERGIZED, ET will show 44% when the brake is FULLY ENGAGED.

NOTE: During the diagnostic test, the parking/secondary brakes must be released.

INSTRUCTOR NOTE: For more detailed information about the Traction Control System (TCS), refer to the Service Manual Module "Off-Highway Truck/Tractors Brake Electronic Control System" (Form SENR1503).


Shown is the right rear wheel speed sensor (arrow). The TCS monitors the drive wheels through three input speed signals: one at each drive axle, and one at the transmission output shaft.

The Transmission Output Speed (TOS) sensor (see Visual No. 127) monitors the ground speed of the machine and provides input signals to the TCS through the CAT Data Link. The TCS uses the TOS sensor to disable the TCS when ground speed is above 19.3 km/h (12 mph).

210


The Traction Control System (TCS) valve is mounted inside the rear of the left frame rail. Two solenoids are mounted on the valve.

Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and select either the left or right parking brake. If the selector valve shifts to the left parking brake hydraulic circuit, the control oil is drained. The left reducing spool of the control valve can then shift and engage the parking brake.

The Brake ECM energizes the selector solenoid valve with + Battery voltage (24 Volts). Normal resistance through the selector solenoid is between 18 and 45 Ohms.

The proportional solenoid valve (2) controls the volume of oil being drained from the selected parking brake control circuit. The rate of flow is controlled by a signal from the Brake ECM.

The proportional solenoid receives a current between 100 and 680 mA (or 0 to 12 Volts) from the Brake ECM. The more current that is sent, the more the proportional solenoid valve is open, and more oil pressure is drained from the brakes. Normal resistance through the solenoid is between 12 and 22 Ohms.

The pressure taps (3) or pressure sensors (4) can be used to check the left and right brake release pressures when performing diagnostic tests on the TCS. The pressure at the taps in the TCS valve will be slightly less than the brake release pressure measured at the wheels. The pressure sensors are also used to provide parking brake dragging information to the operator.

211


1 2

33

4 4

212

Shown is the TCS with the engine running and the brakes RELEASED.

When the machine is started:

- Oil flows from parking brake release pump through the brake release oil filter where the flow is divided. One line from the filter directs oil to the parking brake release valve. The other line sends oil to the signal port (right end of signal piston) of the TCS control valve.

- Oil flow to the TCS control valve signal port causes the ball check piston to move to the left and unseat the drain ball check valve. Opening the drain ball check valve opens a drain passage to the hydraulic tank.


#��3��1��3��

��$&�$$� ��'��$ �

��+��

1��3��"��%

��

#� ' ��

��

*��

!��(?��

��%��(?��

��(��*��*��*!��)��7��8�� +1�(9��!�(��

1��%��3

*��'��

��$

��'��

��$

��$��

!�&'

��$��

�"��%

When the operator releases the parking brakes:

- Air pressure is increased at the parking brake release valve forcing the valve spool down.- Parking brake release oil can now flow through the parking brake release valve to the TCS

control valve.- In the control valve, oil closes the parking/secondary ball check valve and flows through

the screen.- Oil flows through the right and left brake control circuit orifices.- Oil flows to the ends of the left and right brake reducing valve spools.- When the control circuit pressure is high enough, the reducing spools shift toward the

center of the TCS control valve and parking brake release oil flows to release the brakes.


213

Shown is the TCS with the engine running and the left brake ENGAGED. When signals from the sensors indicate that the left wheel is spinning 60% faster than the right wheel, the following sequence of events occurs:

- The Brake ECM sends a signal to the selector solenoid valve and the proportional solenoid valve.

- The selector solenoid valve opens a passage between the outer end of the left brake pressure reducing valve and the proportional solenoid valve.

- The proportional solenoid valve opens a passage from the selector solenoid valve to drain. The proportional solenoid valve also controls the rate at which the oil is allowed to drain.

- Control circuit oil drains through the selector valve and enters the proportional valve. The reducing valve spool for the left parking brake shifts and blocks the flow of oil to the

parking brake.- Oil in the left parking brake control circuit begins to drain.- The left parking brake begins to ENGAGE.- The left brake orifice restricts the flow of oil from the parking brake release valve.


#��3��1��3��

��$��"��%

��

#� ' ��

��

*��

!��(?��

��%��(?��

��(��*��*��*!��)��7��8�� +!�-��1�(9��(��

1��%��3

*��'��

��$

��'��

��$

��$&�$$� ��

�'��$ �

��+��

1��3��"��%

��$��

!�&'

When the signals from the sensors indicate that the left wheel is no longer spinning, the following sequence occurs:

- The Brake ECM stops sending signals to the selector solenoid and the proportional solenoid.

- The selector solenoid valve and proportional solenoid valve block the passage to drain and allow the control circuit pressure to increase.

- The left brake reducing valve spool shifts to the center position and blocks the passage to drain.

- Parking brake release oil is directed to the left parking brake and the brake is RELEASED.


OPTIONAL EQUIPMENT

FlexxaireTM Fan

Shown is a 3516B Engine with a FlexxaireTM Fan installed. The FlexxaireTM fan provides full control of air movement through the radiator with an automatically controlled, variable pitch fan. The fan is designed to help control cooling requirements in specific applications such as cold weather and high altitude. The thermostatic controller automatically adjusts the blade pitch to maintain an optimum engine coolant temperature.

With zero-pitch start-up, the air dam effect prevents air flow through the radiator and the engine reaches the recommended operating temperature more quickly. The pitch will vary throughout the day based on the engine cooling temperature and air conditioning requirements. The automatic blade pitch control reduces the horsepower loss when engine cooling is not required.

The 10 fan blades attach to the hub assembly (1). A coolant temperature sensor (2) and an air conditioning pressure sensor (see Visual No. 62) provide input signals to an electronic control box located behind the cab (see next page). The electronic control analyzes the input signals and sends an electrical signal to the actuator (3). The actuator rotates and changes the fan pitch as needed to increase or decrease the engine coolant temperature.

214


1

2

3

The FlexxaireTM Fan electronic control box (1) and the remote display (2) are located in the compartment behind the operator's station. The control box is used to set up and calibrate the Flexxaire™ fan. Remove the cover from the control box and follow the instructions on the label inside the cover.

The FlexxaireTM control box provides many features. The customer must decide which features he wants to use before setting up the system. Some of the features are:

Timed Auto-Purge, Purge Interval Override, Temperature Driven Auto-Purge: Off-highway Trucks normally PULL air through the radiator. For a PURGE to occur, the fan blades rotate and PUSH air through the radiator. Changing air flow direction can help clear debris from the radiator.

Actuator Stall Detection: If the fan pitch actuator encounters excessive resistance (bolt falls into the linkage), the control will sense the increased current and attempt an automatic calibration. If the obstruction continues, as a safety measure, the control will rotate the fan blades to full pitch.

Second Fluid Temperature Control: A second temperature sensor can be installed to control the fan pitch in addition to the engine coolant temperature sensor (brake oil temperature).

215


1

2

3 4

Blaze Blocker: A fire suppression system can provide an input signal to the control that will rotate the fan blades to the NEUTRAL position. In the NEUTRAL position, the fan provides no air flow. Limiting the air flow reduces the amount of oxygen to the fire, and the fire suppressant is not blown from the engine compartment.

The following two FlexxaireTM Fan Controls must be set up properly:

Actuator Limits: This procedure sets the travel limits and the NEUTRAL position of the actuator.

Temperature Set Point Calibration: This procedure sets the temperature range that the controller will try to maintain by changing the fan pitch.

The remote display (2) can be used to change the air flow from PUSH to PULL by depressing the air flow button (3). The nine LED bar display to the right of the air flow button indicates the position of the fan. The bottom four LED's indicate the PULL direction. The center LED indicates the NEUTRAL position. The top four LED's indicate the PUSH direction.

The purge button (4) will start the purge cycle if one has been programmed into the control (optional).

INSTRUCTOR NOTE: More detailed information about the FlexxaireTM Fan System can be found in the Service Manual module "FlexxaireTM Fan Installation And Maintenance Manual" (Form SEBC1152).


216

785D LARGE OFF-HIGHWAY TRUCKS

The 785D Truck is an update to the 785C Large Off-Highway Truck. This presentation shows what is new and different for the "D" series compared to the current production "C" Series truck. Basically the engine is similar to the engine in the "C" Series. The "D" series truck has similar power while equipped with a 3512C HD engine. Along with the engine replacement, the intake manifold air is cooled with an Air To Air Aftercooler (ATAAC). The SCAC pump will now be used as the auxiliary coolant pump which circulate coolant through the steering oil cooler and the front brake oil cooler.

The "D" Series truck will use the folded core radiator which provides the convenience of repairing or replacing smaller individual cores. The "D" model also is equipped with an ATAAC on the both sides of the radiator. The machine components are very similar with the exception of a diagonal ladder across the front of the radiator, an optional Power Assisted Ladder (PAL) (not shown), and with a continuous RAXL filtration again similar to the 793D LOHT.

The load carrying capacity of the truck is between 118 to 136 Metric tons (130 to 150 tons). The Gross Machine Weights (GMW) of the "D" Series trucks is approximately 249480 kg (550000 lb.).


3512C High Displacement Engine

Shown is the 3512C HD engine used in the 785D Large Off-highway Truck. This engine replaces the production Caterpillar 3512B twin turbocharged and coolant aftercooled engine. The new truck will use an ATAAC system to cool the intake manifold.

The controller for the 3512C HD engine will be the ADEM 3 with two seventy pin connectors. This ECM replaces the ADEM 2 with two forty pin connectors that is used on the production 3512B.

These engines utilize the Electronic Unit Injection (EUI) system for power, reliability, and economy with reduced sound levels and low emissions

The 3512C HD engines meet US Environmental Protection Agency (EPA) Tier II Emission Regulations for North America and Stage IIa European Emission Regulations.

217



The 3512C HD engine has the following features.

- Electronic Speed Governing

- Cold Mode Strategy

- Altitude Compensation

- Variable Injection Timing

- Engine Monitoring and Protection

- Optional engine pre-lubrication

These features result in precise speed control, faster cold starting, reduced smoke (under all operating conditions), and electronic engine protection.

The engine performance specifications for the 785D truck are:

- Serial No. Prefix: B7F

- Performance spec: 0K8508

- Max altitude: 4467 m (14000 ft.)

- Gross power: 1081 kW (1450 hp))

- Net power: 1005 kW (1348 hp)

- Full load rpm: 1750 rpm

- High idle rpm: 1937 rpm

- Stall speed rpm: 1672


218

Right Side Engine Components

The following is a list of the engine components located on the right side of the engine. - Right side exhaust temperature sensor (1) - Location for the turbo inlet pressure sensor (2) - Regulator housing (3) - Right side turbo oil lubrication supply (4) - Fuel priming pump and fuel filter (5) - Alternator (6) - Crankcase pressure sensor (7) - Engine oil cooler (8) - Rear brake oil coolers (9) - Fuel transfer pump (10) - Engine coolant flow switch (11) - Coolant S•O•S port (12) - Primary coolant pump (13)

5

1

6

10

4

3

7 8 1211

2

139


219

Engine Components Left Side

The following is a list of the components on the 3512C HD engine. - Left side turbo inlet pressure sensor (1) - Exhaust temperature sensor (2) - Coolant temperature sensor (3) - Left side turbo oil lubrication supply (4) - Fuel fi lter differential switch (5) - Air conditioning Compressor (6) - Fuel fi lter base with fuel priming pump switch (7) - Air compressor (8) - Fuel fi lters (9) - Speed/timing sensor (10) - Auxiliary coolant pump (11) - Engine oil fi lters (on the fi lter base there is a fi ltered and unfi ltered pressure sensor) (12) - Starter location (13) - Engine oil level switch (14)

8

11 12

9

13

7

10

3

14

1

2

56

4

220

Engine Components Front

The following is a list of the components on the 3512C HD engine front. - Regulator housing (1) - Engine ECM (2) - Alternator (3) - Intake manifold pressure sensor (boost) (4) - Atmospheric pressure sensor (5) - Air conditioning Compressor (6) - Primary coolant pump (7) - Air compressor (8)


1

3

2

6

87

4 5

221

Engine Components Rear

The following is a list of the rear components on the 3512C HD engine. - Intake manifold temperature sensor (1) - Right side turbo lubrication connector (2) - Engine speed sensor (3) - Pump drive (4)


12

3 4

222

Turbocharger Location

The following is a turbo list for the 3512C HD engine. - Left front turbo (1) - Right front turbo (2) - Left rear turbo (3) - Right rear turbo (4)


1 2

3 4


��

��

��

��

��

��

��

!"�#��$

%�&�� "'��

(��

��)�"�'��&� ��

%�&��*�+��

��

"�'��&� ��

��

%��!��

�,-./ �0#�%% "��12 � �1"�� 3 "%4�#2!��!4

�

%��*��2�5��./��

"��

��&��"��2��

!�'��

%�&��

"��

%�&��

��

2��$�!��"'��

+��"��2��

��&��"��%6��

+��"��%6��

"��$��

4��%��

%�&��% 4

21�*"

�� !��0��

��$��

*��#+��

7��&��

�*"�*"

��!+��"'��

Engine Electronic Control Module Diagram

The above illustration shows the inputs to and the output from the electronic control system for the 3512C High Displacement (HD) engine. Fuel injection through the Electronic Unit Injectors (EUI) is controlled by the Engine ECM. The Engine ECM in the 785D truck is the ADEM III. The input signals to the Engine ECM are normally through switches, and sensors. The sensor inputs are both analog and Pulse Width Modulation (PWM). The switch inputs are either pressure, flow, level, and contact type.

When the injector solenoids are energized determines the timing of the engine. How long the solenoids are energized determines the engine speed.

The 785D (MSY) truck engines are designed to meet the US Environmental Protection Agency (EPA) Tier II emissions regulations for engines over 1082 gross kW (1450 gross hp). To meet this regulation the 785D (MSY) truck engine will use a new Emission Software. When installing the new Emission Software "flash" files in an Engine ECM, ET can use the American Trucking Association (ATA) Data Link or the CAT Data Link. The ATA and CAT Data Links consist of a pair of twisted wires that connect to the Engine ECM and the diagnostic connector in the cab. The wires are twisted to reduce electrical interference from unwanted sources such as radio transmissions.

223


224

Engine ECM and Atmospheric Pressure Sensor

The illustration above shows the location of the Engine ECM (1) and the atmospheric pressure sensor (2).

The Engine ECM is an ADEM III module and is equipped with two 70 pin connectors. On the ADEM III ECM, J1 is callout (4) and J2 is callout (3).

The Engine ECM (1) is mounted on the front of the engine on the right side of the machine. The engine ECM is accessed from below the machine.

The Engine ECM makes decisions based on control program information in memory, switch inputs, analog input signals, and sensor input signals.

The Engine ECM responds to machine control decisions by sending a signal voltage to the appropriate circuit which creates an action. For example, as the operator depresses the throttle pedal, the Engine ECM interprets the input signal from the throttle pedal position sensor, evaluates the engine status, and sends a signal to the injectors to increase fuel.

The Engine ECM receives three different types of input signals:- Switch input: Provides the signal line to battery, ground, or open.- PWM input: Provides the signal line with a square wave of a specific frequency and a

varying positive duty cycle.- Speed signal: Provides the signal line with either a repeating, fixed voltage level pattern

signal or a sine wave of varying level and frequency.

3 4

21


The Engine ECM has three types of output drivers:

- ON/OFF driver: Provides the output device with a signal level of +Battery voltage (ON) or less than one Volt (OFF).

- PWM solenoid driver: Provides the output device with a square wave of fixed frequency and a varying positive duty cycle.

- Controlled current output driver: The ECM will energize the solenoid with 1.25 amps for approximately one half second and then decrease the level to 0.8 amps for the duration of the on time. The initial higher amperage gives the actuator rapid response and the decreased level is sufficient to hold the solenoid in the correct position. An added benefit is an increase in the life of the solenoid.

The Engine ECM receives signals from the speed timing sensors, oil level switch, coolant flow switch, exhaust temperature sensors, coolant temperatures sensors, engine pressure sensors, and the current engine operating status. The Engine ECM interprets signals and determines the appropriate output signals to the engine. Different conditions of the inputs affect the output conditions.

The Engine ECM communicates through the CAT Data Link. The CAT Data Link allows high speed proprietary serial communications over a twisted pair of wires. The CAT Data Link allows different systems on the machine to communicate with each other and also with service tools such as Caterpillar Electronic Technician (ET).

The Engine ECM has built-in diagnostic capabilities. As the Engine ECM detects a fault condition developed by the engine, the ECM logs the faults in memory and displays them on the VIMS. The fault codes can also be accessed using the ET service tool.

NOTE: Engine ECM faults displayed on the VIMS relating to the Engine ECM will have a Module Identifier (MID) of "36." For more information, refer to the Service Manual module "Engine, Systems Operation Testing and Adjusting"


The following is a list of Diagnostic Codes for the Engine ECM

- MID 036 - CID 0168 - FMI 01 - System voltage - data below normal range

- MID 036 - CID 0168 - FMI 02 - System voltage - incorrect signal

- MID 036 - CID 0253 - FMI 11 - Personality Module - mechanical failure

- MID 036 - CID 0261 - FMI 13 - Engine timing - out of calibration

- MID 036 - CID 0262 - FMI 03 - 5 Volt DC supply - short/open to + Batt

- MID 036 - CID 0262 - FMI 04 - 5 Volt DC supply - short to ground

- MID 036 - CID 0263 - FMI 03 - Digital sensor voltage - short/open to + Batt

- MID 036 - CID 0263 - FMI 04 - Digital sensor voltage - short to ground

- MID 036 - CID 0267 - FMI 02 - Incorrect engine shutdown switch input - incorrect signal

- MID 036 - CID 0268 - FMI 02- Check programmable parameters - incorrect signal

- MID 036 - CID 0800 - FMI 09- Unable to communicate with VIMS - abnormal update

Atmospheric Pressure Sensor

The atmospheric pressure sensor is located behind the Engine ECM on the right front of the engine. The Engine ECM uses the atmospheric sensor as a reference when calibrating the pressure sensors. The sensor receives a regulated 5.0 ± 0.5 Volts from the ECM. The sensor output is a DC signal that varies between 0.3 and 4.8 VDC with an operating pressure between0 and 111 kPA (0 and 15.7 psi). When troubleshooting an analog sensor, connect a multimeter between pin B and Pin C of the sensor connector. Set the meter to read "DC Volts." The DC Voltage should read between 0.2 and 4.8 VDC.

Also, the Engine ECM uses the atmospheric pressure sensor to derate the fuel delivery at a high elevations (altitudes). At 14,000 feet, the atmospheric pressure data that is sent to the Engine ECM will initiate a derate 1%. The fuel delivery will be derated 1% per 1 kPa up to 20% derate. If the Engine ECM detects a fault for the atmospheric pressure sensor, the fuel delivery will be derated to 20%. If the Engine ECM detects an atmospheric sensor and a turbocharger inlet pressure sensor fault at the same time, fuel delivery will be derated to 40%.

The following is a list of Diagnostic Codes for the atmospheric pressure sensor.

- MID 036 - CID 0274 - FMI 03 - Atmospheric Pressure Sensor - Short/open to + Batt

- MID 036 - CID 0274 - FMI 04 - Atmospheric Pressure Sensor - Short to Ground

- MID 036 - CID 0274 - FMI 13 - Atmospheric Pressure Sensor - out of calibration


Shown is the top of a cylinder head with the valve cover removed. The most critical output from the Engine ECM is the signal to the Electronic Unit Injection (EUI) solenoid (arrow). One injector is located in each cylinder head. The Engine ECM analyzes all the inputs and sends a signal to the injector solenoid to control engine timing and speed.

Engine timing is determined by controlling the start time that the injector solenoid is energized. Engine speed is determined by controlling the duration that the injector solenoid is energized.

3500 injectors are calibrated during manufacturing for precise injection timing and fuel discharge. After the manufacturer's calibration, a four-digit "E-trim" code number is etched on the injector tappet surface. This E-trim code identifies the injector’s performance range. Load the code etched on the injector to the personality module (software) of the Engine ECM using the ET service tool. The software uses the trim code to compensate for the manufacturing variations in the injectors and allows each injector to perform as a nominal injector.

When an injector is serviced, the new injector’s trim code should be programmed into the Engine ECM. If the new trim code is not entered, the previous injector’s characteristics is used. The engine will not be harmed if the new code is not entered, but the engine will not provide peak performance. On the following page there is a list of the diagnostic codes for each injector solenoid.

NOTE: No. 1 injector is located on the front right side of the engine and No. 2 injector is located on the front left side of the engine. The odd number injectors is on the right side and the even number injectors is on the left side.

225


The following is a list of the injector Diagnostic Codes in the 3512C HD Engine.

- MID 0036 - CID 0001 - FMI 05 Cylinder #1 Injector coil - open circuit- MID 0036 - CID 0001 - FMI 06 Cylinder #1 Injector coil - short circuit

- MID 0036 - CID 0002 - FMI 05 Cylinder #2 Injector coil - open circuit- CID 0036 - CID 0002 - FMI 06 Cylinder #2 Injector coil - short circuit

- MID 0036 - CID 0003 - FMI 05 Cylinder #3 Injector coil - open circuit - MID 0036 - CID 0003 - FMI 06 Cylinder #3 Injector coil - short circuit










- MID 036 - CID 1495 - FMI 02- Injector codes not programmed - incorrect signal


226

Primary Speed/Timing Sensor

The primary speed timing sensor (arrow) is located near the rear of the engine on the left side. The sensor is mounted in the housing for the camshaft gear. The sensor sends the speed, direction, and the position of the camshaft data to the Engine ECM by counting the passing teeth and measuring the gaps between the teeth on the timing wheel that is mounted on the camshaft. The primary speed timing sensor receives has a 12 VDC input from the Engine ECM.

If the Engine ECM does not receive an input signal from the sensor, the engine will not start.

The following is a list of the Diagnostic Codes for the speed/timing sensor:

- MID 036 - CID 0190 - FMI 02 - Loss of engine Speed Signal

- MID 036 - CID 0274 - FMI 03 - Engine Speed - Short to + Battery

- MID 036 - CID 0274 - FMI 08 - Engine Speed - Signal abnormal


Engine Speed Sensor

A passive (two wire) engine speed sensor (arrow) is positioned on top of the flywheel housing. The passive speed sensor uses the passing teeth of the flywheel to provide a frequency output. The passive speed sensor sends the engine speed signal to the Transmission ECM and the Brake ECM. The signal from the passive speed sensor is used for the Automatic Retarder Control (ARC) engine control speed, shift time calculations, and transmission output speed (TOS) calculations.

227


Coolant Temperature Sensor

The coolant temperature sensor (1) is located in the thermostat (regulator) housing (2) on the left side of the engine. The sensor sends the temperature data to the Engine ECM. Then, the ECM sends the temperature data to the VIMS module which relays the information to the VIMS message center.

The Engine ECM uses the coolant temperature sensor information for cold mode functions such as timing changes, elevated idle, cold cylinder cut-out, ether injection, and others.

The following is a list of the Diagnostic Codes for the coolant temperature sensor:

- MID 036 - CID 0110 - FMI 03 - Engine coolant temperature sensor - open/short to +bat

- MID 036 - CID 0110 - FMI 04 - Engine coolant temperature sensor - short to ground

If the coolant temperature increases above 107° C (226° F), the Engine ECM will log an event that requires a factory password to clear.

228

2

1


Coolant Flow Switch

Coolant flows from the jacket water pump, past the coolant flow warning switch (1), and through the various system oil coolers (engine oil, torque converter/transmission, and rear brake).

The coolant flow switch sends an input signal to the Engine ECM. The Engine ECM sends the signal to the VIMS, which in turn informs the operator of the coolant flow status.

If the ECM detects a low coolant flow condition, a low coolant flow event will be logged. A factory password is required to clear this event.

Also shown is the coolant S•O•S port (2).

229

21


230

Crankcase Pressure Sensor

The crankcase pressure sensor (arrow) is located on the right side of the engine above the engine oil cooler. The crankcase pressure sensor provides an input signal to the Engine ECM. The ECM provides the signal to the VIMS, which informs the operator of the crankcase pressure.

High crankcase pressure may be caused by worn piston rings or cylinder liners.

If crankcase pressure exceeds 3.6 kPa (.5 psi) or 14.4 inches of water, a high crankcase pressure event will be logged. No factory password is required to clear this event.

The following is a list of the Diagnostic Codes for the crankcase pressure sensor:- MID 036 - CID 0110 - FMI 03 - Engine coolant temperature sensor - open/short to +bat

- MID 036 - CID 0110 - FMI 04 - Engine coolant temperature sensor - short to ground

Turbo Inlet Pressure Sensors (Taken on the truck)

The following is a list of the Diagnostic Codes for the left turbo inlet pressure sensor:- MID 036 - CID 0276 - FMI 03 - Left turbo inlet pressure sensor - open/short to +bat- MID 036 - CID 0276 - FMI 04 - Left turbo inlet pressure sensor - short to ground

The following is a list of the Diagnostic Codes for the right turbo inlet pressure sensor:- MID 036 - CID 0275 - FMI 03 - Right turbo inlet pressure sensor - open/short to +bat- MID 036 - CID 0275 - FMI 04 - Right turbo inlet pressure sensor - short to ground

231


232

1

2


The 3512C Engine ECM logs several data events that could cause damage to the engine. Some of the events require factory passwords to clear from the ECM memory. The events logged by the Engine ECM, their maximum derate, and their trip points are listed below:

Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%. Factory password required.


Intake Manifold Air Temperature Sensor

The intake manifold temperature sensor is located at the rear of the engine in the intake manifold. This sensor is a intake manifold air temperature to the Engine ECM.

The following are the Diagnostic Codes for the intake manifold air temperature sensor.

- MID 36 - CID 0179 - FMI 03 Intake manifold temperature sensor - open/short to +batt- MID 36 - CID 0179 - FMI 04 Intake manifold temperature sensor - short to ground

An E279 event will initiate and log a Level 2 derate if the intake manifold air temperature is above 107° C (224° F).

Intake manifold air temperature can be high for the following reasons:

- High ambient air temperature

- High inlet air restriction and/or high altitude

- Restriction in the exhaust system

- Faulty inlet air temperature sensor and/or circuit

- Faulty ATAAC

- Faulty fan

233


Intake Manifold Pressure Sensor (Boost)

The intake manifold pressure sensor (arrow) is located in the Y-pipe monitoring the air pressure from the ATAAC. Shown is the turbocharger outlet pressure sensor. The turbocharger outlet pressure sensor sends an input signal to the Engine ECM. The Engine ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure.

The best way to check for a power problem is to compare the truck performance with the rimpull charts in the performance handbook (SEBD0340). The truck should be able to climb a grade in the same gear as specified in this publication.

If an engine power problem is suspected, check boost pressure at full load rpm. If boost pressure is correct at full load rpm, the engine is not the problem and other systems such as the torque converter should be checked.

To check boost pressure at full load rpm, the truck must be operated in FIRST GEAR with the throttle at MAXIMUM and the retarder gradually engaged. Traveling up a grade is best as long as the engine rpm does not fall below the full load rpm specification during the test. Gradually engage the retarder until the full load rpm is displayed. When the full load rpm is displayed, record the boost pressure. If boost pressure is within the specifications at full load rpm, the engine is operating correctly.

234


Use ET or the VIMS display panel to view the engine rpm and boost pressure. The boost and full load rpm specifications are:

Engines with no series turbochargers or wastegate:

- Boost Pressure: Approximately 178 kPa (25 psi)- Full load rpm: Approximately 1672 rpm

Generally, Torque Converter (TC) stall speed (in gear, full throttle, zero ground speed) is used to determine if the engine power is low or a torque converter problem exists. For example, if the engine power is within specification and the stall speed is high, the torque converter may have a problem (low internal oil pressure, poor internal tolerances, or damaged components).

Since the torque converter stall rpm is very close to the full load rpm, the boost pressure at torque converter stall will be very close to the full load boost specifications.

- Torque Converter Stall rpm: approximately 1672 rpm

The following are the Diagnostic Codes for the intake manifold pressure sensor.- MID 36 - CID 0273 - FMI 03 Intake manifold temperature sensor - open/short to +batt- MID 36 - CID 0273 - FMI 04 Intake manifold temperature sensor - short to ground

Below is a list of possible causes for boost pressure below normal.

- Fuel supply (Possible restriction and/or air in fuel supply)- Injector solenoid (Active codes)- Engine speed/timing signal (Ensure no 190 - 08 Diagnostic Code)- Active engine derate (Check for other active engine derate)- Intermittent sensor problem (Check for logged codes)- Air Inlet Restrictions (Check for restrictions)- ATAAC system air leak(s) (Check for leaks)

236

235

Left And Right Side Exhaust Temperature Sensors

The exhaust temperature sensors are located in the exhaust manifold that is attached to the inlet of the turbine section of the turbo. The sensors monitor the exhaust temperature and send the results to the Engine ECM. This sensor sends data to the Engine ECM with a Pulse Width Modulated (PWM) signal.

The following is a list of the Diagnostic Codes for the Exhaust Temperature Sensors.- MID 0036 - CID 0827 - FMI 08 Left Exhaust Temperature Sensor - signal abnormal- MID 0036 - CID 0828 - FMI 08 Right Exhaust Temperature Sensor - signal abnormal

1

2



An E021 event will initiate and log a Level 2 Derate if the exhaust temperature is above 750° C (1382° F) for five seconds. The Engine ECM will derate the fuel delivery 2% for every 15 second interval with a maximum derate of 20%.

- Left side exhaust temperature sensor (1)- Right side exhaust temperature sensor (2)

Probable Causes

-Air inlet and exhaust system (Air inlet restrictions, exhaust restrictions, and any leaks in the ATAAC tubing)

- Fuel injectors (Excessive amount of fuel is dispersed by the injectors)

- Aftercooler (Blocked air flow through the ATAAC)

- Accessory equipment (parasitic loads on the engine through either the flywheel and/or the damper)


237

Fuel Filter Differential Switch

The fuel filter differential switch (1) is located in the housing for the secondary fuel filters (2). This switch monitors the restriction of fuel through the filters and fuel system. When the pressure differential is approximately 148.9 kPa (21.5 psi) for 30 seconds the switch opens, the Engine ECM will see the fuel restriction trip point and an E095 Event will be logged. Then, a Level 1 Warning will be initiated.

No factory password is required after the fuel restriction is repaired and the differential fuel pressure in the system is below the de-actuation pressure of 69 kPa (10 psi).

Probable Causes

- Plugged fuel filters

1

2


Filtered And Unfiltered Engine Oil Pressure Sensors

Oil flows from the engine oil cooler to the oil filters on the left side of the engine. The oil flows through the filters and enters the engine cylinder block to clean, cool, and lubricate the internal components and the turbochargers.

The engine has two oil pressure sensors. One sensor is located on each end of the oil filter base. The front sensor (2) measures engine oil pressure before the filters. This sensor is located above the fast fill adapter (3). The rear sensor (1) measures oil pressure after the filters. The sensors send input signals to the Engine ECM. The ECM provides the input signal to the VIMS, which informs the operator of the engine oil pressure. Used together, the two engine oil pressure sensors inform the operator if the engine oil filters are restricted.

238

239

2 3

1


The following is a list of the Diagnostic Codes for the engine oil pressure Sensor (unfiltered).- MID 0036 - CID 0542 - FMI 03 Unfiltered oil pressure Sensor - open/short to + batt- MID 0036 - CID 0542 - FMI 04 Unfiltered oil pressure Sensor - short to ground

The following is a list of the Diagnostic Codes for the engine oil pressure Sensors (filtered).- MID 0036 - CID 0543 - FMI 03 Filtered oil pressure Sensor- open/short to + batt- MID 0036 - CID 0543 - FMI 04 Filtered oil pressure Sensor - short to ground

An E073 event will initiate when the pressure differential between the filtered and unfiltered pressure is equal or greater than 69 kPa (10 psi). No factory password is required to clear the event.

An E074 event will initiate when the pressure differential between the filtered and unfiltered pressure is equal or greater than 200 kPa (29 psi). A factory password is required to clear the event.

Probable Causes of a 073 Event and/or a 074 Event are:

- Restricted engine oil filters

A bypass valve (not shown) for each filter is located in each oil filter base.

,-./ ��%#�%8%1"

��!�� %�&��

�

�� 0�&�� $��

�

��0�&�� "'��

�

��%�&�� *��#+��

�

��

�

�� "'��

�

��0�&��%6��"'�� 0�&��2��$�4��+��"'��

The 3512C Engine ECM logs several data events that could cause damage to the engine. Some of the events require factory passwords to clear from the ECM memory. The events logged by the Engine ECM, their maximum derate, and their trip points are listed below:

Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%. Factory password required.

If the atmospheric and turbo inlet pressure sensors both fail at the same time, a derate of 40% will occur.

Low oil pressure: From less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE. Factory password required.

High coolant temperature: Greater than 107° C (226° F). Factory password required.

Engine overspeed: Engine speed is greater than 2200 rpm. Factory password required.

240



Oil fi lter restriction: Greater than 70 kPa (10 psi). No factory password required. Greater than 200 kPa (29 psi). Factory password required.

Fuel fi lter restriction: Greater than 138 kPa (20 psi). No factory password required.

Exhaust temperature high: Greater than 750° C (1382° F). Maximum derate of 20%. Factory password required.

Intake manifold temperature high: Greater than 107° C (226° F). Maximum derate of 25%. Factory password required.

Engine oil level low: No factory password required.

Crankcase pressure high: Greater than 3.6 kPa (.5 psi) or 14.4 inches of water. No factory password required.

Coolant flow low: Factory password required.

User defined shutdown: The customer has the option of installing systems that will shut down the engine if desired. If the installed system sends a ground signal to the Engine ECM at connector J1 pin 19, a user defined shutdown will occur. Factory password required.

The VIMS will shut down the engine for any of the following conditions:- Engine oil level low

- Engine oil pressure low

- Engine coolant temperature high

- Engine coolant level low

- Aftercooler coolant level low

The engine will only shutdown when the shift lever is in NEUTRAL, ground speed is zero, and the parking brake is ENGAGED. The Engine ECM does not log events for VIMS initiated engine shutdowns.

Prelube override: Override the engine oil prelube system with the key start switch. Factory password required.

3 "%4 � �1"��%#��3�%1�21%�% 4

��%��2�5��

�� %�&��%��2��

��

��%�&��

��%�&��

��%6��0�&��

��%�&�� '

241

The Engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the Engine ECM are:

Ether Injection: The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console. The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10° C (50° F) and engine speed is below 1900 rpm.

Cool Engine Elevated Idle: The Engine ECM provides an elevated engine idle speed of 1600 rpm when the engine coolant temperature is below 60° C (140° F). The rpm is gradually reduced to 1000 rpm between 60° C (140° F) and 71° C (160° F). When the temperature is greater than 71° C (160° F), the engine will operate at low idle (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or step on the throttle momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes.



Cold Cylinder Cutout: The 3512C engine uses a cold cylinder cutout function to:

- Reduce white exhaust smoke (unburned fuel) after start-up and during extended idling in cold weather

- Minimize the time in Cold Mode

- Reduce the use of ether injection.

After the engine is started and the automatic ether injection system has stopped injecting ether, the Engine ECM will cut out one cylinder at a time to determine which cylinders are firing. The ECM will disable some of the cylinders that are not firing.

The ECM can identify a cylinder which is not firing by monitoring the fuel rate and engine speed during a cylinder cutout. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cutout to determine if the cylinder is firing.

Disabling some of the cylinders during Cold Mode operation will cause the engine to run rough until the coolant temperature increases above the Cold Mode temperature. This condition is normal, but the operator should be aware it exists to prevent unnecessary complaints.

Engine Start Function: The Engine Start function is controlled by the Engine ECM and the Transmission/Chassis ECM. The Engine ECM provides signals to the Transmission/Chassis ECM regarding the engine speed and the condition of the engine pre-lubrication system. The Transmission/Chassis ECM will energize the starter relay only when:

- The shift lever is in NEUTRAL.

- The parking brake is ENGAGED.

- The engine speed is zero rpm.

- The engine pre-lubrication cycle is completed or turned OFF.

��"��$

��"��+��'�

��'��

��

��0��

��0��

��&��

��'��&��'�� ).9!��$�

��0��

��

%�&��$

%�&��

��'��&��'��

,-./ �0#�%1�21%��*%� 3 "%4

��#�++��

�

%�&��% 4

%�&��

��

4��&��5��

0�&��

%��0��

Fuel System Diagram

Fuel is drawn from the tank through an optional fuel heater, and through the primary fuel filter by the fuel transfer pump (a fuel/water separator can be installed the primary fuel filter). Then, fuel flows from the fuel transfer pump to the secondary fuel filters.

Fuel flows from the secondary fuel filter base to the fuel injectors in the cylinder heads. Unused fuel returns from the injectors and flows through the fuel pressure regulator. As the pressure builds above the regulator pressure, the regulator opens and flow is directed back to the fuel tank. Return oil is sent through the fuel heater.

The secondary fuel filter has a fuel pressure differential switch installed at the outlet of the filter base which monitors the restriction in the secondary fuel filters. This switch is an input to the Engine ECM warning the ECM of an E095 Event "Fuel Filter Restriction."

242



243

244

The fuel priming pump is used to fill the filters after they are serviced. The fuel priming pump (1) has changed location from the previous information in this manual. The pump is now located on the right side of the engine in the fuel priming pump filter base (2). The filter base along with the fuel transfer pump is located above the fuel transfer pump (3). Also shown is the engine oil cooler (4).

The fuel priming pump is electrically controlled with a toggle switch (5) on the secondary fuel filter base (shown in the lower illustration). The fuel priming switch circuit is protected with a 10 Amp breaker (6). Also shown is the location of the fuel differential pressure switch (7).


12

3

5

4

67

245

Fuel flows through the system to the EUI fuel injectors. Return fuel from the injectors flows through the fuel pressure regulator (arrow) before returning to the fuel tank. The fuel pressure in the system is controlled through the fuel pressure regulator. The fuel pressure should between 380 kPa (55 psi) and 621 kPa (90 psi).



��"��$

��"��+��'�

��'��

��

��0��

��0��

��&��

��'��&��'�� ).9!��$�

��0��

��

%�&��$

%�&��

��'��&��'��

,-./ �0#�%1�21%��*%��2421�� 3 "%4

��#�++�� %�&��

��

4��&��5��

0�&��

%��0�� %�&��% 4

246

Fuel System Diagram (Fuel Priming)

Normally, after a filter change or a repair is made to the fuel system, it will be necessary to prime the fuel system (remove air). The fuel priming system will be manually initiated by activating the fuel priming pump switch. At this time, current is sent to the fuel priming pump and the pump rotates and draws fuel from the tank and primary fuel filter. The fuel is directed to the fuel transfer pump. At the pump, fuel is blocked from passing through the fuel transfer pump and is pulled through the fuel priming pump filter and directed over the check valve to the secondary fuel filters (priming fuel is blocked at the fuel transfer pump). From the secondary fuel filters, the fuel flow through the system is similar to normal operation in the fuel system.

NOTE: If the fuel system requires priming, it may be necessary to block the fuel return line during priming in order to force the fuel into the injectors.


247

Top Center Position

The timing bolt is located on the flywheel housing on the right rear of the engine.

This illustration shows the location of the timing bolt (1) and the access cover (2) for the turning tool. Use the Engine Turning Tool (9S-9082) to rotate the engine flywheel.

NOTE: Always turn the flywheel in the counterclockwise direction looking at the flywheel.

1

2


248

Steering And Front Brake Oil Cooling System

The previous 3500 engine used the Separate Circuit AfterCooler pump to supply coolant to cool the aftercooler on the production "C" Series 785 Truck. Now, this pump used on the "D" Series truck with the 3512C HD engine supplies coolant to the steering oil cooler and the front brake cooler. The pump is not shown in the transparent graphic because it is shrinkwrapped with the engine. Coolant supplied by the auxiliary pump is used to cool the air compressor (not shown).

The following is a list of the components in the steering and front brake oil cooling system.

- Steering oil cooler (1)

- Front brake oil cooler (2)

- Outlet tube for the radiator (3)

- Radiator top tank (4)

- Auxiliary coolant tank (5)

1

2

3

4

5


!�6��

��'�

!�� '��

��$�

��

!�6��

��"��$

��

"��

�"��$

"��

��&� ��'��'�

��&� ��'

��'�

��$�

��&

"��

��$�

��&

��&��

�0�&��

�/��0�&��

��

��

�4��&��5��

��

!�

#�

2�

!�

"�

��

�

"%%�21��2�!1#��1"��!(%��2� ��21�� 3 "%4

249

This illustration is a schematic for the steering and front brake oil cooling system. In this system, the auxiliary coolant pump draws coolant from the radiator outlet tube and directs the coolant through the tube to the steering oil cooler and then the front brake oil cooler. From the front brake oil cooler the coolant is returned to the radiator top tank. Coolant from the auxiliary coolant tank supplies coolant to the auxiliary coolant pump inlet to replenish the coolant due to a drop in the coolant level.

The air compressor (not shown) is connected to the auxiliary coolant pump outlet and the return coolant is sent back to the inlet of the pump.

4�++��

!�

"�

!�

!�

!�

"�

!�

!�

��'�!��

2��$ %6��

2��$�4��+��

+��"��&�

+��"��&�

��&��"��&�

��&��"��&�

0��!��

��!��

�'��!��

��!��

4�� '��

��'�!��

,-./ �0#�!2��21#* "2�1�!1#�%:0!* "� 3 "%4

Air Induction And Exhaust System "D" Series Truck

The illustration is a schematic showing the air fl ow from the air fi lters to the muffl ers. Air is drawn into the air cleaner group, passing through the precleaner and the air fi lter (not shown), and the clean air passes out of the air cleaner group through the tube. Then, air fl ows into the divider tube (violet) and into the turbocharger compressor inlet. Air fl ows out of the compres-sor, into the divider tube, and into the ATAAC inlet. This engine is equipped with an ATAAC on each side to cool the intake air supply.

From the ATAAC, cooled air fl ows through the lower tube and up into the Y-tube which is bolted to the air inlet cover for the intake manifold. Then, the air is directed through the manifold. The manifold has twelve elbows, air fl ows to each cylinder on the intake stroke to aid along with the fuel for combustion.

From the aftercooler at the exhaust stroke, hot air fl ows to the turbocharger turbine inlet and out of the turbo through the outlets. The hot air is then directed to a Y pipe which is connected to one muffl er.

250



The turbo bearings are lubricated by the fl ow of engine oil. The turbo bearing lubricating oil for the left side is supplied from the outlet at the left front of the engine at the engine oil fi lter outlet. This supply provides oil to the two left side turbos. The supply for the right side lubricating oil comes from turbo supply (located at the right rear of the engine) and is directed to the right side turbos and then back to the engine oil reservoir.

Air leaks in the ATAAC system normally will cause the exhaust temperatures to increase above the normal operating temperatures. The exhaust temperatures can be monitored through VIMS with Advisor or Caterpillar ET.


3512C HD Engine With ATAAC

The upper illustration shows the air flow to the inlet of the ATAAC.- Air cleaners (1)- Air cleaner tube (2)- Compressor in Y-tube (3)- Compressor out Y-tube (4)- ATAAC (5)- ATAAC outlet tube (6)

The lower illustration shows the flow to the intake manifold from the ATAAC- Air inlet cover (7)

252

251

1

2

3

5

4

6

7


#�++��0��&

+��#��

��&��#��

#�++��

#�++��

;<-#��%!��!:%�*��2 !"2�1

��!:�4��

��!:��'�

�#��2

"�� &��

��+�8��

��'� ��&��'�

��+�8��

� ��8��

�&��%�'��

��+��

��&�"��$

��

=��8��

��8��

�!:��#��8��

�!:��'��#��#��8��

#�++��

"

#�++��"'��

#�++��

253

785D Truck Rear Axle Lubrication (RAXL)

The 785D pilot truck will be equipped with a new Rear Axle Lubrication (RAXL) system. The pump for the new RAXL has been removed from inside the banjo and installed on the outside of the differential housing. This system does not require that the truck be moving in order to provide flow, so the flow can be controlled according to the current conditions. This system will filter while lubricating the rear axle and left/right final drives.

In the upper illustration, the RAXL is shown to be OFF because of cold oil temperature in the differential. When the engine is running and the differential oil temperature is below 13° C (55° F) the Brake ECM sends current to energize the RAXL pump drive oil diverter valve solenoid. The solenoid valve blocks steering oil. The oil that would have been directed to the RAXL motor is returned to the steering tank. At this time, no lubrication oil is displaced and the Brake ECM sends a message to the Chassis/Transmission ECM to limit transmission upshifting.

254

"D" Series RAXL Filtration (Warm Oil)

This illustration shows the schematic for the rear axle lubrication system with the differential oil temperature above 13° C (55° F).

In the RAXL system, the steering pump supplies oil to the steering valve and then on to the RAXL pump drive oil diverter valve. Once the steering system demands are met and the pressure builds to 18600 kPa (2650 psi) in the RAXL pump drive diverter valve, the sequence valve opens and sends approximately 6.9 L/min oil flow through the flow control valve to the solenoid valve.

With the solenoid de-energized, oil flows through the solenoid valve to the RAXL motor. The rotation of the RAXL motor drives the RAXL pump sending fl ow fi rst to the differential lube oil fi lter, and then to the RAXL fi nal drive bypass valve. The oil fl ow through the RAXL motor returns to the tank.


#�++��0��&

+��#��

��&��#��

#�++��

#�++��

;<-#��%!��!:%�*��2 !"2�1

��!:�4��

��!:��'�

7!�4��2

"�� &��

��+�8��

��'� ��&��'�

��+�8��

� ��8��

�&��%�'��

��+��

��&�"��$

��

=��8��

��8��

�!:��#��8��

�!:��'��#��#��8��

#�++��

"

#�++��"'��

#�++��


On the RAXL fi nal drive bypass valve, the following components are installed:- Solenoid valve- Relief valve- Orifice- Logic element

The solenoid valve controls the movement of the logic element and allows lube oil flow to both the final drives and the differential bevel gear, or bypass the final drives. The orifice regulates an equal amount of lube oil flow through the differential and the final drives. The RAXL strategy prevents the final drives from receiving excessive amount of oil flow under certain temperature conditions. The tubes to the final drives and bevel gear contain orifices that balance the oil flow throughout to each final drive.

Differential Lube Oil Pressure Sensor: The differential lube oil pressure sensor is used to sense the pressure in the RAXL system after the filter. The sensor is located on the RAXL filter base. This sensor is PWM pressure sensor that monitors the lube oil pressure in the RAXL system and sends the pressure data back to the Brake ECM. This sensor data is also used by the Transmission ECM for the transmission shifting control strategy.

Differential Oil Temperature Sensor: The differential oil temperature sensor is used to sense the temperature of the oil in the rear axle. It is located on the rear left of the differential housing next to the oil level switch. The temperature sensor produces a PWM signal This temperature sensor monitors the oil temperature in the differential and sends the temperature data back to the Brake ECM.

Differential Oil Filter Pressure Switch: The differential oil filter bypass switch is used to monitor restriction in the filter. If the filter becomes plugged, the switch sends a signal to the Brake ECM indicating the filter is plugged and that the filter requires changing. The switch is located on a filter base which is attached to the RAXL fi nal drive bypass valve. The switch should have a normally closed status and should have the contacts open when the filter is plugged.

RAXL Final Drive Bypass Solenoid Feedback: The RAXL final drive bypass solenoid feedback is used to read the status of the voltage being applied to the final drive bypass solenoid. It is needed because the final drive bypass solenoid is being operated from an Open Collector output driven by a relay. The Brake ECM cannot directly read the status of the relay output without feedback. It will be read by the Brake ECM. The fi nal drive bypass solenoid is used to direct oil fl ow away from the fi nal drives. When the solenoid is de-energized, oil fl ows to the fi nal drives and the differential. When the solenoid is energized, oil fl ows to the differential only. The solenoid will be driven by the Brake ECM.


RAXL Pump Drive Oil Diverter Solenoid Feedback: The RAXL pump drive oil diverter solenoid feedback is used to read the status of the voltage being applied to the RAXL pump drive oil diverter solenoid. It is needed because the lube control solenoid is being operated from an Open Collector output driven by a relay. The brake ECM cannot directly read the status of the relay output without feedback. It will be read by the Brake ECM.

RAXL Final Drive Bypass Solenoid: The final drive bypass solenoid is used to divert pilot oil from the logic element which allows final drive oil back to the differential from the final drives. When the solenoid is de-energized, oil is directed to the pilot of the logic element blocking any lube oil flow to the differential and sending all oil to the final drives and the differential.

When the solenoid is energized, pilot oil to the logic element pilot is allowed to flow to the differential. The logic element moves to the lower envelope and the final drive oil flows back to the differential. The solenoid will be driven by the Brake ECM.

Rear Axle Lube Pump Drive Oil Diverter Solenoid: The RAXL lube pump drive oil diverter solenoid is used to divert steering pump supply oil flow away from the RAXL motor and return it to tank. When the solenoid is de-energized, steering pump supply oil flows to the RAXL motor. When the solenoid is energized, steering pump supply oil returns to tank. The solenoid will be driven by the Brake ECM.

��!6��"'��

��.- ��-> ��-? ��.,, ��

�#��., ��-- ��

0�"��-< ��.,> ��

1�"�4��&�9�'��

4��&�9��,-�$')��9�//�'��

4��&��,-�(')��@//�'��

��1��+��-�'��

�1

�1

��1��+��-�'��

��

��

��

��

�%!��!:%�*��2 !"2�1� "�!"%�3

��!6��

��

��#��

�1

-�'��1�.�'��

�1 ��

��1 �1

�1 �1

��.- ��-> ��-? ��.,, ��

0�"��-< ��.,> ��

�#��., ��-- ��

255

RAX Lubrication Strategy

This illustration shows the lubrication strategy for the rear axle. The main input that the Brake ECM uses to control the rear axle lube system is the temperature of the rear axle oil. This temperature, along with some basic information about the state of the machine, such as ground speed and engine speed, allows the Brake ECM to control the energizing of both the RAXL pump drive oil diverter solenoid and the RAXL fi nal drive bypass solenoid.

During start-up, the system is turned ON to charge the lube system. There is no advantage to lubing the rear axle due to the high viscosity of the cold oil. Therefore, the system is turned OFF after 5 minutes when the lube oil is cold. If the machine is traveling greater than 22 mph, the lube to the fi nal drives is cycled ON and OFF. This cycling prevents the fi lling of the fi nal drives due to centrifugal force by keeping only a small amount of oil in the fi nal drives.

The temperature gear limit is used to limit the actual transmission gear to keep the machine from doing any high speed traveling until the differential oil has warmed up enough for the lube system to be effective. When the temperature is below 13° C (55° F) the gear limit is 3rd gear. When the temperature is between 15° C (59° F) and 56° C (133° F), the gear will be limited to 4th gear.



Rear Axle Lube Pump Drive Oil Diverter Logic

When the engine is off, then the RAXL pump drive oil diverter solenoid is not energized. This strategy eliminates battery drain when the key switch is in the ON position without the engine running.

If the engine is running, or the running status is unknown, then the next set of conditions are checked.

1. If the machine is NOT MOVING and the diverter temperature status is either COOL or COLD and the diverter solenoid has been OFF for a minimum of 300 seconds, then the RAXL pump drive oil diverter solenoid can be turned energized. The five minute delay is intended to charge the system during typical machine start-up, and keep the RAXL pump drive oil diverter solenoid valve from cycling too often during typical machine operation.

2. If machine status is MOVING or MOVING FAST and the differential (oil) temperature status is COLD, then the RAXL manifold solenoid valve will be energized to divert oil flow. There is no advantage in lubing the rear axle due to the high viscosity of the rear axle lube oil under these cold conditions.

3. If the temperature status is HOT (Moving, Moving Fast or NOT Moving) or COOL with a MOVING or MOVING FAST machine status, then the RAXL pump drive oil diverter solenoid will be turned de-energized. This is the normal operating mode of the diverter. Oil will flow from the engine driven steering pump, which will in turn drive the RAXL motor, which will in turn drive the RAXL pump.


RAXL Control Valve

The new RAXL pump drive oil diverter valve (arrow) is located on the left inside of the truck frame above the rear axle. This valve controls the steering oil flow to the RAXL motor when the conditions are met

The lower illustration shows the components of the RAXL pump drive oil diverter valve and the flow paths into and out of the valve. The hose (1) supplies steering pump supply oil through the steering valve (not shown) at the front of the truck

257

256

7

23

4

5

1

6


The pump drive oil diverter valve is equipped with a solenoid valve (2). The solenoid valve is normally de-energized when the key start switch is in the OFF position and/or the differential oil temperature is above 13° C (55° F).

The diverter valve is also equipped with a sequence valve (3). This valve blocks oil flow from hose (5) when the steering oil pressure is below 13800 kPa (2000 psi). In the flow path between the solenoid valve and the sequence valve within the valve is the variable flow control (3). While oil is flowing past the sequence valve, the flow control valve is limiting flow to approximately 7.5 L/min (118 Gal/hr).

The hose (5) supplies a path of oil between the RAXL pump drive oil diverter valve and the RAXL motor. The hose (5) supplies a path to tank from both the RAXL motor. The combination of the RAXL motor drain and the drain from the diverter flows back to the hydraulic tank (not shown) through hose (7).

The following Diagnostic Code covers the RAXL solenoid control valve. MID 116 - Brake ECM

- CID 1437 - FMI 03 - Solenoid (Rear Axle Supply) Voltage above normal - CID 1427 - FMI 06 - Solenoid (Rear Axle Supply) Current above normal


259

258

RAXL Pump Drive Oil Diverter Solenoid Relay Control

The upper illustration shows the location of the solenoid relay control (arrow). To access the relay control, remove the rear cover from the cab.

The lower illustration shows the relay control (1) and the plug (2). This relay controls the RAXL pump drive oil diverter solenoid (located on the frame) and the final drive bypass solenoid (on the diverter valve on the axle).

��$�% 4

A. A/

A.�/?

A.�,- A/�B9

A/�/<

A/�>A.�,/

A/�.9

C��

��#��

�!:��'��#��#��

#�++��

#�++��

#�++��"'��

��#�� $

�!:��'��#��#�� $

�%!��!:%�*��2 !"2�1�%% "�2 !� 3 "%4

�!:��'��#��#��

��

260

The illustration above shows the electrical diagram for the rear axle lubrication system.


Differential Lube

When the control temperature reaches the appropriate value for the 785D truck, the RAXL pump drive oil diverter valve directs steering oil to the RAXL drive motor (not shown). The motor drives the pump and oil from the differential sump is drawn through the tube and strainer (1), through the hose (2) to the pump. From the pump, oil is directed to the RAXL diverter valve (3) through the hose (4) (lower illustration). The oil is directed through the hose (5) to the hose (6) which is internal located between the transmission and the differential. Also, oil is ported through the differential case to the three tubes which are located on the reverse side compared to the hose (5). These three tubes (upper illustration) lubricate the pinion gear and the bearings on each side of the carrier.

261

262


1

2

4

3

5

6

7

RAXL Final Drive Bypass Valve

The RAXL final drive bypass valve is located on the rear of the banjo on the left side. This valve has two purposes, one is that is diverters the oil from the banjo housing for filtration. Also, the valve is used to divide the oil flow between the differential and the final drives.

The differential lube oil filter is equipped with an internal bypass valve (5) allowing the oil to flow into the filtered oil of the filter. On the filter base, there is a S•O•S port (6). This port is used to check the quality of the oil lubricating moveable components in the axle. Also, the diverter valve has a relief valve (4) for limiting the pressure through the RAXL filtration system preventing over-pressurization.

263

264


2

34

5

8

7

6

1


Between the path of oil to the differential lube and the final drive lube is an orifice (not shown). The orifice restricts the flow of oil to the final drives. The diverter valve has two position solenoid valve (2) which controls the pilot oil pressure to the pilot end of the diverter valve (1). In the relaxed position, the solenoid valve sends flow to the pilot end of the diverter, holding the diverter in the blocked position.

The following Diagnostic Code covers the RAXL final drive bypass solenoid valve. MID 116 - Brake ECM

- CID 1232 - FMI 03 - Solenoid (Rear Axle Diverter) Voltage above normal - CID 1232 - FMI 06 - Solenoid (Rear Axle Diverter) Current above normal

Installed on the diverter valve is a pressure tap (3). This pressure tap measures the pressure of the final drives lubrication.

The lower illustration shows the location of the ports on the lower side of the diverter valve. The port (7) directs lubrication oil to the final drives.

The port (8) directs oil to the differential housing.

RAXL Motor and Pump

The RAXL pump (2) is a single section gear pump.

The RAXL motor (1) is also a single section gear motor which rotates in the counterclockwise direction when looking at the gear motor from the drive shaft end.

265

1

2


Temperature and Pressure Sensors for the RAXL

The upper illustration shows the location of the differential housing oil temperature sensor (1). The Brake ECM uses this sensor to determine whether the solenoid valve on the RAXL control valve will be de-energized.

The following Diagnostic Code covers this temperature sensor. MID 116 - Brake ECM- CID 0835 - FMI 03 - Temperature sensor (Differential Oil) Voltage above normal - CID 0835 - FMI 04 - Temperature sensor (Differential Oil) Voltage below normal

The right side level sensor is not shown.

267

266

1 2

3 4


The housing is equipped with two level sensors one for each side of the axle. Level sensor (2) is shown in the illustration, monitors the oil level in the left side of the differential housing.

The lower illustration shows the differential lube oil filter base with the differential lube oil pressure sensor and the differential oil filter pressure switch installed. The pressure sensor monitors the pressure of oil from the filter into the diverter valve. This sensor is also used for gear shift limiting with a low RAXL pressure situation.

The differential oil filter pressure switch monitors the difference in pressure at the filter inlet and outlet.


#


CONCLUSION

This presentation has provided a basic introduction to the Caterpillar 785C 785D, and 789C Off-highway Trucks. All the major component locations were identified and the major systems were discussed. When used in conjunction with the service manual, the information in this package should permit the serviceman to analyze problems in any of the major systems on these trucks.

268

HYDRAULIC SCHEMATIC COLOR CODE

This illustration identifies the meanings of the colors used in the hydraulic schematics and cross-sectional views shown throughout this presentation.

SERV1857 - 326 - 06/08

Red - High Pressure Oil

Red / White Stripes - 1st Pressure Reduction

Pink - 3rd Reduction in Pressure

Red / Pink Stripes - Secondary Source Oil Pressure

Orange - Pilot, Charge or Torque Converter Oil

Blue - Trapped Oil

Brown - Lubricating Oil

Cat Yellow - (Restricted Usage)

Green / White Stripes -Scavenge / Suction Oil or Hydraulic Void

Identification of Componentswithin a Moving Group

Black - Mechanical Connection. Seal

Dark Gray - Cutaway Section

Light Gray - Surface Color

White - Atmosphere or Air (No Pressure)

Purple - Pneumatic Pressure

Yellow - Moving or Activated Components

Orange / Crosshatch - 2nd Reduction in Pilot,Charge, or TC Oil Pressure

Orange / White Stripes - Reduced Pilot, Charge, orTC Oil Pressure

Red Crosshatch - 2nd Reduction in Pressure

Green - Tank, Sump, or Return Oil

HYDRAULIC SCHEMATIC COLOR CODE

Red

- H

igh

Pres

sure

Oil

Red

/ W

hite

Str

ipes

- 1

st P

ress

ure

Red

uctio

n

Pink

- 3r

d R

educ

tion

in P

ress

ure

Red

/ Pi

nk S

trip

es -

Seco

ndar

y So

urce

Oil

Pres

sure

Ora

nge

- Pilo

t, C

harg

e or

Tor

que

Con

vert

er O

il

Blu

e - T

rapp

ed O

il

Bro

wn

- Lub

ricat

ing

Oil

Cat

Yel

low

- (R

estr

icte

d U

sage

)

Gre

en /

Whi

te S

trip

es -

Scav

enge

/ Su

ctio

n O

il or

Hyd

raul

ic V

oid

Iden

tific

atio

n of

Com

pone

nts

with

in a

Mov

ing

Gro

up

Bla

ck -

Mec

hani

cal C

onne

ctio

n. S

eal

Dar

k G

ray

- Cut

away

Sec

tion

Ligh

t Gra

y -

Surf

ace

Col

or

Whi

te -

Atm

osph

ere

or A

ir (N

o Pr

essu

re)

Purp

le -

Pneu

mat

ic P

ress

ure

Yello

w -

Mov

ing

or A

ctiv

ated

Com

pone

nts

Ora

nge

/ Cro

ssha

tch

- 2nd

Red

uctio

n in

Pilo

t,C

harg

e, o

r TC

Oil

Pres

sure

Ora

nge

/ Whi

te S

trip

es -

Red

uced

Pilo

t, C

harg

e, o

rTC

Oil

Pres

sure

Red

Cro

ssha

tch

- 2nd

Red

uctio

n in

Pre

ssur

e

Gre

en -

Tank

, Sum

p, o

r Ret

urn

Oil

HYD

RA

ULI

C S

CH

EMAT

IC C

OLO

R C

OD

E

SERV1857 - 327 - Serviceman's Handout06/08

1.

VISUAL LIST

1. 789C model view 2. Right side 789C truck 3. Front of 789C truck 4. Truck body options 5. Walk around inspection 6. Maintenance checks 7. Front wheel bearing 8. Front suspension cylinder 9. Air filter housing 10. Right side engine 11. Transmission charging filter 12. Transmission hydraulic tank 13. Final drive 14. Differential oil level 15. Safety cable 16. Fuel tank 17. Primary fuel filter 18. Parking brake and torque converter 19. Brake cylinder breathers 20. Front air dryer 21. 789C engine oil filters 22. 785C engine oil filters 23. Oil change connector 24. Secondary fuel filters 25. Engine shutdown switch 26. Air filter restriction indicators 27. 789C cooling system 28. Air cleaner indicators 29. Ether cylinders 30. Batteries 31. Lubrication tank 32. Steering system tank 33. Air tank drain valve 34. Windshield washer reservoir 35. Daily checks 36. Operator's station 37. Operator and trainer seats 38. Hoist control lever 39. Dash (left side) 40. Operator controls 41. Switches and signals 42. Manual retarder lever

43. Brake and throttle pedals 44. Shift console 45. Overhead switches 46. Circuit breaker panel 47. Center dash panel 48. Rocker switches 49. VIMS message center module 50. VIMS interface modules 51. VIMS main module 52. VIMS diagnostic connector 53. Electronic Technician (ET) 54. 3516B engine model view 55. Electronic control system component

diagram 56 Engine ECM 57. Atmospheric pressure sensor 58. Engine speed/timing sensor 59. Throttle position sensor 60. EUI fuel injector solenoid 61. Input switches and sensors 62. Air conditioner compressor switch 63. Crankcase pressure sensor 64. ECM logged events 65. Additional ECM logged events 66. Systems controlled by ECM 67. Engine oil pre-lubrication 68. Speed fan control 69. Oil renewal system components 70. Oil level switches 71. Cooling system 72. Radiator 73. Water pump 74. Coolant 75. Engine (right side) 76. Jacket water coolant flow 77. Auxiliary (aftercooler) water pump 78 Rear aftercooler temperature sensor 79. 789C air charging system 80. Lubrication system 81. Oil filters 82. 785C engine oil filters 83. Engine oil system

VISUAL LIST

SERV1857 - 328 - 06/08

1.

VISUAL LIST

SERV1857 - 329 - 06/08

84. Primary fuel filter 85. Fuel transfer pump 86. Secondary fuel filters 87. Fuel injectors 88. Fuel system circuit 89. Air induction and exhaust system 90. Turbocharger inlet pressure sensor 91. 351B turbochargers 92. Exhaust temperature sensor 93. 3512B air induction and exhaust system 94. Power train components 95. Torque converter 96. Torque converter (converter drive) 97. Torque converter drive (direct drive) 98. Torque converter pump (four sections) 99. Torque converter charging filter 100. Torque converter inlet relief valve 101. Torque converter outlet screen 102. Brake oil cooler and diverter valve 103. Parking brake release valve 104. Torque converter lockup clutch valve

(iron) 105. Torque converter lockup clutch control

(direct drive) 106. Torque converter hydraulic system 107. Transfer gears 108. Transmission lube supply hose 109. Power shift planetary transmission 110. Transmission pump 111. Transmission scavenge screens 112. Transmission charging filter 113. Transmission oil cooler bypass valve and

oil cooler 114. Transmission charging pump 115. Transmission clutch pressures 116. ICM transmission controls (sectional

view) 117. Transmission hydraulic system 118. Rear axle pump 119. Pump supply hose 120. Oil filter bypass switch

121. Rear axle oil cooling and filter system 122. Double reduction planetary gear final

drives 123. Transmission/Chassis ECM 124. Transmission/Chassis electronic control

system 125. Shift lever switch 126. Transmission gear switch 127. Transmission Output Speed (TOS)

sensor 128. Service/retarder brake switch 129. Body position sensor 130. Steering system 131. 789C steering system (no steer/

maximum flow 132 785C steering system (hold) 133. Steering tank and filter 134. 785C steering pump 135. 785C steering pump (maximum flow) 136. Pump compensator valve 137. 785C steering pump (minimum flow) 138. 789C steering pump 139. 789C steering pump supply oil 140. 789C steering pump operation

(maximum flow) 141. 789C steering pump (low pressure

standby) 142. Accumulator charging valve 143. Load sensing controller 144. 789C solenoid and relief valve manifold 145. 785C solenoid and relief valve manifold 146. Solenoid and relief valve manifold

(sectional view) 147. 789C steering directional valve 148. Steering directional valve (no turn) 149. Steering directional valve (right turn) 150. 785C solenoid and relief valve manifold

and crossover relief valves 151. 785C crossover relief system (external

impact) 152. 789C Hand Metering Unit (HMU) 153. 789C steering accumulators

VISUAL LIST

1.

VISUAL LIST

154. Shutdown control 155. Hoist control system 156. Hoist lever 157. Hoist control position sensor 158. Hoist, converter and brake tank 159. Hydraulic tanks (rear) 160. Two-section hoist pump 161. Hoist screens 162. Pump supply ports 163. Counterbalance valve 164. Hoist control valve (hold) 165. Hoist control valve (raise) 166. Hoist counterbalance valve (raise, lower

and float) 167. "C" Series hoist control valve (lower) 168. "C" Series hoist control valve (float) 169. Two-stage hoist cylinders 170. Hoist system (hold) 171. Air and brake systems 172. Oil cooled brake assembly (cutaway) 173. Air charging system 174. 789C air dryers 175. Service/retarder brake tank 176. Pressure protection valve 177. Automatic lubrication solenoid air valve 178. Parking/secondary brake tank 179. 789C air charging system 180. Manual retarder valve 181. Service brake valve 182. Inverter valve signal port 183. Brake release valve 184. Normal parking and secondary brake

operation 185. Parking/secondary brakes released and

parking brakes engaged 186. Service brake and manual retarder relay

valve 187. Brake oil makeup tank 188. Brake cylinder (engaged) 189. Slack adjuster (iron) 190. Slack adjuster (released and engaged)

191. Service/retarder brake air system (engaged)

192. 789C brake oil cooling schematic 193. Brake cooling oil pressure tap 194. Brake electronic control system 195. Brake ECM (iron) 196. Automatic Retarder Control (ARC)

schematic 197. Engine Output Speed (EOS) sensor 198. Retarder pressure switch 199. Service/retarder brake air system 200. Hydraulic ARC System 201. Hydraulic ARC Valve 202. Engine On/ARC Off 203. Engine On/ARC On 204. Engine Off/ARC Off 205. Automatic retarder control schematic

(engaged) 206. Steering bleed down control 207. Brake cooling diverter solenoid 208. Engine Output Speed (EOS) sensor 209. Traction Control System (TCS)

schematic 210. Wheel speed sensor 211. Traction Control System (TCS) valve 212. Traction Control System (TCS)

operation (brakes released) 213. Traction Control System (TCS)

operation (left brake engaged) 214. Flexxaire™ fan 215. Flexxaire™ fan electronic control box 216. 785D large off-highway truck 217. 3512C high displacement engine 218. Engine components (right side) 219. Engine components (left side) 220. Engine components (front) 221. Engine components (rear) 222. Turbocharger location 223. Engine Electronic Control Module

diagram 224. Engine ECM and atmospheric pressure

sensor 225. Injector with valve cover removed 226. Primary speed/timing sensor 227. Engine speed sensor

VISUAL LIST

SERV1857 - 330 - 06/08

VISUAL LIST

228. Coolant temperature sensor 229. Coolant flow switch 230. Crankcase pressure sensor 231. Turbo inlet pressure sensors (left) 232. Turbo inlet pressure sensors (right) 233. Intake manifold air temperature sensor 234. Intake manifold pressure sensor (boost) 235. Exhaust temperature sensor (left side) 236. Exhaust temperature sensor (right side) 237. Fuel filter differential switch 238. Rear oil pressure sensor 239. Front oil pressure sensor 240. 3512C logged events 241. Systems controlled by ECM 242. Fuel system diagram 243. Fuel priming pump 244. Fuel priming pump toggle switch 245. Fuel pressure regulator 246. Fuel system diagram (fuel priming) 247. Timing bolt and access cover 248. Steering and front brake oil cooling

system 249. Steering and front brake oil cooling

system 250. Air induction and exhaust system "D"

series truck

SERV1857 - 331 - 06/08

251. Air flow to inlet of ATAAC 252. Air flow from the ATAAC 253. 785D rear axle lubrication (RAXL) 254. "D" series RAXL filtration (warm oil) 255. RAX lubrication strategy 256. RAXL pump drive oil diverter valve 257. RAXL pump drive oil diverter valve

(components) 258. Solenoid relay control connector 259. Solenoid relay control and connector 260. Electrical diagram for the rear axle

lubrication system 261. Differential lube - tube and strainer 262. Differentail lube - (hoses) 263. RAXL final drive bypass valve 264. Diverter valve ports 265. RAXL motor and pump 266. Differential housing oil temperature

sensor 267. Differential lube oil filter base 268. Truck rear view

VIMS KEYPAD OPERATIONSThe keypad allows the operator or a service technician to interact with the VIMS. Some of the functions that can be performed by the keypad are:

PAYCONF 7292663 Configure Payload Monitor (requires VIMS PC connection)PAYCAL 729225 Calibrate Payload Monitor (requires VIMS PC connection)TOT 868 Show Payload Cycle Resettable TotalsRESET 73738 Reset Displayed Payload DataESET 3738 Customize Events (requires VIMS PC connection)SVCLIT 782548 Turn OFF Service LightSVCSET 782738 Service Light Set (requires VIMS PC connection)TEST 8378 Self Test InstrumentationMSTAT 67828 Show Machine Statistics (source and configuration codes)LUBSET 582738 Set Lube Cycle TimesLUBMAN 582626 Manual LubeEACK 3225 Show Acknowledged Events (Active)ESTAT 37828 Show Event StatisticsELIST 35478 Show Event List (Intermittent)EREC 3732 Start Event RecorderERSET 37738 Configure 1 Event Recorder (requires VIMS PC connection)DLOG 3564 Start/Stop Data LoggerDLRES 35737 Reset Data LoggerLA 52 Change LanguageUN 86 Change UnitsODO 636 Odometer Set/Reset (requires VIMS PC connection)BLT 258 Change BacklightCON 266 Change Display ContrastATTACH 288224 Used to recognize if RAC module is present (0 - NO, 4 - YES)RAC 722 Set Haul Road Severity (0 - OFF, 1 - high, 2 - medium, 3 - low) (requires VIMS PC connection)

OK Key: Used to complete keypad entries and to acknowledge events. Acknowledging an event will remove the event from the display temporarily. Severe events cannot be acknowledged.GAUGE Key: Displays parameters monitored by the VIMS. Depressing the arrow keys will scroll through the parameters. Entering the parameter number and the GAUGE key selects that parameter.F1 Key: Provides additional information on the current event being displayed. For MAINTENANCE events, the MID, CID, and FMI are displayed. For DATA events, the current parameter value is displayed (temperature, pressure, rpm).


serv1857 785c (1hw), 785d (msy), 789c 2bs)_txt[1].pdf

Documents

highway truck aehq5320789c

highway truck aehq5321793c

air system

traction control system

basic maintenance information

power train

c hd engine

service personnel