oht - 785c and 789c - serv1706 - student handout - oct 05

SERV1706-01July 2005

TECHNICAL PRESENTATION

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

Service Training Meeting Guide(STMG 706)

SERVICE TRAINING

785C (1HW),789C (2BW) OFF-HIGHWAYTRUCKSMEETING GUIDE 706 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 operationof 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 andthe 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 systems.

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 HoursVisuals: 216 VisualsServiceman Handouts: 16 Data SheetsForm: SERV1706-01

© 2005 Caterpillar Inc. Date: 7/05

SERV1706-01 - 3 - Text Reference7/05

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 CONTENTS

INTRODUCTION ........................................................................................................................7

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

OPERATOR'S STATION............................................................................................................42

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........................................................................................124Transmission 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

CONCLUSION.........................................................................................................................266

VISUAL LIST ..........................................................................................................................267

SERVICEMAN'S HANDOUTS...............................................................................................270

NOTES


INTRODUCTION

Shown is the 789C Off-highway Truck. The "C" Series trucks are the same as the "B" Seriesexcept for the following changes: 3500B engines, improved cab, two different ElectronicControl Modules (Transmission/Chassis and Brake) and an electronically controlled hoist. The789C 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 beenreplaced with the Transmission/Chassis Electronic Control System. The Transmission/ChassisElectronic Control Module (ECM) controls the same functions as the EPTC II plus the hoist andsome other functions.

The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control moduleshave been replaced with one Brake System ECM. The Brake System ECM controls both theARC and the TCS functions. The TCS is now connected to the CAT Data Link and theElectronic 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 trucksare: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

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785C (1HW), 789C (2BW) OFF HIGHWAY TRUCKS

© 2005 Caterpillar Inc.


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Shown is the right side of a 789C truck. The large air tank on the right platform supplies air forstarting 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 otherhydraulic systems.

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

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

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The truck bodies on "C" Series trucks are mandatory options. Two body styles are available forthe "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. Allattachment body liners are also made with 400 Brinell hardness steel. The external componentsof 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 steelplate. The rear one-third of the body floor is made with a 10 mm (.39 in.) thick 400 Brinell subplate and a 20 mm (.79 in.) thick 400 Brinell body grid liner plate. As an option, the grid linerplate can be made with 500 Brinell steel.

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

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WALK AROUND INSPECTION

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

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

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

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


785C/789C MAINTENANCE

789C Service

Procedure

WALK AROUND INSPECTION

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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 framestructures

- 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


Steering Oil Level

Batteries

Coolant Level

Wheel Nuts

Engine Oil Level

Air Filter,Restriction Indicators

and Precleaners

Fuel Level andDrain Moisture

TransmissionOil Level Hoist, Converter

and Brake Oil Level

Belts and Ether Cylinders

Tire InflationPressure

Suspension Cylinder Height

Suspension Cylinder Height,Grease Breathers

and Wheel Breathers

Rear Axle andBrake Cylinder

Breathers

Frame For Cracks andBody Support Pads

Leaks and Trash Build-upAir Reservoir Moisture

Windshield Washer Leveland A/C Filter

Auto Lube Reservoir

Rear Axle Oil Level

Wash Windows,Cab Fresh Air Filters,

Seat Belt, Indicators, Gauges,Brake Tests

Secondary Steering andBack-up Alarm

10 HOURS/DAILY MAINTENANCE CHECKS

The front wheel bearing oil level is checked and filled by removing the plug (1) in the center ofthe wheel bearing cover. The oil should be level with the bottom of the plug hole. The fill plugis a magnetic plug. Inspect the fill plug weekly for metal particles. If any metal particles arefound, remove the wheel cover and inspect the bearings for wear. The oil is drained byremoving 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 aspecification of (TO-4) or newer. FDAO and TDTO TO-4 provides increased lubricationcapability for bearings.

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

NOTE: Care must be taken to ensure that fluids are contained while performing anyinspection, maintenance, testing, adjusting and repair of the machine. Be prepared tocollect the fluid in suitable containers before opening any compartment or disassemblingany component containing fluids. Refer to the "Tools and Shop Products Guide" (FormNENG2500) for tools and supplies suitable to collect and contain fluids in Caterpillarmachines. Dispose of fluids according to local regulations and mandates.

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

Inspect the condition of the front wheel bearing axle housing breather (1). The breather preventspressure from building up in the axle housing. Pressure in the axle housing may cause brakecooling 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 greasesupply line for the Auto Lubrication System is located at the rear of the suspension cylinder. Nogrease outlet fittings should be located on the same side of the suspension cylinder as the greasefill location. An outlet fitting positioned on the same side of the suspension cylinder as thegrease fill location will prevent proper lubrication of the cylinder.

Make sure that grease is flowing from the outlet fittings to verify that the suspension cylindersare 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).

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

The dust valve is OPEN when the engine is OFF and closes when the engine is running. Thedust valve must be flexible and close when the engine is running or the precleaner will notfunction properly and the service life of the air filters will be reduced. Replace the rubber dustvalve if it becomes hard and brittle.

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

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

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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 inthe tube between the engine oil cooler and the engine oil filters.

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

An oil filter bypass switch is located on each filter. The transmission oil filter bypass switchesprovide input signals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sendsthe signals to the VIMS, which informs the operator if the filters are restricted. The torqueconverter 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 eachcycle.

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

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

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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 enginestopped. 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 thetank when the hoist cylinders are in the RAISED position. When the hoist cylinders arelowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check thehydraulic tank oil level with the upper sight gauge.

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

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

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

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

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.

NOTICE

Failure to correctly fill the hydraulic tanks after an oil change may cause componentdamage.


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 oillevel is checked and filled by removing the magnetic plug (arrow). The oil should be level withthe bottom of the plug hole. Fill the rear axle housing with oil before filling the final drives withoil. Allow enough time for the oil to settle in all of the compartments. This can be as much as20 minutes during cold temperatures.

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

Use only Final Drive and Axle Oil (FDAO) or Transmission Drive Train Oil (TDTO) with aspecification 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 driveor the differential fails, the other final drive components must also be checked forcontamination and then flushed. Failure to completely flush the rear axle after a failurecan cause a repeat failure within a short time.

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

Two oil level sensors (2) provide input signals to the Brake ECM. The Brake ECM sends thesignals 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 conditionof the rear suspension cylinders when the truck is empty and on level ground. Measure thecharge height of the suspension cylinders and compare the dimension with the dimension thatwas recorded the last time the cylinders were charged. Recharge the cylinders with oil andnitrogen if necessary.

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

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

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5

The cable that holds the body up is stored below the rear of the body. Whenever work is to beperformed while the body is raised, the safety cable must be connected between the body and therear 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 islowered. Failure to install the cable can result in injury or death to personnel working inthis area.

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WARNING

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

The percentage of sulfur in the fuel will affect the engine oil recommendations. The following isa 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.

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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 ultrasonicsignal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonicsignal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signalchanges 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) isshown 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 than10%.

The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of thesensor, 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 withthe fuel level. To check the output signal of the fuel level sensor, connect a multimeter betweenPins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The dutycycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depthand 84% at 2000 mm (78.8 in.) of fuel depth.

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

An oil filter bypass switch is located on each housing. The parking brake filter bypass switchprovides an input signal to the Brake ECM and the torque converter outlet screen bypass switchprovides an input signal to the VIMS. The Brake ECM sends the signal to the VIMS, whichinforms 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.

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Inspect the condition of the three breathers (1) (two visible) for the brake cylinders. The thirdbreather is located on the front brake master cylinder behind the cross tube. Oil should not leakfrom the breathers. Oil leaking from the breathers is an indication that the oil piston seals in thebrake cylinder need replacement. Air flow from the breathers during a brake applicationindicates 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 thecylinder will overstroke and cause an indicator rod to extend and open the brake overstrokeswitch (2). The switch provides an input signal to the VIMS, which informs the operator of thecondition of the service and retarder brake oil circuit. If an overstroke condition occurs, theproblem must be repaired and the indicator rod pushed in to end the warning.

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On the 789C truck, the second air dryer (1) is located in front of the left front suspensioncylinder. 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-4specification 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 narrowerperformance band.

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

- Has better fuel sulfur neutralization capability.

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The engine oil filters (789C shown) are located on the left side of the engine. Engine oil shouldbe added at the fill tube (1) and checked with the dipstick (2). The 785C has three engine oilfilters 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 locatedon 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 theEngine 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 theoperator 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, andhas a narrower performance band.

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

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

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

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

NOTICE

When changing the engine oil filters, drain the engine oil that is trapped above the oilfilters through the fitting (1) to prevent spilling the oil. Oil added to the engine through thefitting 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 systemand cause damage to the engine.

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

An engine oil level switch (2) provides input signals to the Engine ECM. The Engine ECMprovides 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 operatethe truck without causing damage to the engine. The ENG OIL LEVEL LOW message is aCategory 2 or 3 Warning.

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

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

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

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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 beused to stop the engine from the ground level. Operate the switch periodically to check thesecondary steering system.

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

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

The battery disconnect switch (4) and VIMS service connector key switch (5) must be in the ONposition 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 ONposition, the VIMS runs through a self test. During the self test, the service lamp will flash threetimes if any logged events are stored in the VIMS main module and once if no logged events arestored.

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

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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 thefilters are plugged), the air filters must be serviced. Check the dust valves (2) for plugging. Ifnecessary, disconnect the clamp and open the cover for additional cleaning. Replace the dustvalve if the rubber is not flexible.

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

Two filter elements are installed in the filter housings. The large element is the primary elementand 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).

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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) hasbeen added above the radiator.

The cooling system on the "C" Series trucks is divided into two systems. The two systems arethe jacket water cooling system and the aftercooler cooling system. These two systems are notconnected. When servicing the cooling systems, be sure to drain and fill both systemsseparately.

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

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

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

27


1 2

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

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 theyellow pistons are in the red zone (indicating that the filters are plugged), the air cleaners mustbe serviced.

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

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11

2

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

The Engine ECM will automatically inject ether from the ether cylinders during cranking. Theduration of automatic ether injection depends on the jacket water coolant temperature. Theduration 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 enginespeed 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 batteryconnections for corrosion or damage. Keep the battery terminals clean and coated withpetroleum jelly.

Inspect the electrolyte level in each battery cell, except for maintenance free batteries. Maintainthe 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 cancause 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


WARNING

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

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

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

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1

23

The oil level for the steering system tank is checked at the upper sight gauge (1) when the oil iscold and the engine is stopped. After the engine is started, the oil level will decrease as the oilfills 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 levelshould not be below the ENGINE RUNNING marking of the lower gauge. If the ENGINERUNNING level is not correct, check the nitrogen charge in each accumulator. A low nitrogencharge will allow excess oil to be stored in the accumulators and will reduce the secondarysteering capacity.

Before removing the cap to add oil to the steering system, be sure that the engine was shut offwith 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 pressurefrom 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 attachan Auxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at theconnector (6) to charge the steering accumulators. Steering capability is then available to towthe truck.

32


1

2

3 4

5

6

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


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

33


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

The air conditioner filter (2) is also located in the compartment in front of the cab. Clean orreplace 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 inFIRST FORWARD. Accelerate the engine until the truck moves. The truck must not movebelow 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 airfilter when necessary.

INSTRUCTOR NOTE: Refer to the Operation and Maintenance Manual for moreinformation 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 improveoperator comfort and ergonomics. The "C" Series cab now resembles the cab used on thesmaller "D" Series Off-highway Trucks.

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

During loading, the green (continue loading) lamps will be ON until the payload is 95% of thetarget weight setting. Then, the red (stop loading) lamp will light. A "last pass" indication canbe programmed into the system using the VIMS Keypad. With last pass indication, the VIMScalculates an average loader pass size and predicts payload weight. If the predicted weight afterthe 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 functioncorrectly.

36


Shown is a view of the operator's seat and the trainer's seat. The seats are more comfortablewith 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 havecontrol over the SNUB position. The body position sensor (see Visual No. 129) controls theSNUB position of the hoist valve. When the body is lowered, just before the body contacts theframe, the Transmission/Chassis ECM signals the hoist solenoids to move the hoist valve spoolto the SNUB position. In the SNUB position, the body float speed is reduced to prevent hardcontact of the body with the frame.

The truck should normally be operated with the hoist lever in the FLOAT position. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andbody 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 usedto 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, thelever 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 improvementsare:

- 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 portis 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 poweredwindshield 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 awayfrom 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 manualretarder lever is used to modulate engagement of the service brakes on all four wheels. Theretarder system allows the machine to maintain a constant speed on long downgrades. Theretarder 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

NOTICE

Do 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 fourwheels.

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

- Throttle pedal (3): A throttle position sensor is attached to the throttle pedal. The throttleposition 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 earliertrucks must be programmed to a 10 to 50% throttle position. The setting is changed inthe Engine ECM configuration screen with ET.

The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolanttemperature 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 atLOW IDLE (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion and overcooling. Totemporarily reduce the elevated idle speed, the operator can release the parking brake or depressthe 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 thetransmission 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/ChassisECM. The top gear limit can be changed from THIRD to SIXTH. The body up gear limit canbe 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" Seriestrucks used fuses to protect many of the electrical circuits. The "C" Series trucks use onlycircuit 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 laptopcomputer.

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

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

46


1

2

3

Shown is the center of the front dash panel. Eight dash indicators, the four-gauge clustermodule, 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 tobottom):

- 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 whena 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 bedisplayed 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 twodigits that show the actual transmission gear that is engaged. The left digit shows theactual 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 rockerswitches 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 oiltemperature is below 10°C (50°F) and engine speed is below 1900 rpm. The manual etherinjection 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 hoistpilot oil to lower the body with a dead engine. The small latch must be pushed UP beforethe switch can be pushed DOWN.

- TCS test: Tests the Traction Control System (TCS). Use this switch when turning in atight circle with the engine at LOW IDLE and the transmission in FIRST GEAR. Thebrakes should ENGAGE and RELEASE repeatedly. The test must be performed whileturning 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 thekeypad module (2).

The message center module consists of an alert indicator, a universal gauge, and a messagedisplay 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 forviewing by depressing the GAUGE key on the keypad.

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

49


1

2

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

Warning Category 1

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

Warning Category 2

For a Category 2 Warning, the alert indicator and the action lamp will flash. The universalgauge may display the parameter and a message will appear in the message display window. ACategory 2 warning alerts the operator that a change in machine operation is required to avoidpossible damage to the indicated system. The "OK" key on the keypad can be used toacknowledge the warning. Some warnings will be silenced for a predetermined period. Afterthis 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 continuousaction alarm will sound, which indicate a SEVERE Category 2 Warning. The universal gaugemay display the parameter and a message will appear in the message display window. ACategory 2-S Warning alerts the operator to immediately change the operation of the machineto avoid possible damage to the indicated system. When the change in operation is made to anacceptable 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 alarmwill sound intermittently. The universal gauge may display the parameter and a message willappear in the message display window. A Category 3 Warning alerts the operator that themachine must be safely shut down immediately to avoid damage to the machine or preventpersonal 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 sensorslocated around the machine. The VIMS also communicates with other electronic controls on themachine. The VIMS provides the operator and the service technician with a complete look atthe 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 tothe TPMS information is provided through the VIMS message center and keypad modules and alaptop computer with the VIMS PC software installed.

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


Transmission /Chassis ECM

EngineECM

ServiceLamp

MessageCenterModule

GaugeClusterModule

KeypadModule

Sensors

Vims InterfaceModule

Vims InterfaceModule

Sensors

VIMSService Tool

andSoftware

CAT Data Link

ServiceKey Start

Switch

ActionLamp

ActionAlarm

ElectronicTechnician /ECAP

Vims Main Module

Display Data Link

VIMSRS-232

Port

CAT Data Link

VITAL INFORMATIONMANAGEMENT SYSTEM

(VIMS)

Speedometer/Tachometer

Module

KeypadData Link

Brake ECM(ARC /TCS)

3F1 2 MPHkm/h

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 ControlSystem (TCS), and rear axle cooling.

The Transmission/Chassis ECM controls the shifting of the transmission, torque converterlockup, 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 theCAT Data Link. All the information from these controls can be accessed through the VIMSmessage 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 laptopcomputer is connected to the VIMS diagnostic connector.

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

- 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 ServiceManual Modules "Off-Highway Truck/Tractors Vital Information Management System(VIMS)--System Operation" (Form RENR2630) and "Off-Highway Truck/Tractors VitalInformation Management System (VIMS)--Testing and Adjusting Troubleshooting" (FormRENR2631).

52


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

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

53


ENGINE

Shown is the 3516B engine used in the 789C Off-highway Truck. The 789C is equipped withthe Caterpillar 3516B quad turbocharged and aftercooled engine. The 785C is equipped with theCaterpillar 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 andeconomy 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. TheEngine ECM analyzes these signals and determines when and for how long to energize theinjector solenoids.

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


A/C PressureSwitch

CrankcasePressure

Ground LevelShutdown Switch

Fuel FilterSwitch

Pre-lubrication Relay

Oil LevelSwitch (Low)

Fan Fan Speed Sensor

Fan ClutchSolenoid

Service Tool

CAT Data Link

Engine Coolant Temperature

EngineECM

GroundBolt

15 AmpBreaker

MainPower Relay

Key StartSwitch

Speed /Timing Sensor

Engine Oil Pressure(Unfiltered)

Coolant Flow Switch

Timing ProbeConnector

Ether Solenoid

Disconnect Switch

3500B ELECTRONIC CONTROL SYSTEMCOMPONENT DIAGRAM

Electronic UnitInjectors

Turbo Outlet Pressure (Boost)

Right Turbo Inlet Pressure

Atmospheric Pressure

Engine Oil Pressure (Filtered)

Throttle

Engine OilRenewal Solenoid

Shutter Solenoid

Rear Aftercooler Temperature

Left Turbo Inlet Pressure

Right Turbo Exhaust

Left Turbo Exhaust

Throttle Override Switch

Manual EtherSwitch


Brake ECMVims

24 V

"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 areused on most sensor and switch inputs of electronic controls. Frequency sensors do not receivea pull-up voltage (except for suspension cylinder pressure sensors). The pull-up voltage isdetermined by the ECM design and will vary between ECMs. Pull-up voltage sometimes is thesame 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 mostoften HAS NO relationship to the voltage that POWERS the sensor. PWM sensors most oftenhave 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 voltagethat powers them. The Engine ECM will provide a "pull-up voltage" to the signal circuit of thesensors when the ECM senses an OPEN circuit. The signal circuit is pin C of the 3-pin sensorconnectors. 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 followingprocedure (key start switch must be ON):

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

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


Fuel injection and some other systems are controlled by the Engine ECM (arrow) located on topof 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." Besure 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 tothe secondary fuel filters.

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

The ECM in earlier 3500 engines had one 70-pin connector and cannot be reprogrammed withthe WinFlash application in ET. Reprogramming of the earlier ECM requires a replacement ofthe 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 timingcalibration, a timing calibration sensor (magnetic pickup) is installed in the flywheel housingand connected to the timing calibration connector.

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

Timing calibration improves fuel injection accuracy by correcting for any slight tolerancesbetween 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 componentsare 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 EngineECM uses the atmospheric pressure sensor as a reference for calculating boost and air filterrestriction.

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

The Engine ECM also uses the atmospheric pressure sensor as a reference when calibrating allthe 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 DCVoltage output signal that varies between 0.2 and 4.8 Volts DC with an operating pressure rangebetween 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 thesensor connector. Set the meter to read "DC Volts." The DC Voltage output of the atmosphericpressure 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 sensorsignals the speed, direction, and position of the camshaft by counting the teeth and measuringthe 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 theEngine ECM does not receive an input signal from the engine speed/timing sensor, the enginewill not run.

The engine speed/timing sensor receives a regulated 12.5 ± 1.0 Volts from the Engine ECM. Tocheck the output signal of the speed/timing sensor, connect a multimeter between Pins B and Cof the speed/timing sensor connector. Set the meter to read "Frequency." The frequency outputof 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. Thepassive speed sensor uses the passing teeth of the flywheel to provide a frequency output. Thepassive speed sensor sends the engine speed signal to the Transmission/Chassis ECM and theBrake ECM.

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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 multimeterbetween 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 crankingtest to prevent the engine from starting. The cranking speed and frequency output willvary depending on weather and machine conditions. When viewing engine speed in theET 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. Ifthe Engine ECM detects a fault in the throttle position sensor, the throttle back-up switch (seeVisual 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. Thethrottle position sensor output signal is a Pulse Width Modulated (PWM) signal that varies withthrottle 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 Band C of the throttle position sensor connector. Set the meter to read "Duty Cycle." The dutycycle 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 earliertrucks must be programmed to a 10 to 50% throttle position. The setting is changed inthe Engine ECM configuration screen with ET.

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Shown is the top of a cylinder head with the valve cover removed. The most important outputfrom the Engine ECM is the Electronic Unit Injection (EUI) injector solenoid (arrow). Oneinjector is located in each cylinder head. The engine control analyzes all the inputs and sends asignal 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 isenergized. Engine speed is determined by controlling the duration that the injector solenoid isenergized.

3500B injectors are calibrated during manufacturing for precise injection timing and fueldischarge. After the calibration, a four-digit "E-trim" code number is etched on the injectortappet 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 enteredinto 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 injectorsand 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 EngineECM. If the new trim code is not entered, the previous injector's characteristics are used. Theengine will not be harmed if the new code is not entered, but the engine will not provide peakperformance.

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61

The 3500B engines have many improvements over the original 3500 engines. Some of theimprovements are accomplished by adding additional switch and sensor inputs to the EngineECM. 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).


3500B IMPROVEMENTSINPUT SWITCHES AND SENSORS

- Coolant Flow- Rear Aftercooler Temperature- Engine Oil Level- Turbocharger Temperature- Engine Oil Filter Pressure / Restriction- Engine Fan Speed- Fuel Filter Restriction- Air Conditioner Compressor Pressure- Crankcase Pressure

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

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The crankcase pressure sensor (arrow) is located on the right side of the engine above the engineoil cooler. The crankcase pressure sensor provides an input signal to the Engine ECM. TheECM 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 pressureevent will be logged. No factory password is required to clear this event.

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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.


3500B IMPROVEMENTSPREVIOUS LOGGED EVENTS

- Air Filter Restriction

- Low Oil Pressure

- High Coolant Temperature

- Engine Overspeed

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Additional events logged by the 3500B ECM are:

Oil filter restriction: Greater than 70 kPa (10 psi), no factory password required. Greater than200 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%. Factorypassword required.

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

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 factorypassword required.


3500B IMPROVEMENTSADDITIONAL LOGGED EVENTS

- Oil Filter Restriction - Low Coolant Flow

- Fuel Filter Restriction - User Defined Shutdown

- High Exhaust Temperature - Low Boost Pressure

- High Aftercooler Temperature - High Boost Pressure

- Engine Oil Level Low - Pre-lube Override

- High Crankcase Pressure

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 theEngine ECM at Connector J1 Pin 19, a user defined shutdown will occur. Factory passwordrequired.

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 theother systems controlled by the ECM are:

Ether Injection: The Engine ECM will automatically inject ether from the ether cylindersduring cranking. The duration of automatic ether injection depends on the jacket water coolanttemperature. The duration will vary from 10 to 130 seconds. The operator can also inject ethermanually with the ether switch in the cab on the center console (see Visual No. 48). The manualether injection duration is 5 seconds. Ether will be injected only if the engine coolanttemperature 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 canbe added in front of the radiator. Installing shutters in front of the radiator allows the engine towarm up to operating temperature quicker. If a truck is equipped with the attachment radiatorshutter control, the shutters are controlled by the Engine ECM.


3500B IMPROVEMENTSSYSTEMS CONTROLLED BY ECM

- Ether Injection

- Radiator Shutter Control

- Cold Mode

- Cold Cylinder Cutout

- Engine Start Function

- Engine Oil Pre-lubrication

- Variable Speed Fan Control

- Engine Oil Renewal System

Cool Engine Elevated Idle: The Engine ECM provides an elevated engine idle speed of 1300rpm when the engine coolant temperature is below 60°C (140°F). The rpm is gradually reducedto 1000 rpm between 60°C (140°F) and 71°C (160°F). When the temperature is greater than71°C (160°F), the engine will operate at low idle (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion and overcooling. Totemporarily reduce the elevated idle speed, the operator can release the parking brake or depressthe 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. TheECM 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 enginespeed during a cylinder cutout. The ECM averages the fuel delivery and analyzes the fuel ratechange 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 roughuntil the coolant temperature increases above the Cold Mode temperature. This condition isnormal, 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 theTransmission/Chassis ECM. The Engine ECM provides signals to the Transmission/ChassisECM regarding the engine speed and the condition of the engine pre-lubrication system. TheTransmission/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 above300 rpm.


Engine Oil Pre-lubrication (attachment): Engine oil pre-lubrication is controlled by the EngineECM and Transmission/Chassis ECM. The Engine ECM energizes the pre-lubrication pumprelay located behind the cab (see Visual No. 53) The relay behind the cab then energizes thepre-lube relay (1) on the front engine mount. The Engine ECM signals theTransmission/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 twoseconds. The Transmission/Chassis ECM will begin the pre-lube cycle. While the pre-lubecycle is active, turn the key start switch to the OFF position. Within 10 seconds, turn the keystart switch back to the CRANK position. The Transmission/Chassis ECM will energize thestarter relay.

If the engine oil pre-lubrication system is bypassed using the above procedure, the Engine ECMwill 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 theEngine ECM.

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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 theengine. The ECM sends a signal to the variable speed fan control solenoid valve (1) and engineoil 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 temperatureregulator (thermostat) housing. The ECM uses the coolant temperature sensor information asthe main parameter to control the fan speed. The aftercooler temperature sensor, air conditionerpressure sensor and brake cooling oil temperature sensors are also used as inputs to determinethe required fan speed. A speed sensor (not shown) is located behind the fan pulley and informsthe ECM of the current fan speed.

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

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

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

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Engine Oil Renewal System (attachment): Located on the right side of the engine are thecomponents of the engine oil renewal system. Engine oil flows from the engine block throughan oil filter (1) to the engine oil renewal solenoid valve (2). When the solenoid is energized andde-energized, a small amount of oil flows from the engine oil renewal solenoid valve into thefuel line that returns to the fuel tank. The engine oil mixes with the fuel in the tank and flowswith 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 engineoil renewal system filter, the primary fuel filter, and the secondary fuel filters must all bechanged at 500 hour intervals. The engine oil should be changed at least once per year or 4000service meter hours.

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

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12

The Engine ECM regulates the amount of oil that is injected by the engine oil renewal solenoidvalve. Several parameters must be met before the ECM will allow the injection of oil throughthe 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).- Oil filter differential pressure at high idle with warm oil is less than 70 kPa (10 psi).- 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 amountof 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 isequivalent to 0.25% to 0.75% oil to fuel ratios.

INSTRUCTOR NOTE: For more detailed information on servicing the oil renewalsystem, 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 SlaveECM 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 1.25seconds and turned OFF for 1.25 seconds for a total cycle time of 2.5 seconds. How many timesthe solenoid is turned ON and OFF will determine the volume of oil that is injected. Oil isinjected 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 thepiston to the right. The volume of oil that is trapped between the right side of the piston and thecheck ball compresses the spring and opens the passage to the fuel return line. When thesolenoid is turned OFF, engine oil flows to the right side of the piston and pushes the piston tothe left. The volume of oil that is trapped between the left side of the piston and the check ballcompresses the spring and opens the passage to the fuel return line. The volume of delivery isequal to 3.04 ml/cycle (0.1 oz/cycle).


ON

Piston

To FuelReturn

From EngineOil Gallery

OFF

Piston

From EngineOil Gallery

OIL RENEWAL SOLENOID VALVE

To FuelReturn

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) hasbeen added above the radiator. The shunt tank provides a positive pressure at the coolant pumpinlets to prevent cavitation during high flow conditions.

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

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

A coolant level switch (3) is located on each side of the shunt tank to monitor the coolant levelof both cooling systems (guard removed for viewing switch). The coolant level switchesprovide 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 acooling system overheats or if coolant is leaking from a relief valve, clean or replace the reliefvalve.

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

Two coolant level switches (2) are located on the top tank to monitor the coolant level of bothcooling systems. The coolant level switches provide input signals to the VIMS, which informsthe 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 (approximately60% of the total capacity). The jacket water cooling system temperature is controlled bytemperature 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 forincreased horsepower.

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3

The jacket water pump (1) is located on the right side of the engine. The pump draws coolantfrom the bypass tube (2) until the temperature regulators (thermostats) open. The thermostatsare 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 ECMwill log an event that requires a factory password to clear.

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3

Coolant flows from the jacket water pump, past the coolant flow warning switch (1), andthrough 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 providesthe 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. Afactory password is required to clear this event.

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

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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 rearbrake oil coolers to both sides of the engine cylinder block. Coolant flows through the engineblock and through the cylinder heads. From the cylinder heads, the coolant flows to thetemperature regulators and either goes directly to the water pump through the bypass tube or tothe radiator (depending on the temperature of the coolant).

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2 3

76

Shown is the jacket water cooling circuit. Coolant flows from the jacket water pump throughthe 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 eithergoes directly to the water pump through the bypass tube or to the radiator (depending on thetemperature of the coolant).

The shunt tank (789C only) increases the cooling capacity and provides a positive pressure at thecoolant 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 thesystems 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


Transmission Oil Cooler

Engine Oil Cooler

Hoist, Converter andBrake Oil Cooler

JACKET WATER COOLANT FLOW ThermostatHousing

RadiatorJacket

Water Pump

ShuntTank

Hoist, Converter andBrake Oil Cooler

EngineBlock

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

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

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3

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

The Engine ECM also provides the input signal to the VIMS, which informs the operator of theaftercooler 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 ofthe engine.

Coolant flows through the front brake oil cooler to the aftercooler section of the radiator. Theaftercooler 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 frontbrakes. Diverting oil around the cooler provides lower temperature aftercooler air during highpower demands (when climbing a grade with the brakes RELEASED, for example).

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79

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

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

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 aftercoolerwater pump inlet to prevent cavitation during high flow conditions.

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


Radiator

AftercoolerWater Pump

AirCompressor

Front BrakeOil Cooler

DiverterValve

ShuntTank

Aftercooler

AFTERCOOLER COOLANT FLOW

Lubrication System

Shown is the 3512B engine used in the 785C truck. The engine oil pump is located behind thejacket water pump on the right side of the engine. The pump draws oil from the oil pan througha 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 theoil 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 coldstarts 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 ScheduledOil Sampling (S•O•S) tap (4).

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

Engine oil is added at the fill tube (1) and checked with the dipstick (2). A bypass valve foreach filter is located in each oil filter base. Engine oil samples can be taken at the Scheduled OilSampling (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 oilpressure after the filters. The sensors send input signals to the Engine ECM. The ECM providesthe input signal to the VIMS, which informs the operator of the engine oil pressure. Usedtogether, the two engine oil pressure sensors inform the operator if the engine oil filters arerestricted.

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 clearthis event.

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4

Shown is the 3512B engine used in the 785C truck. The 3512B engine uses three oil filterslocated on the left side of the engine. The 3512B engine also has a fitting (arrow) that can beused 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 theengine.

NOTICE

When changing the engine oil filters, drain the engine oil trapped above the oil filtersthrough the fitting (arrow) to prevent spilling the oil. Oil added to the engine through thefitting 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 systemand cause damage to the engine.

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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 theoil pan to the main sump.

Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. Thebypass valve for the engine oil cooler permits oil flow to the system during cold starts when theoil 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 entersthe engine cylinder block to clean, cool and lubricate the internal components and theturbochargers.

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


ENGINE OIL SYSTEM

EngineOil Cooler

EngineOil Filters

EngineOil Pump

BypassValve

EngineOil Renewal

System Solenoid

To FuelTank

ScavengePump

Fuel System

The fuel tank is located on the left side of the truck. Fuel is pulled from the tank through thefuel heater (not shown), if equipped, and through the primary fuel filter (1) by the fuel transferpump 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 ultrasonicsignal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonicsignal to return is converted to a Pulse Width Modulated (PWM) signal. The PWM signalchanges 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) isshown 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 than10%.

The fuel level sensor receives 24 Volts from the VIMS. To check the supply voltage of thesensor, 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 withthe fuel level. To check the output signal of the fuel level sensor, connect a multimeter betweenPins 2 and 4 of the fuel level sensor connector. Set the meter to read "Duty Cycle." The dutycycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depthand 84% at 2000 mm (78.8 in.) of fuel depth.

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

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

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1

2

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

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

If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. Nofactory 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 injectorsreceive 4 1/2 times the amount of fuel needed for injection. The extra fuel is used for cooling.

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

86


12

Fuel flows from the fuel filter base through the steel tubes (1) to the EUI fuel injectors. Returnfuel from the injectors flows through the fuel pressure regulator (2) before returning to the fueltank. 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 fuelfilter by the fuel transfer pump. Fuel flows from the transfer pump through the Engine ECM tothe secondary fuel filters.

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

If equipped with the engine oil renewal system, engine oil flows from the engine block throughan oil filter to the engine oil renewal system manifold. A small amount of oil flows from theengine oil renewal system manifold into the return side of the fuel pressure regulator. Theengine 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 beburned.


FUEL SYSTEM

FuelTank

FuelTransfer

Pump

PrimaryFuelFilter

SecondaryFuel Filters

CylinderHead

CylinderHead

FuelPressureRegulator

EngineEcm

FuelPrimingPump

FuelHeater

EngineBlock

Engine OilRenewalSolenoid

Air Induction and Exhaust System

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

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

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

Two filter elements are installed in the filter housings. The large element is the primary elementand 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 theturbochargers. The Engine ECM uses the turbocharger inlet pressure sensor in combination withthe atmospheric pressure sensor to determine air filter restriction. The ECM provides the inputsignal 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 belogged, and the ECM will derate the fuel delivery (maximum derating of 20%) to preventexcessive exhaust temperatures. A factory password is required to clear this event. If theEngine ECM detects a turbocharger inlet pressure sensor fault, the ECM will derate the engineto the maximum rate of 20%. If the Engine ECM detects a turbocharger inlet and atmosphericpressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of40%.

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. Theduration will vary from 10 to 130 seconds. The operator can also inject ether manually with theether switch in the cab on the center console (see Visual No. 48). The manual ether injectionduration is 5 seconds. Ether will be injected only if the engine coolant temperature is below10°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 fourturbochargers (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 sideof the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, andthe mufflers.

The clean air from the filters enters the compressor side of the turbochargers. The compressedair 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 theturbochargers. 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 exhausttemperature.

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

If the exhaust temperature is above 750°C (1382°F), the Engine ECM will derate the fueldelivery to prevent excessive exhaust temperatures. The ECM will derate the engine by 2% foreach 30 second interval that the exhaust temperature is above 750°C (1382°F) (maximum derateof 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 sideof the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, andthe mufflers.

The clean air from the filters enters the compressor side of the turbochargers. The compressedair 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.


Muffler

From AirFilters

Aftercooler

3512BAIR INDUCTION

ANDEXHAUST SYSTEM

From AirFilters

94

POWER TRAIN

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

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

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


POWER TRAIN

785C

Torque Converter

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

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

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

A Converter Output Speed (COS) sensor (5) sends an input signal to the Transmission/ChassisECM. The Transmission/Chassis ECM uses the information to calculate shift times for thetorque converter lockup clutch and the transmission clutches. The shift time information is sentto 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 andimpeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationary andmultiplies the torque transfer between the impeller and the turbine. The output shaft rotatesslower than the engine crankshaft, but with increased torque.


Stator

TORQUE CONVERTERCONVERTER DRIVE

Lockup Piston

Torque ConverterLockup Oil Passage

Turbine Impeller

FreewheelAssembly

Torque ConverterInlet Oil

97

In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine tothe 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 thehousing and will freewheel at approximately the same rpm.


Stator

TORQUE CONVERTERDIRECT DRIVE

Lockup Piston

Torque ConverterLockup Oil Passage

Turbine Impeller

FreewheelAssembly

Torque ConverterInlet Oil

Torque Converter Hydraulic System

The three (785C) or four (789C) section torque converter pump is located at the bottom rear ofthe 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 firstsection of the pump through a screen behind the access cover (5) and returned to the hydraulictank.

98


12

3

4 5

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

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

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. Thetorque converter inlet relief pressure can be measured at this valve by removing a plug andinstalling a pressure tap. Inlet relief pressure should not exceed 930 ± 35 kPa (135 ± 5 psi) athigh idle when the oil is cold. Normally, the inlet relief pressure will be slightly higher than theoutlet 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 bescavenged. Most of the oil in the torque converter is used to provide a fluid coupling and flowsthrough the torque converter outlet relief valve (2). The outlet relief valve maintains theminimum pressure inside the torque converter. The main function of the outlet relief valve is tokeep the torque converter full of oil to prevent cavitation. The outlet relief pressure can bemeasured 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 theTransmission/Chassis ECM. The Transmission/Chassis ECM sends a signal to VIMS, whichinforms 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 converteroutlet screen (1) located outside the left frame.

A torque converter outlet screen bypass switch (2) provides an input signal to the VIMS, whichinforms 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 theengine.

Oil flows from the parking brake release section of the torque converter pump to the parkingbrake 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 signalto 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 flowingthrough the front brake oil cooler (2). When the retarder or service brakes are ENGAGED, theoil is diverted through the cooler to the brakes. When the brakes are RELEASED, the oilbypasses the cooler and flows directly to the brakes.

Diverting oil around the cooler provides lower temperature aftercooler air during high powerdemands (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). Theparking brake release section of the torque converter pump provides supply oil for severalpurposes:

- 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, torqueconverter 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 the789C 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 throughthe inlet port (1). When the lockup clutch solenoid (located on the transmission housing) isenergized by the Transmission/Chassis ECM, transmission pump supply oil (signal oil) entersthe 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 torqueconverter lockup. The lockup clutch valve then supplies oil to ENGAGE the lockup clutch inthe torque converter.

Torque converter lockup clutch pressure can be measured at the tap (3). Torque converterlockup clutch pressure should be 2135 ± 70 kPa (310 ± 10 psi) at 1300 rpm or higher. Do notcheck the torque converter lockup clutch pressure below 1300 rpm.

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

Using the information from the Transmission/Chassis ECM, the VIMS calculates if any slippageexists in the torque converter lockup clutch or any transmission clutches and stores thisinformation in the VIMS main module. This information can be downloaded from the VIMSwith 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 thepressure reduction valve flows through cross-drilled orifices in the spool, past a check valve, andenters the slug chamber. The check valve dampens spool movement and reduces the possibilityof valve chatter and pressure fluctuation. Oil pressure moves the slug in the right end of thespool to the right and the spool moves to the left against the spring force. The slug reduces theeffective area on which the oil pressure can push. Because of the reduced effective area, asmaller, more sensitive spring can be used. Pilot pressure will be equal to the force of the springon 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 tothe relay valve. Before moving the selector piston, the pilot oil moves a shuttle valve to theright, which closes the lower left drain passage and opens the check valve. Oil then flows to theselector piston. Moving the selector piston blocks the upper drain passage, and the load pistonsprings are compressed.


LockupSolenoid

FromTransmissionCharge Pump

Relay Valve

LockupReducing

Valve

LockupModulation

Valve

Lockup ClutchPilot Pressure

(RV)

To LockupClutch (LU)

From Parking BrakeRelease Pump (PMP)

TORQUE CONVERTER LOCKUP CLUTCH CONTROLDIRECT DRIVE

ShuttleValve

SelectorPiston

ToTransmission

Lube

ToStation

"D"

Signal Oil

When the solenoid is energized, supply oil from the parking brake release pump is reduced toprovide the lockup clutch pressure. Lockup clutch pressure depends mainly on the force of theload piston valve springs. When the solenoid is energized, pilot oil moves the selector pistondown against a stop. When the load piston that compresses the springs is at the top against theselector 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 graduallyuntil the load piston stops. Maximum lockup clutch pressure is then reached. The gradualincrease 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 abovethe load piston. The load piston orifice meters the flow of oil to the load piston chamber anddetermines the modulation time.

Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is notadjustable. If the primary pressure is correct and final lockup clutch pressure is incorrect, theload piston should be checked to make sure that it moves freely in the selector piston. If theload 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 torqueconverter hydraulic system on the 789C truck.

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

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

The parking brake release pump section sends oil through the parking brake release filter to theparking brake release valve and the torque converter lockup clutch valve. Most of the oil flowsthrough 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 thetwo oil coolers located on the right side of the engine to the rear brakes.


TORQUE CONVERTERHYDRAULIC SYSTEM

FrontBrakes

Torque ConverterCharging Filter


ParkingBrake

ReleaseValve

DiverterValve

ConverterOutletScreen

ParkingBrakeFilter

Rear BrakeOil Coolers

RearBrakes

To HoistSolenoidManifold

ConverterScavenge

Screen

OutletRelief Valve

InletRelief Valve

ConverterLockupValve

Transmission and Transfer Gears

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

The transmission (2) is located between the transfer gears and the differential (3). Thetransmission 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 thetransmission flows through the differential and is divided equally to the final drives in the rearwheels. 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). Transmissionlube oil flows through the transfer gears and the transmission to cool and lubricate the internalcomponents.

The transmission lube pressure relief valve is in the transmission case near the transmissionhydraulic control valve. The relief valve limits the maximum pressure in the transmission lubecircuit. 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). AtLOW 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. Asmall shaft runs from the speed sensor location through the entire length of the transmission andengages the transmission output shaft. The transmission speed sensor signal serves manypurposes. 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 engagedclutches. The transmission provides six FORWARD speeds and one REVERSE speed.


1 2 3

45 6

POWER SHIFT PLANETARY TRANSMISSION

Transmission Hydraulic System

The transmission pump pulls oil through a suction screen from the transmission tank (seeVisuals 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 locatedinside 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 bottomof 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 screensshould 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 VisualNo. 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 topof the transmission. A transmission oil temperature sensor (2) is located in the tube between thetransmission charging filter and the transmission control valve. The temperature sensor providesan input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends asignal 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 transfergears. Transmission lube oil flows through the transfer gears and the transmission to cool andlubricate the internal components.

An oil filter bypass switch is located on each filter. The oil filter bypass switches provide inputsignals to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to theVIMS, 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 thetransmission oil cooler bypass valve (1) to the transmission oil cooler (2). The bypass valve forthe transmission oil cooler permits oil flow to the system during cold starts when the oil is thickor if the cooler is restricted.

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

113


1

2

The transmission charging pump supplies oil to the transmission hydraulic control valve and theshift solenoids through the inlet port (1). Excess transmission charging oil either drops to thebottom 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 ECMwhen DIRECT DRIVE (lockup clutch ENGAGED) is required. Transmission charge pumpsupply (signal) oil flows through the small hose (4) to the lockup clutch control valve. Thelockup clutch control valve then engages the lockup clutch.

The transmission charging pressure relief valve is part of the transmission hydraulic controlvalve. 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 controlsthe pressure that is directed to the selector pistons in each of the clutch stations. Thetransmission priority valve pressure is 1720 kPa (250 psi).

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

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

At LOW IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be2515 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 extendthe life of the transmission clutch seals. At 1300 rpm in DIRECT DRIVE, the clutch supplypressure should be 2020 + 240 - 100 kPa (293 + 35 - 15 psi). The corresponding transmissioncharge 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 8T5200Signal Generator/Counter can be used to shift the transmission during the diagnostic tests. If aSignal Generator is not available, disconnect the upshift and downshift solenoids and rotate therotary selector spool manually by inserting a 1/4 in. ratchet extension through the transmissioncase.


116

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


DownshiftSolenoid

UpshiftSolenoid

LockupSolenoid

F

G

H

A

B

C

RotarySelector

Spool

NeutralizerValve

PriorityReduction

Valve

DownshiftPressure

UpshiftPressure

Transmission Case

TransmissionTank

ChargingPump

LubePump Scavenge

Pump

CoolerBypassValve

OilCooler

LubricationRelief Valve

Pump Pressure

To Torque ConverterRelay Valve

Selector Valve GroupRelief Valve

Lockup DualStage Relief Valve

LubePressure

On

Pressure ControlGroup

Pilot Oil Pressure

D

E

Rotary Actuator

N1

3

Filters

TRANSMISSION ICM HYDRAULIC SYSTEM

117

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

The three-section transmission pump is mounted on the rear of the pump drive, which is locatedinside 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 bottomof the transmission. The scavenged oil from the transmission is sent to the transmission tank.


TransmissionCharging Filter

SignalTo LockupValve Relay

Magnetic ScavengeScreens

TransmissionLube Filter

TransmissionOil Cooler

TransmissionPump

LubePort

785C / 789C TRANSMISSION HYDRAULIC SYSTEM

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 topof the transmission. Transmission charging oil flows from the transmission control valve andjoins 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 thetransmission oil cooler. Oil flows from the transmission oil cooler to the transfer gears and thetransmission to cool and lubricate the internal components.


Differential

Shown is the differential removed from the rear axle housing. The rear axle cooling and filtersystem starts with a rear axle pump (1) that is driven by the differential. Since the pump rotatesonly 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 ontop of the differential housing to a filter mounted on the rear of the axle housing. Oil then flowsfrom the filter back to the valve located on top of the differential housing. Oil then flows fromthe 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 reducingthe 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 controlvalve (2). A differential oil temperature sensor (3) and pressure sensor (4) are located on thetemperature and flow control valve. The sensors provide input signals to the Brake ECM. TheBrake ECM sends signals to the VIMS.

The differential temperature sensor input signal is used to warn the operator of a high rear axleoil 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 LOWrear 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 thedifferential 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 thedifferential 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 oilis cold. When the oil temperature is below 43°C (110°F), the valve is OPEN and allows oil toflow to the rear axle housing. When the oil temperature is above 43°C (110°F), the valve isCLOSED and all the oil flows through the filter to a flow control valve located in thetemperature and flow control valve. The temperature and pressure control valve is also thesystem main relief valve. If the pressure exceeds 690 kPa (100 psi), the temperature andpressure 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 differentialbearings.

Oil flows from the temperature and flow control valve to the differential oil filter mounted onthe rear of the axle housing. Oil then flows from the filter back to the temperature and flowcontrol valve. Some of the oil that flows from the temperature and flow control valve flowsthrough 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) (onebehind differential filter) provide input signals to the Brake ECM. The Brake ECM sendssignals to the VIMS.

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

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

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

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

120


1

23

121

Shown is a schematic of the rear axle oil cooling and filter system. The differential oil pumppulls oil from the bottom of the rear axle housing through a suction screen. Oil flows from thepump 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 controlvalve, prevents high oil pressure when the rear axle oil is cold. When the oil temperature isbelow 43°C (110°F), the valve is OPEN and allows oil to flow to the rear axle housing. Whenthe oil temperature is above 43°C (110°F), the valve is CLOSED and all the oil flows throughthe differential oil filter and the oil cooler (if equipped) to a flow control valve, which is alsopart of the temperature and flow control valve.

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

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


Oil Cooler OilFilter

Temperature /Pressure

Control Valve

REAR AXLEOIL COOLING AND FILTER SYSTEM

Temperature andFlow Control Valve

DifferentialOil Pump

SuctionScreen

Rear Axle

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Final Drives

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

The first reduction carrier is splined to the second reduction sun gear. The second reduction sungear 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 alsorotates.

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


First ReductionRing Gear

Second ReductionRing Gear

Second ReductionCarrier

Second ReductionSun Gear

Second ReductionPlanetary Gear

First ReductionPlanetary Gear

First ReductionSun Gear

First ReductionCarrier

FINAL DRIVE

Transmission/Chassis Electronic Control System

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

The transmission control used in the "C" Series trucks performs the transmission controlfunctions, plus some other machine functions (hoist control). Because of the added functionalityof 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 AnalyzerProgrammer (ECAP) or a laptop computer with the Electronic Technician (ET) softwareinstalled. ET is the tool of choice because the Transmission/Chassis ECM can be reprogrammedwith 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-pinconnectors, 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.

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

The Transmission/Chassis ECM receives information (electrical signals) from various inputcomponents 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 thetransmission 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, andothers.

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


Hoist Lower Solenoid

Back-up AlarmRelay

StarterSolenoid

Shift LeverPosition Switch

Key Start Switch

Upshift Solenoid

Lockup Solenoid

BodyPosition Sensor

INPUT COMPONENTS OUTPUT COMPONENTS

Transmission GearSwitch

Transmission OutputSpeed Sensor

Parking/secondary BrakePressure Switch

Service / RetarderBrake

Pressure Switch

Converter OutputSpeed Sensor

Engine OutputSpeed Sensor

Hoist LeverPosition Sensor

Brake ECM

Engine ECM

Electronic Service Tool

CAT Data Link

VIMS

Downshift Solenoid

Hoist Raise Solenoid

Auto Lube Solenoid

Low SteeringPressure Switch

Transmission ChargeFilter Switch

Transmission OilTemp Sensor

Hoist Screen Switch

Transmission LubeFilter Switch

Torque ConverterOil Temp Sensor

Body Up Lamp

"C" SERIES TRUCKTRANSMISSION / CHASSIS ELECTRONIC CONTROL SYSTEM

The Engine Electronic Control, the Brake Electronic Control System (ARC and TCS), the VitalInformation Management System (VIMS) and the Transmission/Chassis Electronic ControlSystem all communicate through the CAT Data Link. Communication between the electroniccontrols 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 ECMsignals the Engine ECM to reduce or increase engine fuel during a shift to lower stress to thepower 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 onthe "B" Series trucks have been moved to provide input signals to the Transmission/ChassisECM and the Brake ECM. Sensors and switches that were in the VIMS and now provide inputsignals 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 thecab in the shift console and provides input signals to the Transmission/Chassis ECM. The shiftlever switch controls the desired top gear selected by the operator. The shift lever switch inputsconsist 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 positionresults in two of the five wires sending a ground signal to the Transmission/Chassis ECM. Theother three wires remain open (ungrounded). The pair of grounded wires is unique for each shiftlever position. The sixth wire is the "Ground Verify" wire, which is normally grounded. TheGround Verify wire is used to verify that the shift lever switch is connected to theTransmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM todistinguish between loss of the shift lever switch signals and a condition in which the shift leverswitch is between detent positions.

To view the shift lever switch positions or diagnose problems with the switch, use the VIMSmessage 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 shoulddisplay 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 positionnumbers on the shift console by loosening the three nuts (2) and rotating the lever. The positionof the shift lever switch is also adjustable with the two screws (3).

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The transmission gear switch (1) provides input signals to the Transmission/Chassis ECM. Thetransmission 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 foreach position of the transmission gear switch. Each transmission gear switch position results intwo of the five wires sending a ground signal to the Transmission/Chassis ECM. The other threewires 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 Verifywire is used to verify that the transmission gear switch is connected to the Transmission/ChassisECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish betweenloss of the transmission gear switch signals and a condition in which the transmission gearswitch is between gear detent positions. Earlier transmission gear switches use a wiper contactassembly that does not require a power supply to Pin 4 of the switch. Current transmission gearswitches are Hall-Effect type switches. A power supply is required to power the switch. Asmall magnet passes over the Hall cells, which then provide a non-contact position switchingcapability. The Hall-Effect type switch uses the same 24-Volt power supply used to power theTransmission/Chassis ECM. The solenoid outputs provide +Battery voltage to the upshiftsolenoid (2), the downshift solenoid (3) or the lockup solenoid (4) based on the inputinformation from the operator and the machine. The solenoids are energized until thetransmission actual gear switch signals the Transmission/Chassis ECM that a new gear positionhas been reached.

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4

The Transmission Output Speed (TOS) sensor (arrow) is located on the transfer gear housing onthe input side of the transmission. Although the sensor is physically located near the input endof the transmission, the sensor is measuring the speed of the transmission output shaft. Thesensor 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 squarewave signal of approximately 10 Volts amplitude. The frequency in Hz of the square wave isexactly equal to twice the output shaft rpm. The signal from this sensor is used for automaticshifting of the transmission. The signal is also used to drive the speedometer and as an input toother electronic controls.

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

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

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

- Signals the Transmission/Chassis ECM to use elevated shift points, which providesincreased engine speed during downhill retarding for increased oil flow to the brakecooling 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 rapidupshift-downshift sequence or a rapid downshift-upshift sequence (transmission hunting). Thetimer is active during normal operation. It is overridden when either the service/retarder orparking/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 switchwithin two hours of operation time.

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

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5

The parking/secondary brake switch (2) is in the parking/secondary brake air pressure line. Thenormally open switch is closed during the application of air pressure. The purpose of the switchis to signal the Transmission/Chassis ECM when the parking/secondary brakes are ENGAGED.Since the parking/secondary brakes are spring engaged and pressure released, theparking/secondary brake switch is closed when the brakes are RELEASED and opens when thebrakes are ENGAGED. This signal is used to override the anti-hunt timer for rapiddownshifting 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 switchwithin one hour of operation time.

Many relays (3) are located behind the cab. Some of these relays receive output signals fromthe Transmission/Chassis ECM, and the relays turn on the desired function. The back-up alarmrelay 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 providesa 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 thecompartment behind the cab. The low air pressure sensor provides an input signal to the BrakeECM. The Brake ECM sends a signal to the VIMS, which informs the operator of the systemair pressure condition.


The body position sensor (1) is located on the frame near the left body pivot pin. A rodassembly (2) is connected between the sensor and the body. When the body is raised, the rodrotates the sensor, which changes the Pulse Width Modulated (PWM) signal that is sent to theTransmission/Chassis ECM. The adjustment of the rod between the sensor and the body is veryimportant. 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 iscalibrated 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 shoulddisplay zero degrees. If the position is greater than zero degrees, the sensor rod may have to beadjusted.

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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 willshift when the body is UP. The body up gear limit value is programmable from FIRST toTHIRD gear using the ECAP or ET service tool. The Transmission/Chassis ECM comes fromthe factory with this value set to FIRST gear. When driving away from a dump site, thetransmission will not shift past the programmed gear until the body is down. If the transmissionis 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 controlvalve. When the body is being lowered, the Transmission/Chassis ECM signals the hoistLOWER 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 ismoving 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. Tocheck the supply voltage to the sensor, connect a multimeter between Pins A and B of theconnector. Set the meter to read "DC Volts."

The body position sensor output signal is a Pulse Width Modulated (PWM) signal that varieswith the body position. To check the output signal of the body position sensor, disconnect therod 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 smoothlybetween 3% and 98% when rotated. The duty cycle should be low when the body is DOWNand high when the body is UP.


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STEERING SYSTEM

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

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

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


STEERING

789C

131

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

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

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

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


Solenoid andRelief Valve

ReturnManifold

SteeringDirectional

Valve

HandMetering Unit

Low SteeringPressure Switch

High SteeringPressure Switch

RL

P

T

LS

Piston Pump

AccumulatorCharging Valve

789C STEERING SYSTEMNO STEER / MAXIMUM FLOW

CaseDrainFilter

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 whichdirection the steering wheel is turned, oil will flow to the head end of one steering cylinder andto the rod end of the other cylinder. The action of the oil on the pistons and rods in the steeringcylinders causes the wheels to change direction. Displaced oil from the steering cylinders flowsthrough the back pressure valve in the steering directional valve and returns through the mainsteering oil filter to the tank.


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Oil from the steering pump flows through a one-way check valve to the solenoid and relief valvereturn manifold and is then sent to the accumulators and the Hand Metering Unit (HMU). The785C truck does not use a steering directional valve. Oil from the HMU flows through acrossover 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 flowthrough the HMU in the HOLD position provides a "thermal bleed" condition, which preventsthermal seizure of the HMU (sticking steering wheel).

The crossover relief valves protect the steering cylinders and oil lines from pressure surges whenthe steering wheel is in the HOLD position by equalizing the oil pressure between the head endsand 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 oilfilter.


CrossoverReliefValves

HandMetering

Unit

PistonPump

PumpSwitch

Solenoid andRelief Valve

Return Manifold

Case DrainFilter

785C STEERING SYSTEMHOLD

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 andADD OIL markings of the upper sight gauge (l). When the engine is running and theaccumulators are fully charged, the oil level should not be below the ENGINE RUNNINGmarking of the lower sight gauge (2). If the ENGINE RUNNING level is not correct, check thenitrogen charge in each accumulator. A low nitrogen charge will allow excess oil to be stored inthe accumulators and will reduce the secondary steering capacity.

A combination vacuum breaker/pressure relief valve is used to limit the tank pressure. Beforeremoving the fill cap, be sure that the engine was shut off with the key start switch and the oilhas returned to the tank from the accumulators. Depress the pressure release button (3) on thebreather 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 thepump returns to the tank through the filter (4). The remaining steering system oil returns to thetank through the main steering filter (5). Both filters are equipped with bypass valves to protectthe 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 anAuxiliary Power Unit (APU). The APU will provide supply oil from the steering tank at theconnector to charge the steering accumulators. Steering capability is then available to tow thetruck.

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5

6

7

The steering oil temperature sensor (7) provides an input signal to the VIMS, which informs theoperator 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 SpecialInstructions "Using 1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Usingthe 1U5525 Attachment Group" (Form SEHS8880).


The piston-type steering pump (1) for the 785C truck is mounted to the pump drive. The pumpdrive 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 flowto the accumulators for steering system operation.

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

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135

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


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136

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

As the accumulators fill, the pressure of the oil through the pump outlet increases. The pumpsupply pressure will increase until the pressure of the oil in the pump passage in the pumpcompensator valve is high enough to overcome the spring force on the compensator spool. Thespool then moves to the left and opens the passage to the control piston. This movement occurswhen 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 compensatorspool spring. Remove the plug and add shims to increase the pressure setting. Remove shims tolower the setting.


ToControl Piston

Drain Passages

PUMP COMPENSATOR VALVE

MAXIMUM PUMP FLOW

ToControl Piston

Drain Passages

MINIMUM PUMP FLOW

FromPump

FromPump

137

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

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

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


Swashplate PistonSupply Passage

for Pump

Output PassageFrom Pump

PressureCompensator Valve

Control Piston

785C STEERING PUMP MINIMUM FLOW

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

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

The steering pump will produce flow at high pressure until the steering accumulators arecharged 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 loadsensing 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) "thermalbleed," 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.

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When the pressure in the accumulators decreases to the CUT-IN pressure, the accumulatorcharging valve blocks the load sensing signal line to the load sensing controller from returningto 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 supplypressure is measured at this tap during LOW PRESSURE STANDBY, a gauge acceptable fortesting maximum steering system pressure must be used to avoid damaging the gauge when thesteering 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 supplypressure during LOW PRESSURE STANDBY. The VIMS refers to this switch as the "lowsteering 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. TheVIMS refers to this switch as the "high steering pressure" switch.

Both steering pressure switches provide input signals to the Transmission/Chassis ECM. TheTransmission/Chassis ECM sends signals to the VIMS, which informs the operator of thecondition of the steering system. A steering system warning is only displayed if the groundspeed 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 andrelief valve manifold (2). The solenoid and relief valve manifold connects the steering pump tothe accumulator charging valve (3), the accumulators and the steering directional valve (4). Thesolenoid 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 connectedat the pressure tap (5).

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

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3

4

56

140

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

As pressure increases in the accumulators, pump supply pressure is sensed in the accumulatorcharging valve and on both ends of the flow compensator. With pressure on both ends of theflow compensator, the swashplate is kept at maximum angle by the force of the spring in thepump housing and pump discharge pressure on the swashplate piston. The pistons travel in andout of the barrel and maximum flow is provided through the outlet port. Since the pump isdriven 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 systemswith a margin pressure.


Pump Output

Load SensingPressure


To Accumulators

From Accumulators

Load SensingController

FlowCompensator

SwashplatePiston

ActuatorPiston

MAXIMUM FLOW789C STEERING PUMP

141

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

An orifice prevents supply pressure from filling the drained load sensing passage above the flowcompensator. Pump oil (at low pressure standby pressure) flows past the lower end of thedisplaced flow compensator spool to the actuator piston. The actuator piston has a larger surfacearea than the swashplate piston. The oil pressure at the actuator piston overcomes the springforce of the swashplate piston and moves the swashplate to destroke the pump. The pump isthen at a low flow, LOW PRESSURE STANDBY condition. Pump output pressure is equal tothe setting of the flow compensator. The LOW PRESSURE STANDBY setting must bebetween 2070 and 3600 kPa (300 and 525 psi).

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


Pump Output

Load SensingPressure

LOW PRESSURE STANDBY

To Accumulators

From Accumulators

Load SensingController

789C STEERING PUMP

FlowCompensator


SwashplatePiston

ActuatorPiston

When the pressure in the accumulators decreases to 16470 ± 350 kPa (2390 ± 50 psi), theaccumulator charging valve shifts (cut-in) and blocks the load sensing signal line pressure fromthe 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 tothe tank. Venting pressure from the actuator piston positions the spring biased swashplate tomaximum 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 thepressure tap on the bottom of the steering directional valve will indicate these steering systempressures. If pump pressure cycles in less than 25 seconds, leakage is in the system and must becorrected. 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 theframe 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 springforce 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 thepressure setting. Do not exceed 14 N•m (10 lb. ft.) torque on the adjustment screw whenmaking the adjustments. One turn of the adjustment screw changes the pressure approximately4000 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. Thepressure gauge will indicate these steering system pressures. Turn the adjusting screw until thecut-out pressure is correct.

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

NOTE: When testing or adjusting any steering system pressure settings, always allowthe 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 inaccuratereadings.

142


1 2

3

143

Pump pressure limiting (high pressure cutoff) is adjustable. To adjust the pump high pressurecutoff valve, turn the accumulator charging valve adjustment screw all the way in, or disconnectthe load sensing (LS) line (pump to accumulator charging valve) at the pump. Plug the line tothe accumulator charging valve and cap the fitting on the pump. Operate the engine at LOWIDLE, and check the pump (accumulator) pressure at the pressure tap below the steeringdirectional 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 theaccumulator 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 pumpwill stay at MINIMUM FLOW, and the steering system will take too long to recharge. The highpressure cutoff adjustment provides a back-up if the accumulator charging valve malfunctions.


High Pressure CutoffAdjustment Screw

To Tank

To Actuator Piston

From Pump Output Port

Low PressureStandby Adjustment Screw


FromAccumulator

Disconnect and Plug Linefor

High Pressure Cutoff Test

ToAccumulator

LOAD SENSING CONTROLLER

Pump LOW PRESSURE STANDBY is also adjustable. Connect a gauge to the low pressurestandby pressure tap (see Visual No. 138). With the signal line connected, operate the engine atLOW 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 andcounterclockwise to decrease the pressure until the pressure is between 2070 and 3600 kPa (300and 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 marginpressure 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 standbyreading measured on a truck is higher than the test stand margin pressure due toparasitic loads in the truck steering system.


On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid andrelief valve manifold. The solenoid and relief valve manifold connects the steering pump to theaccumulator charging valve, the accumulators and the steering directional valve. The solenoidand 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 thepump destrokes to LOW PRESSURE STANDBY.

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

The back-up relief valve (3) protects the system from pressure spikes if the pump cannotdestroke fast enough or limits the maximum pressure if the steering pump high pressure cutoffvalve 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 beconnected to the secondary steering connector (5) on the solenoid and relief valve manifold andto a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil tocharge 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 andrelief valve manifold. The solenoid and relief valve manifold connects the steering pump to theaccumulators and the HMU. The solenoid and relief valve manifold also provides a path todrain 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 accumulatorswhen the truck is not in operation.

The back-up relief valve (2) limits the maximum pressure if the steering pump compensatorvalve 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 beconnected to the secondary steering connector (4) on the solenoid and relief valve manifold andto a suction port on the hydraulic tank (see Visual No. 133). The APU will provide supply oil tocharge 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 thebottom 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 bleeddown 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 shutdowncontrol holds the solenoid open for 70 seconds.

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


Back-up Relief Valve

Bleed DownSolenoid

SOLENOID ANDRELIEF VALVE MANIFOLD

To / FromAccumulators

SupplyFrom Pump

To Tank

To SteeringControl Valve

The back-up relief valve protects the steering system if the steering pump malfunctions (fails todestroke). Pressure oil from the steering pump works against the end of the back-up relief valveand 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 theback-up relief valve can be changed by adjusting the spring force that keeps the relief valveseated (closed). To change the relief valve setting, remove the protective cap and turn theadjustment 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 amanual hydraulic pump at the location of the Auxiliary Power Unit (APU) connector andinstalling blocker plates to prevent oil from flowing to the accumulators. See the service manualfor more detailed information.

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


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

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

147


1

2

148

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

Pressure oil from the accumulators flows past the spring biased priority spool and is blocked bythe amplifier spool. The same pressure oil flows through an orifice to the right end of thepriority spool. The orifice stabilizes the flow to the priority spool and must be present to openand close the priority spool as the flow demand changes. The same pressure oil flows to theHMU. After all the passages fill with pressure oil, the priority spool shifts to the left, butremains 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 "thermalbleed" 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 heldin the center position by the centering springs.


Relief / MakeupValve

Left TurnCylinder Back Pressure

Valve

Left TurnPilot Oil

Amplifier Spool

Right TurnPilot Oil

Combiner / CheckSpool

LoadSensing Port

FromAccumulator

Priority Spool

STEERINGDIRECTIONAL VALVE

Right TurnCylinder


Hand Metering Unit Supplyand Thermal Bleed

NO TURN

To Tank

While the truck is traveling straight (no steer), any rolling resistance (opposition) acting on thesteering cylinders creates a pressure increase. The increased pressure acts on the relief/makeupvalve in that port. If the pressure increase exceeds 28000 ± 1000 kPa (4065 ± 150 psi), the reliefpoppet will open. A pressure drop occurs across the orifice. The pressure drop causes the dumpvalve 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 andreplenish 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 theother relief/makeup valve. A pressure difference of 48 kPa (7 psi) between the tank passage andthe low pressure cylinder port causes the makeup valve to open. The excess oil flows into thelow pressure cylinder port to prevent cavitation of the cylinder. The back pressure valve alsoprevents cavitation of the cylinders by providing a positive pressure of 170 kPa (25 psi) in thepassage behind the makeup valve. A pressure higher than 170 kPa (25 psi) will open the backpressure valve to the tank.

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

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

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


149

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

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

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


Amplifier Spool

BackPressure Valve

Left TurnPilot Oil

Right TurnPilot Oil

Combiner / Check

Spool

Load Sensing Port

FromAccumulator

Hand MeteringUnit Supply andThermal Bleed

Priority Spool

STEERINGDIRECTIONAL VALVE

RIGHT TURN


Left TurnCylinder

Right TurnCylinder

Relief/makeupValve

To Tank

Pilot oil also flows through a connecting pin hole and a stabilizing orifice to the left end of theamplifier spool and causes the amplifier spool to move to the right. Accumulator oil at thespring end (right end) of the amplifier spool flows through a mid-connecting pin to the left endof 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 theeight orifices. Pilot and accumulator oil combine. Oil flows across the directional spool (whichhas already shifted) for a RIGHT TURN.

The faster the steering wheel is turned, the farther the directional spool and the amplifier spoolare shifted. A higher flow rate is available, which causes the truck to turn faster. The ratio ofpilot and pump supply oil that combine is always the same because one orifice is dedicated topilot 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 thatsteering cylinder and oil line increases. Oil flow to the cylinder is reversed. This pressure spikeis felt in the amplifier spool. The combiner/check spool moves to the right and blocks the sevenpump supply oil orifices to the steering cylinders. The amplifier spool moves to the left andblocks the pilot oil orifice. Pilot oil flow to the steering cylinders stops. The pressure spike isnot felt at the HMU. If the pressure spike is large enough, the relief/makeup valve drains thepressure oil to the tank as previously described.


Shown is the solenoid and relief valve manifold (1) and the crossover relief valves (2) on the785C truck.

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

The crossover relief valve housing contains two pressure taps (3) where steering system pressurecan be measured. One tap shows pressure during a left turn and the other tap shows pressureduring 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 havestopped and the pressure will increase to the pump compensator valve setting. Check thesteering pressure while turning in both directions. The pump compensator valve setting shouldbe observed on the gauge in both directions. If the pressure readings are different, one of thecrossover relief valve settings is probably incorrect. A misadjusted valve must be removed andreadjusted on a test bench.

On the 785C, one pressure switch (4) monitors the condition of the steering system. The switchprovides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECMsends 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 steeringcylinders and in the lines between the steering cylinders and the HMU. The oil blockageprevents the front wheels from moving when the steering wheel is not turned. If pressure isapplied against the front wheels while the steering wheel is stationary, the pressure of the oilincreases in the head end of one cylinder and the rod end of the other cylinder. If the increase ofoil pressure exceeds 18270 kPa (2650 psi) at the affected crossover relief valve, the valve willopen. Oil from the high pressure ends of the steering cylinders then transfers to the low pressureends of the cylinders.


CrossoverRelief Valves

HandMetering Unit

785C CROSSOVER RELIEF SYSTEMEXTERNAL IMPACT

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

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

The 785C HMU is larger because oil flows directly from the HMU, through the crossover reliefvalve, to the steering cylinders. The capacity of the 785C HMU must be large enough to handlethe 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 signalline to the steering directional valve.

152


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

Inside each accumulator is a rubber bladder that is charged with nitrogen. The nitrogen chargeprovides energy for normal steering and secondary steering capability if steering pump flowstops.

To check the secondary steering system, the engine must be shut off with the manual engineshutdown 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 theaccumulators 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. Theswitch provides an input to the VIMS. The VIMS refers to this switch as the "high steeringpressure" switch.

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

153


WARNING

1

2

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

The steering accumulator bleed down solenoid is activated by the control when the key startswitch is moved to the OFF position. The bleed down solenoid shutdown control holds thesolenoid 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 theTransmission/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 ofthe SNUB position because a corresponding lever position is not provided. When the body isbeing lowered, just before the body contacts the frame, the Transmission/Chassis ECM signalsthe 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 factorywithout bodies installed are set at the Hoist Enable Status 2. The Hoist Enable Status 2 is a testmode only and will prevent the hoist cylinders from accidentally being activated. After the bodyis installed, change the Hoist Enable Status to 1 for the hoist system to function properly.


HOIST SYSTEM

789C

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. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andbody pads and not on the hoist cylinders. The hoist control valve will actually be in the SNUBposition.

If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is usedto 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, thelever 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 PWMsensor sends duty cycle input signals to the Transmission/Chassis ECM. Depending on theposition of the sensor and the corresponding duty cycle, one of the two solenoids located on thehoist valve is energized.

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

The hoist lever sensor also replaces the body raise switch (transmission neutralizer switch) thatwas 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. Tocheck the supply voltage of the sensor, connect a multimeter between Pins A and B of the sensorconnector. Set the meter to read "DC Volts."

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

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 bechecked with cold oil and the engine stopped. The level should again be checked with warm oiland the engine running.

The lower sight gauge is used when filling the hydraulic tank with the hoist cylinders in theRAISED 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 sightgauge 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 oilhydraulic tank. The hoist system pumps pull oil from the hydraulic tank through the suctionscreens (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 atthe top rear of the pump drive. Oil flows from the hoist pump through two screens to the hoistvalve. 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. Thebody position sensor rod must be disconnected from the body and the sensor must be rotated tothe RAISE position before the LOWER relief pressure can be tested.

In the HOLD, FLOAT, and SNUB positions, the gauge will show the brake cooling systempressure, which is a result of the restriction in the coolers, brakes, and hoses (normally muchlower than the actual oil cooler relief valve setting). The maximum pressure is limited by the oilcooler 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 hoistscreen bypass switches (2) provide input signals to the Transmission/Chassis ECM. TheTransmission/Chassis ECM sends signals to the VIMS, which informs the operator if the hoistscreens are restricted.

161


1 2

Oil flows from the hoist pump through two ports (1) (only one visible in this view) to the hoistcontrol 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 remainclosed until the pump supply pressure is higher than the pressure in the hoist cylinders. The loadcheck 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 RAISErelief valve (3) controls the pressure in the hoist system during RAISE. The LOWER reliefvalve (4) controls the pressure in the hoist system during LOWER. The relief valve housingmust 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 sideof 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 counterbalancevalve prevents cavitation of the cylinders when the body raises faster than the pumps can supplyoil to the cylinders (caused by a sudden shift of the load). The counterbalance valve signalpressure 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 limitsthe rear brake oil cooling pressure when the hoist valve is in the HOLD, FLOAT, or SNUBposition. 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 spoolinside 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 areused to drain the pilot oil from the ends of the directional spool, which then allows the spool tomove. 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 afrequency 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, theTransmission/Chassis ECM sends an output signal current between 0 and 1.9 amps to one of thesolenoids. The amount of current sent to the solenoid determines the amount of pilot oil that isdrained from the end of the directional spool and, therefore, the distance that the directionalspool travels toward the solenoid.

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


164

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

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

A gauge connected to the hoist system pressure taps while the hoist valve is in the HOLDposition will show the brake cooling system pressure, which is a result of the restriction in thecoolers, 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 oilcooler relief valve. The setting of the oil cooler relief valve is 790 kPa (115 psi).


To Hoist CylinderRod End

To Hoist CylinderHead End

To Rear Brake Oil Coolers

Rear BrakeOil Cooler

Relief Valve

Parking BrakeRelease Pressure

LowerSolenoid

RaiseSolenoid


PumpSupply Port

To Tank

Low PressureRelief Valve

High PressureRelief Valve

CounterbalanceValve

"C" SERIESHOIST CONTROL VALVE

HOLD

Dual StageRelief ValveSignal Stem

Rod EndVent Slot

Load CheckValve

Main ReliefDump Spool

165

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

When the directional spool is initially shifted, the two load check valves (one shown) remainclosed until the pump supply pressure is higher than the pressure in the hoist cylinders. The loadcheck 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 signalstem and the counterbalance valve. The dual stage relief valve signal stem moves down andblocks the supply pressure from opening the low pressure relief valve.


From Hoist CylinderRod End

To Hoist CylinderHead End

To Rear BrakeOil Coolers


Relief ValveTo Tank



CounterbalanceValve

RAISE

Rod EndVent Slot

Load CheckValve


LowerSolenoid


RaiseSolenoid


PumpSupply Port



On

The counterbalance valve is held open by the hoist cylinder raise pressure. Oil from the rod endof the hoist cylinders flows freely to the rear brake oil coolers. If the body raises faster than thepump can supply oil to the hoist cylinders (caused by a sudden shift of the load) and the raisepressure drops below 2275 kPa (330 psi), the counterbalance valve starts to close and restrictsthe flow of oil from the rod end of the hoist cylinders. Restricting the flow of oil from the rodend of the hoist cylinders will slow down the cylinders and prevent cavitation. Cavitation in thehoist cylinders can cause the body to drop suddenly when the hoist lever is moved from theRAISE 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. Whenthe high pressure relief valve opens, the dump spool moves to the left, and pump oil is directedto the rear brake oil coolers.

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


166

During RAISE, the counterbalance valve prevents the dump body from running ahead of thehoist pumps if the load shifts rapidly to the rear of the body and attempts to pull the hoistcylinders. Signal pressure from the head end of the hoist cylinders holds the counterbalancevalve open. Oil from the rod end of the hoist cylinders flows unrestricted through thecounterbalance 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 thecylinders to the tank.

If no head end signal pressure is present, rod end pressure can still open the counterbalancevalve. If the rod end pressure exceeds 6900 ± 690 kPa (1000 ± 100 psi) at the rod end pressurepiston, 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 pumpthrough a check valve to the rod end of the hoist cylinders.


RAISE

Head EndSignal Pressure

FromHoist Cylinder

Rod End

To Tank

LOWER AND FLOAT

ToHoist Cylinder

Rod End

FromPump

Check Valve

HOISTCOUNTERBALANCE

VALVE

Rod EndPressure

Piston

167

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

Supply oil from the pump flows past the directional spool, through the counterbalance valve, tothe 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 totheir retracted positions.

Just before the body contacts the frame, the body position sensor sends a signal to theTransmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUBposition, 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 dualstage relief valve signal stem allows supply pressure to be limited by the low pressure reliefvalve.



From Hoist CylinderHead End



Relief ValveTo Tank



CounterbalanceValve

Rod EndVent Slot

Load CheckValve

LowerSolenoid

RaiseSolenoid

LOWER (POWER DOWN)




PumpSupply Port



On

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 valveopens, 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 thehoist pump. Check the relief pressures with the hoist lever in the LOWER position and theengine at HIGH IDLE.

When the body is in the DOWN position, the hoist valve will be in the SNUB position. Thebody position sensor rod must be disconnected from the body, and the sensor must be rotated tothe 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 ispartially energized and drains part of the pilot oil pressure above the directional spool to thetank. The directional spool moves up. Because the pilot pressure is only partially drained, thedirectional spool does not move as far up as during LOWER.

Pump supply oil flows past the directional spool, through the counterbalance valve, to the rodend of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. Thedirectional valve is in a position that permits the pressure of the oil flowing to the rear brake oilcoolers 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. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andbody 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 theTransmission/Chassis ECM to move the valve spool to the SNUB position. In the SNUBposition, the valve spool moves slightly to restrict the flow of oil and lower the body gently.




Relief ValveTo Tank



CounterbalanceValve

FLOAT

Rod EndVent Slot

Load CheckValve

LowerSolenoid

RaiseSolenoid




PumpSupply Port



On


From Hoist CylinderHead End

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 canbe 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 hoistcylinders. Follow the same procedure used to lower the body with a dead engine, except keepthe hoist lever in RAISE after the 15 seconds interval.

NOTE: For more information on using the APU, refer to the Special Instructions "Using1U5000 Auxiliary Power Unit (APU)" (Form SEHS8715) and "Using the 1U5525Attachment 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 spoolinside the hoist valve. Two solenoid valves are used to drain the pilot oil from the ends of thedirectional spool. The solenoid valve on the left is energized in the RAISE position. Thesolenoid 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 throughthe 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 oilcooling 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 thehoist lever is held in the RAISE position, supply oil flows to the head end of the hoist cylindersand moves the two stage cylinders to their extended lengths. The oil from the rod end of thecylinders flows through the hoist valve to the rear brake oil cooling circuit.


��

��

��

��

��

�� !��"#

� ��

� ��

When the hoist lever is moved to the LOWER or FLOAT position and the cylinders areextended, supply oil enters the rod end of the hoist cylinders and lowers the second stage of thecylinders. The oil from the head end of the cylinders flows through the hoist valve to thehydraulic tank.


171

AIR SYSTEM AND BRAKES

Two separate brake systems are used on the "C" Series trucks. The two brake systems are: theparking/secondary brake system and the service/retarder brake system.

The parking/secondary brakes are spring engaged and hydraulically released. Theservice/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 compressorsupplies the air and fills two tanks. Air from the tanks provides energy to perform severalfunctions:

- Engine start-up- Service and retarder brake control- Secondary and parking brake control- Automatic lubrication injection (grease)- Horn, air seat, and cab clean-out


AIR SYSTEM AND BRAKES

789C

Shown is a cutaway illustration of an oil cooled brake assembly. The brakes areenvironmentally sealed and adjustment free. Oil continually flows through the brake discs forcooling. Duo-Cone seals prevent the cooling oil from leaking to the ground or transferring intothe axle housing. The wheel bearing adjustment must be maintained to keep the Duo-Cone sealsfrom leaking.

The smaller piston (yellow) is used to ENGAGE the secondary and parking brakes. The parkingbrakes are spring ENGAGED and hydraulically RELEASED.

The larger piston (purple) is used to ENGAGE the retarder/service brakes. The retarder/servicebrakes 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 systempressure 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. Turnthe 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 beenincreased from a two-cylinder compressor to a four-cylinder compressor. To handle theincreased air flow, two larger air dryers are used, and the hoses and tubing have also beenincreased in size.

To test the air compressor efficiency, lower the air system pressure to 480 kPa (70 psi). Start theengine 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) to690 kPa (100 psi). The time to raise the pressure should be 50 seconds or less. If the timerecorded is greater than 50 seconds, check for leaks or a restriction in the system. If no leaks orrestrictions 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 leftfront 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 thedesiccant 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 of830 kPa (120 psi), the governor sends an air pressure signal to the purge valve in the bottom ofthe dryers. The purge valve opens and air pressure that is trapped in the air dryers is exhaustedthrough 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 compressorgovernor malfunctions.

A heating element in the bottom of the dryers prevents moisture in the dryers from freezing incold weather.

174


1

2

Air flows through the air dryers and fills two tanks. The service/retarder brake tank (1) islocated 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 brakesystem.

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. Thisrelief valve protects the air system when the air dryers have exhausted and the ball check valvesin the air dryer outlet ports close. The check valves separate the air system from the air dryerrelief valves.

175


1

2

Located behind the operator’s station is a pressure protection valve (1). Supply air flows fromthe large service/retarder brake tank, through the pressure protection valve, to the secondary airsystem and accessories. The pressure protection valve opens at 550 kPa (80 psi) and closes at482 kPa (70 psi). If the secondary air lines or an accessory circuit fails, the pressure protectionvalve 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 LOWIDLE, press the horn button. Record the air pressure when the horn sounds. This pressurereading is the open setting of the pressure protection valve. Slowly drain the air pressure andrecord the air pressure when the horn turns off. This pressure reading is the setting of thepressure protection valve when it closes.

The air system pressure sensor (2) provides an input signal to the Brake ECM. The Brake ECMsends 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, theparking/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 thesolenoid ten minutes after the machine is started. The VIMS keeps the solenoid ENERGIZEDfor 75 seconds and then DE-ENERGIZES it. Every 60 minutes thereafter, the VIMSENERGIZES the solenoid for 75 seconds until the machine is stopped (turned off). Thesesettings 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 islocated on the right side of the cab. Moisture should be drained from the tank daily through thedrain 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 theair 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 pressurein the service/retarder tank reaches 550 kPa (80 psi), the pressure protection valve allows air toflow 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 ofthe tank occurs.


Air Compressorand Governor

AirDryers

PressureProtection

Valve

Service / RetarderBrake Tank

Parking / SecondaryBrake Tank

Low AirSensorTo Auto Lube Solenoid

To Horn / Seat / Clean-out

To Air StartSolenoid

789C AIR CHARGING SYSTEM

RemoteSupply

Brake Systems

The manual retarder valve (arrow) is controlled by the retarder lever in the cab. Normally, theretarder valve blocks air flow to the service brake relay valve near the brake master cylindersand 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 frontbrake oil cooler diverter valve [maximum pressure is approximately 550 kPa (80 psi)]. Theretarder lever is used to modulate the service brake engagement by metering the amount of airflow to the service brake relay valve.

The retarder engages the same brakes as the service brake pedal (see Visual No. 43), but is easierto control for brake modulation.

The retarder system allows the machine to maintain a constant speed on long downgrades. Theretarder will not apply all of the normal braking capacity.

NOTICE

Do 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 servicebrake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve (2) issupplied from the manifold (3).

When the service brakes are engaged, air flows from the service brake valve to the service brakerelay 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 brakemodulation as precisely as the retarder.

Air from the service brake valve and the manual retarder valve flows through the double checkvalve (4) to the service brake relay valve and through the double check valve (5) to the frontbrake oil cooler diverter valve. If the manual retarder and the service brakes are engaged at thesame time, air from the system with the highest pressure will flow through the double checkvalves 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 retarderswitch (7). The retarder switch turns on the amber retarder lamp on the dash in the operator’sstation 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 locatednear the brake master cylinders. Air also flows from the ARC valve through the double checkvalve (6), to the retarder switch (7), and through double check valve (5) to the front brake oilcooler diverter valve.

The brake light switch and the service/retarder brake switch (see Visual No. 128) are located inthe supply line to the front brake oil cooler diverter valve (see Visual No. 102). The servicebrake valve, the manual retarder valve, and the Automatic Retarder Control (ARC) valve sendair 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 signalport of an inverter valve (see next visual). The inverter valve then blocks the flow of air fromthe 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 todrain the oil from the parking brakes, which allows the springs in the parking brake toENGAGE the brakes. The secondary brake valve can be used to modulate parking brakeengagement 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 theflow of air to the brake release valve, but the parking brake air valve does not modulate theparking brake application.

The parking/secondary brake switch (see Visual No. 128) is located in the supply line to thebrake release valve. The secondary brake valve and the parking brake air valve send air to thisswitch when engaged.

INSTRUCTOR NOTE: The ARC system will be discussed in more detail later in thispresentation.


When the secondary brakes are engaged, air flows from the secondary brake valve to the signalport (1) of the inverter valve (2). The inverter valve then blocks the flow of air from thesecondary brake tank to the brake release valve.

Blocking the air from the brake release valve positions the spool in the brake release valve todrain the oil from the parking brakes, which allows the springs in the parking brake to ENGAGEthe brakes.

182


1

2

Oil from the parking brake release pump (see Visual No. 98) flows through the parking brakerelease filter (see Visual No. 101) to the brake release valve (1) located inside the left frame nearthe torque converter. Oil flows from the parking brake release valve to the parking brake pistonin the brakes when the parking brakes are released.

Supply air from the parking brake air valve in the cab or the secondary brake valve flowsthrough the small hose (2) to an air chamber in the brake release valve. The brake release valvecontains an air piston that moves a spool. The spool either directs oil to RELEASE the parkingbrakes or drains oil to ENGAGE the parking brakes. A relief valve (3) in the brake release valvelimits 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 oilmakeup tank.

To release the parking brakes for service work or towing, the electric motor that turns the towingpump (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 pumppressure 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 brakerelease filter, to the parking brake release valve. If air pressure is present from the parking brakeair 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 forreleasing the brakes, torque converter lockup, and for the pilot oil to shift the hoist valve. Thesetting 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 towingsystem is activated.

Oil flow from the parking brake release pump has stopped. The towing motor is energized, andair pressure is present above the parking brake release valve piston. The air pressure moves thespool 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. Thecheck valve to the right of the parking brake release filter blocks the oil from the towing pumpfrom flowing to the parking brake release pump.


Parking BrakeRelease Valve

Towing Pumpand Motor

ParkingBrake

ReleasePump

Towing PumpRelief Valve

CheckValve

To HoistPilot

System

ReliefValve

ToTC Lockup

ValveParkingBrake

ReleaseFilter

From Cab Secondaryor Parking Brake Valve

TOWING SYSTEM

During towing, the parking brake release pressure is limited by a relief valve in the towingpump. When the relief valve opens, oil transfers from the pressure side to the suction side of thetowing 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 towingpump during normal operation.

To check the brake release system used for towing, connect a gauge to the parking brake releasepressure tap on the rear axle (see Visual No. 189). Use a long gauge hose so the gauge can beheld in the cab. With the parking brake air valve in the RELEASE position and the key startswitch in the ON position, energize the parking brake release switch used for towing (on thedash). The parking brake release pressure should increase to 4480 kPa (650 psi). Turn off theswitch when the pressure stops increasing.

The parking brake release pressure must increase to a minimum of 3790 kPa (550 psi). Theparking 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 releasepressure decreases below this level or the brakes will drag. The parking brakes are fullyreleased between 3445 and 3860 kPa (500 and 560 psi).

NOTE: A minimum of 550 kPa (80 psi) air pressure must be available at the parkingbrake release valve to ensure full release of the brakes for towing.

NOTICE

Activate the brake release switch only when additional pressure is required to release thebrakes. Leaving the brake release (towing) motor energized continuously will drain thebatteries.

The parking brake release pressure setting must not exceed 5445 kPa (790 psi). Exceedingthis pressure can cause internal damage to the brake assembly.


185

Shown is the parking/secondary brake hydraulic and air system with the secondary brakesRELEASED and the parking brakes ENGAGED.

Supply air from the parking/secondary brake air tank flows to the secondary brake valve and isblocked from flowing to the inverter valve signal port. Supply air is allowed to flow through theinverter 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 fromthe parking brake release pump is blocked by the spool. Oil from the parking brake is open todrain through the parking brake release valve, which allows the springs in the parking brake toENGAGE the brakes.

A parking/secondary brake switch is located in the air line between the parking brake valve andthe parking brake release valve. The switch provides an input signal to theTransmission/Chassis ECM. When the parking or secondary brakes are ENGAGED, the switchsignals the Transmission/Chassis ECM to allow rapid downshifts.


ParkingBrakeValve

SecondaryBrakeValve

ParkingBrake

ReleaseValve

PARKING / SECONDARY BRAKES PARKING BRAKES ENGAGED

To TC Lockup Valveand Hoist

Pilot System

ParkingBrake

ReleasePump

SECONDARY BRAKES RELEASED

Parking / SecondaryBrake Tank

Parking /Secondary

BrakeSwitch

InverterValve

The front service brake relay valve (1) receives metered air from only the service brake valve orthe 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 opensand metered air flows from the service brake tank, through the double check valves (3), to thethree brake cylinders (4). The brake relay valves reduce the time required to engage and releasethe brakes. The double check valves (3) are used to separate the service and manual retarderbrakes from the ARC brake system.

When the ARC brake system is ENGAGED, the rear relay valve opens and metered air flowsfrom 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 airpressure in the service brake air system if the ARC relay valve fails. The protection valve opensto send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreasesbelow 310 kPa (45 psi).

The brake cylinders operate by air-over-oil. When the metered air enters the brake cylinders, apiston moves down and pressurizes the oil in the bottom of the cylinders. One brake cylindersupplies oil to the front brakes through the slack adjuster (6). Two brake cylinders supply oil tothe 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 tocompensate for the wear. The brake makeup oil tank (1) supplies makeup oil for the brakecylinders. 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 cancause 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 atHIGH 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 oildownstream from the cylinders occurs, the piston in the cylinder will overstroke and cause anindicator rod to extend and open the brake overstroke switch (3). The switch provides an inputsignal to the Brake ECM. The Brake ECM sends the signal to the VIMS, which informs theoperator of the condition of the service/retarder brake oil circuit. If an overstroke conditionoccurs, 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 slackadjuster.

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 theslack adjuster. When the service brakes are ENGAGED, if the air pressure in the brake cylinderis 690 kPa (100 psi), the oil pressure measured at the slack adjuster should be approximately4560 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 thebreathers. Oil leaking from the breathers is an indication that the oil piston seals in the brakecylinder need replacement. Air flow from the breathers during a brake application is anindication 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 pistonand 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 thecylinder will overstroke, which causes the indicator rod to extend and open the brake overstrokeswitch. If an overstroke condition occurs, the problem must be repaired and the indicator rodpushed in to end the warning.

When the air pressure is removed from behind the air piston, the spring moves the air piston andthe attached rod opens the valve in the oil piston. Any makeup oil that is needed flows into thepassage at the top of the oil chamber, through the valve, and into the oil chamber at the right ofthe oil piston.


AirPiston

RodSpring

Indicator Rod

AirInlet

BRAKE CYLINDERBRAKES ENGAGED

Valve

OilPiston

FromMakeup

Tank

ToSlack

Adjuster

BreatherPort

The truck is equipped with two slack adjusters--one for the front brakes and one for the rearbrakes. The slack adjuster (1) shown is for the rear brakes. The slack adjusters compensate forbrake disc wear by allowing a small volume of oil to flow through the slack adjuster and remainbetween the slack adjuster and the brake piston under low pressure. The slack adjustersmaintain 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 slackadjusters.

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 locatedon each wheel.

189


1

2 33

190

This visual shows sectional views of the slack adjuster when the brakes are RELEASED andENGAGED.

When the brakes are ENGAGED, oil from the brake cylinders enters the slack adjusters and thetwo large pistons move outward. Each large piston supplies oil to one wheel brake. The largepistons 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 slackadjusters reach the end of their stroke. As the brake discs wear, the service brake piston willtravel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther, thelarge piston in the slack adjuster moves farther out and contacts the end cover. The pressure inthe slack adjuster increases until the small piston moves and allows makeup oil from the brakecylinders to flow to the service brake piston.

When the brakes are RELEASED, the springs in the service brakes push the service brakepistons away from the brake discs. The oil from the service brake pistons pushes the largepistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used toENGAGE the brakes is replenished at the brake cylinders from the makeup tank.


Oil FlowTo BrakeCylinder

Oil FlowFrom Brake

Cylinder

FromWheelBrakes

ToWheelBrakes

ToWheelBrakes

BRAKES ENGAGEDBRAKES RELEASED

Large PistonSmall Piston

FromWheelBrakes

BRAKE SLACK ADJUSTER

SERV1706-01 - 230 - Text Reference7/05SERV1706-01 - 230 - Text Reference7/05

The spring behind the large piston causes some oil pressure to be felt on the service brake pistonwhen the brakes are RELEASED. Keeping some pressure on the brake piston provides rapidbrake engagement with a minimum amount of brake cylinder piston travel.

The slack adjusters can be checked for correct operation by opening the service brake bleedscrew with the brakes RELEASED. A small amount of oil should flow from the bleed screwwhen the screw is opened. The small flow of oil verifies that the spring behind the large pistonin 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 tapon top of the slack adjuster and another gauge at the service brake bleed screw location. Withsystem air pressure at maximum and the service brake pedal depressed, the pressure reading onboth gauges should be approximately the same.

When the brakes are RELEASED, the pressure at the slack adjuster should return to zero. Thepressure at the service brake bleed screw location should return to the residual pressure held onthe 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 alsoindicate a failed slack adjuster or warped brake discs. To check for warped brake discs, rotatethe wheel to see if the pressure fluctuates. If the pressure fluctuates while rotating the wheel, thebrake discs are probably warped and should be replaced.

To check for brake cooling oil leakage, block the brake cooling ports and pressurize each brakeassembly to a maximum of 138 kPa (20 psi). Close off the air supply source and observe thepressure trapped in the brake assembly for five minutes. The trapped pressure should notdecrease.

191

This schematic shows the flow of air through the service/retarder brake air system when theretarder (manual and automatic) is RELEASED, and the service brakes are ENGAGED. Supplyair pressure flows from the large service brake air tank to the relay valves and the service brakevalve, manual retarder valve, and the ARC valve.

The manual retarder valve and the ARC solenoids block the flow of air. The service brake valveallows air to flow to two double check valves that block the passages to the manual retarder andARC valves. Air pressure from the service brake valve flows through the double check valvesto 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 tankto the brake cylinders. The relay valves reduce the time required to engage and release thebrakes. A pair of double check valves above the brake cylinders prevent the flow of servicebrake air to the ARC relay valve.

Air from the service brake valve also flows to the brake light switch and the service/retarderbrake switch. Depressing the service brake pedal turns ON the brake lights and changes thetransmission shift points and anti-hunt timer.


ServiceRelayValve

ServiceBrake Valve

RetarderValve

Brake Cylinders

ARCValve

SERVICE / RETARDER BRAKE AIR SYSTEMSERVICE BRAKES ENGAGED

ARCRelayValve

BrakeLightand

Service /RetarderSwitch

RetarderSwitch

Front Brake CoolerDiverter Valve

PressureProtection

Valve

When the manual retarder lever is moved, air flows through three double check valves thatblock the passages to the service brake valve and the ARC valve. Air pressure from the manualretarder brake valve flows through the double check valves to the service brake relay valve andthe front brake oil cooler diverter valve.

Air from the manual retarder brake valve also flows to the retarder switch, the brake lightswitch, and the service/retarder brake switch. Engaging the manual retarder turns ON theretarder dash lamp, the brake lights, and changes the transmission shift points and anti-hunttimer.

When the ARC is activated, air flows through two double check valves that block the passagesto the service brake valve and the manual retarder brake valve. Air pressure from the ARCvalve 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 flowsfrom the service brake tank, through a pressure protection valve and the double check valves, tothe three brake cylinders. The pressure protection valve prevents a total loss of air pressure inthe service brake air system if the ARC relay valve fails. The protection valve opens to sendflow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below310 kPa (45 psi).

Air from the ARC valve also flows to the retarder switch, the brake light switch, and theservice/retarder brake switch. Engaging the ARC turns ON the retarder dash lamp, the brakelights, 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 pumpsections provide oil for rear brake cooling: the two-sections of the hoist pump and the fourthsection 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. Allthe 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 andFLOAT positions, oil from the pump flows through the hoist valve to the rear brake coolingsystem.

Oil flows from the fourth section of the torque converter pump, joins with the oil from the hoistvalve, and flows to the rear brake oil coolers.

Oil from all three pump sections combines and flows through the screens and rear brake oilcoolers located on the right side of the engine. The rear brake oil coolers are cooled by theengine jacket water cooling system. From the coolers, oil flows through the brakes and returnsto the hydraulic tank.


789C BRAKECOOLING SYSTEM

FrontBrakes

TorqueConverterCharging

Filter


Parking BrakeRelease Valve

DiverterValve

ConverterOutletFilter

ParkingBrakeFilter

Rear BrakeOil Coolers

Rear Brakes

OutletRelief Valve

InletRelief Valve

Hoist Pump

HoistScreens

HoistValve

The pressure in the rear brake cooling system is controlled by the oil cooler relief valve locatedin 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 divertervalve.

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 torqueconverter and shift the directional spool in the hoist valve. These functions require minimal oilflow. Most of the oil from the brake release pump flows through the brake release valve andjoins 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 valveallows brake cooling oil to flow through the front brake oil cooler to the front brakes. When thebrakes are RELEASED, the oil bypasses the cooler and flows directly to the brakes. The frontbrake oil cooler is cooled by the engine aftercooler cooling system. The aftercooler coolingsystem does not have temperature regulators (thermostats) in the circuit.

Normally, front brake cooling oil is diverted around the cooler and goes directly to the frontbrakes. Diverting oil around the cooler provides lower temperature aftercooler air during highpower 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 785Ctruck does not have a fourth section on the torque converter pump for rear brake cooling. Theparking brake release pump sends oil to the rear brake cooling system, not to the front brakecooling system.


Shown is the left rear brake housing on a 789C truck. Brake cooling oil pressure can be tested atthe two taps (arrow) located in the brake cooling oil tubes. One tap is located on the brakecooling inlet tube and another tap is located on the brake cooling outlet tube. The pressuremeasured at the brake inlet tube (from the oil coolers) will always be higher than the pressuremeasured at the brake outlet tube.

With the brake cooling oil temperature between 79 to 93°C (175 to 200°F), the pressuremeasured 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 operatorinformed of the brake cooling oil temperature.

The most common cause of high brake cooling oil temperature is operating a truck in a gear thatis too high for the grade and not maintaining sufficient engine speed. Engine speed should bekept at approximately 1900 rpm during long downhill hauls.

Also, make sure the pistons in the slack adjuster are not stuck and retaining too much pressureon 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 boththe Automatic Retarder Control (ARC) and the Traction Control System (TCS).

The Automatic Retarder Control (ARC) and the Traction Control System (TCS) control modulesare replaced with one Brake ECM. The Brake ECM controls both the ARC and the TCSfunctions. The TCS is now on the CAT Data Link, and the Electronic Technician (ET) servicetool can be used to diagnose the TCS.

The Brake ECM receives information from various input components such as the Engine OutputSpeed (EOS) sensor, retarder pressure switch, left and right wheel speed sensors, and the TCStest switch.

Based on the input information, the Brake ECM determines whether the service/retarder brakesshould 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.


Proportional(Servo) Solenoid

TCSEngaged Lamp TCS Selector Solenoid

Left and Right

ARC SupplySolenoid

Right Wheel Speed Sensor

INPUT COMPONENTS

OUTPUT COMPONENTS

Engine OutputSpeed Sensor

Transmission/chassis ECMEngine ECM

Service Tool CAT DATA LINK

ARC ControlSolenoid

Left Wheel Speed Sensor

Arc On / OffSwitch

On Input

Off Input

RetarderEngaged LampAuto Retarder

Pressure Switch

RetarderPressure Switch

TCS TestSwitch

ARC

TCS

ARC

TCS

Shift LeverSwitch

Actual GearSwitch

Parking / SecondaryBrake Switch

Transmission OutputSpeed Sensor

Service/retarderBrake Switch

ThrottleSensor

EngineSpeed/timing

Sensor

BRAKE ELECTRONIC CONTROL SYSTEM

VIMS

Brake OverstrokeSwitch

DifferentialOil Level

DifferentialFilter

Parking Brake Filter

Differential Fan Relay

Left BrakeReleasePressure

Right BrakeRelease Pressure

Differential OilTemp Sensor

Brake Air Pressure

DifferentialPressure

Output components include the ARC supply and control solenoids, the retarder ENGAGEDlamp, the TCS selector and proportional solenoids, and the TCS ENGAGED lamp.

The Brake ECM also provides the service technician with enhanced diagnostic capabilitiesthrough the use of onboard memory, which stores possible diagnostic codes for retrieval at thetime 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. Communicationbetween 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 ECMdoes 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 ControlAnalyzer 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 ECMdoes not have fittings for cooling fluid. Also, the Brake ECM has no access plate for apersonality 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 engagesthe service/retarder brakes. If the ON/OFF switch is moved to the ON position, the ARC will beactivated if the throttle pedal is not depressed and the parking/ secondary brakes areRELEASED. The ARC system is disabled when the throttle is depressed or when theparking/secondary brakes are ENGAGED.

The ARC is not connected to the service brakes and the manual retarder. When the ARC isENGAGED, air flows from the ARC valve to a separate relay valve located near the brakemaster cylinders (see Visual No. 182).

The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (enginespeed setting is programmable). When the ARC initially takes control of retarding, the enginespeed may oscillate out of the ± 50 rpm target, but the engine speed should stabilize within a fewseconds.


AutomaticRetarder

Valve

SupplySolenoid

ControlSolenoid

Auto RetarderPressure Switch

Vent

RetarderEngaged

Lamp

CAT Data Link

Arc On / OffSwitch

On Input

Off Input

Air FromService Brake

Reservoir

ServiceBrakeValve

ManualRetarder

Valve

RetarderPressureSwitch

To Service /Retarder Brake

Relay Valve

Vent

Engine SpeedSensor

To ARCRelay Valve

Brake ECM(ARC / TCS)


Engine ECMService Tool

VIMS

AUTOMATIC RETARDER CONTROL

For proper operation of the ARC, the operator needs only to activate the control with the ARCON/OFF switch and select the correct gear for the grade, load, and ground conditions. TheARC 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 exceeds1900 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 isreached, the ARC will engage the brakes, even if the ARC ON/OFF switch is in the OFFposition 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 theengine speed continues to increase, the Transmission/Chassis ECM will either upshift (one gearonly above shift lever position) or unlock the torque converter (if the shift lever is in the top gearposition) at 2300 rpm.

The ARC also provides service personnel with enhanced diagnostic capabilities through the useof onboard memory, which stores possible faults, solenoid cycle counts and other serviceinformation 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 speedcontrol setting.

The Auto Retarder Control receives signals from several switches and sensors. The controlanalyzes the various input signals and sends signals to the output components. The outputcomponents are two solenoids and a lamp.

NOTE: The ARC ON/OFF switch must be in the OFF position to run the ARCdiagnostic test with ET.

INSTRUCTOR NOTE: For more detailed information about the Automatic RetarderControl (ARC) system, refer to the Service Manual Module "Off-Highway Truck/TractorsBrake Electronic Control System" (Form SENR1503).


Shown is the location of the Engine Output Speed (EOS) sensor (1) that provides the primaryinput signal used by the ARC. The engine speed information is the main parameter that theBrake ECM uses to control retarding. The engine speed sensor is a frequency sensor thatgenerates an AC signal from the passing flywheel gear teeth.

The EOS sensor also provides an input signal to the Transmission/Chassis ECM forTransmission Output Speed (TOS) ratification and lockup clutch shift time. TheTransmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signalto 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 fromthe TOS and the ratio for the current transmission gear. If the speeds do not agree, thetransmission will not downshift. If EOS is less than 1000 rpm the lockup clutch will release. IfEOS exceeds 2300 rpm the lockup clutch will release. If EOS exceeds 2500 rpm thetransmission 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 theBrake ECM receives an input signal from the engine speed/timing sensor, but not the EOSsensor, the Brake ECM will log an engine speed fault. The ARC will not function without anengine speed signal from EOS sensor (1).

197


1

2

NOTE: The 8T5200 Signal Generator/Counter Group can be connected to the enginespeed sensor wiring harness and be used to simulate engine speed for diagnosticpurposes. A 196-1900 adapter is required to increase the frequency potential from thesignal generator when connecting to the ECM's used on these trucks. To connect the8T5201 Signal Generator to the engine speed sensor wiring harness, fabricate jumperwires and connect the 8T5198 Adapter Cable (part of the 8T5200 SignalGenerator/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 signalsthe Brake ECM when manual or automatic retarder air pressure is present. The switch isnormally 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 theautomatic retarder valve (3) is functioning. The auto retarder pressure switch is located in frontof the cab in the output port of the automatic retarder valve. The switch is normally closed andopens only when the auto retarder is engaged.

A fault is recorded when the Brake ECM detects the presence of auto retarder pressure (switchopen) 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 automaticretarder 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 reducedspeed 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 toground, 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 airpressure is allowed to the brakes. Voltage to the control solenoid increases proportionally fromzero 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, shortedto ground, or shorted to battery.

Normal resistance through the supply and control solenoids is 31 Ohms. An excess resistance ofapproximately 40 Ohms will prevent the valves from opening and will cause a supply or controlvalve fault to be logged. Therefore, a measurement of approximately 71 Ohms or more willshow 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 valvehas malfunctioned.


199

Hydraulic Automatic Retarder Control (ARC)

Signal air from the primary air tank flows to the service brake valve and the retarder valve. Ashuttle valve, after these valves, then sends the highest signal pressure to the service brake relayvalve. The service brake relay valve opens and actuates the brake cylinders with a greatervolume of air from the primary air tank.

An addition to the air system is the front brake cooling oil diverter solenoid. Air is supplied tothis valve from a smaller secondary air tank behind the cab. The Brake ECM energizes thisvalve when the service brakes are applied. When the Brake ECM energizes this solenoid, signalair is sent to the diverter valve for the front brake cooling oil. Brake cooling oil is then sentthrough the cooler for front brake cooling oil.


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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 continuesfrom the pump, through a check valve to the ARC valve. The ARC valve modulates the amountof 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 valvebetween the ARC system and brake cylinders separates these two systems. Whichever systemhas the greatest pressure, that system will control the service brakes.


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The hydraulic ARC valve (arrow) is located on the left frame rail near the rear differential. Thisvalve contains a supply solenoid valve and a control solenoid valve. A purge solenoid valve islocated on the bottom of the ARC valve. The ARC accumulator is located to the right of theARC valve.

NOTE: The hydraulic ARC valve performs the same functions as the previous aircontrolled 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 entersthe 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 samepressure as the parking brake release system pressure. Hydraulic flow is also routed through thesupply solenoid valve to apply pilot pressure to the left end of the ARC spool. This pressurewill keep the ARC spool in the blocked position.


ENGINE ON / ARC OFF

ControlSolenoid

Valve

To Tank

Supply SolenoidValve

PurgeSolenoid

Valve

Check Valve

Pump

Accumulator

Spool

ToServiceBrakes

203

The Brake ECM supplies current to the supply solenoid. The supply solenoid valve sends pilotoil to the right end of the ARC spool. This pilot oil shifts the ARC spool to the left opening theleft side of the ARC spool to tank. At the same time, pump supply oil is directed to the right sideof 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 currentwill modulate the spool within the proportional valve. The level of current is dependent on thebrake 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 thechamber 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 tomaintain the correct brake pressure, the Brake ECM will vary the current to the control solenoidto open and close the oil drain port.


ENGINE ON / ARC ON

ControlSolenoid

Valve

To Tank


PurgeSolenoid

Valve

Check Valve

Pump

Accumulator

Spool

ToServiceBrakes

ON

ON

204

No current is supplied from the Brake ECM to the supply solenoid. The supply solenoid valvedirects any pressurized oil acting on the ARC spool to flow to the tank. Current is supplied fromthe Steering Bleed Control to the purge solenoid valve for approximately 70 seconds. Thisallows the pressure within the accumulator to drain from the accumulator back to the tank.


ENGINE OFF / ARC OFF

ControlSolenoid

Valve

To Tank


PurgeSolenoid

Valve

Check Valve

Pump

Accumulator

Spool

ToServiceBrakes

ON

205

The introduction of the hydraulic ARC control valve has required a number of additionalcomponent changes. The basic function of the new system remains the same as the previoussystem. The Engine ECM, the Transmission/Chassis ECM, the Vital Information ManagementSystem (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.


ARCValve

SupplySolenoidPurge

Solenoid

Control Solenoid

ARC Spool

RetarderEngaged LampCAT Data Link

ARC On / OffSwitch

On Input

Off Input

Engine SpeedSensor


Service ToolConnector

AUTOMATIC RETARDER CONTROL

Front BrakeCooling Diverter

Solenoid

Parking BrakeRelease Pump

To Tank

ServiceBrakes

ARC ENGAGED

Steering BleedControl

The steering bleed down control (1) is located in the compartment behind the cab. While thesteering bleed control is not a new component, the control serves an additional function. Thesteering 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 willenergize the purge solenoid for a period of approximately 70 seconds to purge the ARCaccumulator.

206


One of the new components, located in the compartment behind the cab, is the front brakecooling diverter solenoid (arrow). When the ARC is engaged, the Brake ECM energizes thissolenoid to send an air signal to shift the brake cooling oil diverter valve. This will route thebrake cooling oil through the front brake oil cooler for increased cooling. Normally the brakecooling oil is routed around the front brake oil cooler. This is a 24 V normally closed solenoidvalve.

207


Shown is the location of the Engine Output Speed (EOS) sensor that provides the primary inputsignal used by the ARC. The EOS sensor is a passive (two wire) sensor and is located on top ofthe flywheel housing. The engine speed information is the main parameter that the Brake ECMuses to control retarding. The engine speed sensor is a frequency sensor that generates an ACsignal from the passing flywheel gear teeth.

The EOS sensor also provides an input signal to the Transmission/Chassis ECM forTransmission Output Speed (TOS) ratification and lockup clutch shift time. TheTransmission/Chassis ECM uses the EOS signal and the Converter Output Speed (COS) signalto 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 fromthe TOS and the ratio for the current transmission gear. If the speeds do not agree, thetransmission 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 thetransmission 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 speedsensor is located near the rear of the left camshaft. If the Brake ECM receives an input signalfrom the engine speed/timing sensor, but not the EOS sensor, the Brake ECM will log an enginespeed 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 andhydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tirewith better underfoot conditions to receive an increased amount of torque. The system iscontrolled 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 BrakeECM sends a signal to the selector and proportional valves which ENGAGE the brake of theaffected wheel. When the condition has improved and the ratio between the right and left axlesreturns 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). Theoperation 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 cancommunicate with the TCS.



ProportionalSolenoid

TCSEngaged

Lamp

TCS SelectorSolenoid

Left and Right

Right WheelSpeed Sensor

Left WheelSpeed Sensor

TCS TestSwitch

ElectronicService Tool

CAT Data Link

Service / RetarderBrake Switch

TransmissionOutput Speed Sensor

+ 10V toWheel Sensors

TRACTION CONTROL SYSTEM

A service/retarder brake switch (see Visual No. 128) provides an input signal to the TCSthrough 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 diagnostictest. When the TCS test switch and the retarder lever are ENGAGED simultaneously, theTCS will engage each rear brake independently. Install two pressure gauges on the TCSvalve, and observe the pressure readings during the test cycle. The left brake pressure willdecrease and increase. After a short pause, the right brake pressure will decrease andincrease. The test will repeat as long as the TCS test switch and the retarder lever areENGAGED.

The TCS valve has a left and right brake release pressure sensor. A laptop computer with theET software installed can also be used to view the left and right parking brake pressures duringthe test discussed above in function No. 2. When the proportional solenoid is ENERGIZED, ETwill 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 BrakeElectronic Control System" (Form SENR1503).


Shown is the right rear wheel speed sensor (arrow). The TCS monitors the drive wheels throughthree 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 speedof the machine and provides input signals to the TCS through the CAT Data Link. The TCSuses 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. Twosolenoids are mounted on the valve.

Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and selecteither the left or right parking brake. If the selector valve shifts to the left parking brakehydraulic circuit, the control oil is drained. The left reducing spool of the control valve can thenshift and engage the parking brake.

The Brake ECM energizes the selector solenoid valve with + Battery voltage (24 Volts). Normalresistance through the selector solenoid is between 18 and 45 Ohms.

The proportional solenoid valve (2) controls the volume of oil being drained from the selectedparking 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) fromthe 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 isbetween 12 and 22 Ohms.

The pressure taps (3) or pressure sensors (4) can be used to check the left and right brake releasepressures when performing diagnostic tests on the TCS. The pressure at the taps in the TCSvalve will be slightly less than the brake release pressure measured at the wheels. The pressuresensors 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 theflow is divided. One line from the filter directs oil to the parking brake release valve. Theother 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 theleft and unseat the drain ball check valve. Opening the drain ball check valve opens a drainpassage to the hydraulic tank.


ParkingBrakeValve

TransmissionSpeed Sensor


SelectorSolenoid


Screen

Orifice

LeftDrive Axle

RightDrive Axle

TRACTION CONTROL SYSTEM (TCS)ENGINE RUNNING/BRAKES RELEASED

Ball Check

OutputSignals

InputSignals

Tcs EngagedLamp

TestSwitch

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 fromthe sensors indicate that the left wheel is spinning 60% faster than the right wheel, the followingsequence of events occurs:

- The Brake ECM sends a signal to the selector solenoid valve and the proportional solenoidvalve.

- The selector solenoid valve opens a passage between the outer end of the left brakepressure 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 theparking 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.


ParkingBrakeValve

TestSwitch

SelectorSolenoid


Screen

Orifice

LeftDrive Axle

RightDrive Axle

TRACTION CONTROL SYSTEM (TCS)ENGINE RUNNING/LEFT BRAKE ENGAGED

Ball Check

OutputSignals

InputSignals

TransmissionSpeed Sensor


Tcs EngagedLamp

When the signals from the sensors indicate that the left wheel is no longer spinning, thefollowing sequence occurs:

- The Brake ECM stops sending signals to the selector solenoid and the proportionalsolenoid.

- The selector solenoid valve and proportional solenoid valve block the passage to drain andallow the control circuit pressure to increase.

- The left brake reducing valve spool shifts to the center position and blocks the passage todrain.

- 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 fullcontrol of air movement through the radiator with an automatically controlled, variable pitchfan. The fan is designed to help control cooling requirements in specific applications such ascold weather and high altitude. The thermostatic controller automatically adjusts the blade pitchto maintain an optimum engine coolant temperature.

With zero-pitch start-up, the air dam effect prevents air flow through the radiator and the enginereaches the recommended operating temperature more quickly. The pitch will vary throughoutthe day based on the engine cooling temperature and air conditioning requirements. Theautomatic 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 airconditioning pressure sensor (see Visual No. 62) provide input signals to an electronic controlbox located behind the cab (see next page). The electronic control analyzes the input signals andsends an electrical signal to the actuator (3). The actuator rotates and changes the fan pitch asneeded 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 thecompartment behind the operator's station. The control box is used to set up and calibrate theFlexxaire™ fan. Remove the cover from the control box and follow the instructions on the labelinside the cover.

The FlexxaireTM control box provides many features. The customer must decide whichfeatures 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, thefan blades rotate and PUSH air through the radiator. Changing air flow direction canhelp clear debris from the radiator.

Actuator Stall Detection: If the fan pitch actuator encounters excessive resistance (boltfalls into the linkage), the control will sense the increased current and attempt anautomatic calibration. If the obstruction continues, as a safety measure, the control willrotate the fan blades to full pitch.

Second Fluid Temperature Control: A second temperature sensor can be installed tocontrol the fan pitch in addition to the engine coolant temperature sensor (brake oiltemperature).

215


1

2

3 4

Blaze Blocker: A fire suppression system can provide an input signal to the control thatwill rotate the fan blades to the NEUTRAL position. In the NEUTRAL position, the fanprovides no air flow. Limiting the air flow reduces the amount of oxygen to the fire, andthe 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 ofthe actuator.

Temperature Set Point Calibration: This procedure sets the temperature range that thecontroller 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 depressingthe air flow button (3). The nine LED bar display to the right of the air flow button indicates theposition of the fan. The bottom four LED's indicate the PULL direction. The center LEDindicates 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 canbe found in the Service Manual module "FlexxaireTM Fan Installation And MaintenanceManual" (Form SEBC1152).


CONCLUSION

This presentation has provided a basic introduction to the Caterpillar 785C and 789C Off-highway Trucks. All the major component locations were identified and the major systems werediscussed. When used in conjunction with the service manual, the information in this packageshould permit the serviceman to analyze problems in any of the major systems on these trucks.

216


1. 789C model view2. Right side 789C truck3. Front of 789C truck4. Truck body options5. Walk around inspection6. Maintenance checks7. Front wheel bearing8. Front suspension cylinder9. Air filter housing

10. Right side engine11. Transmission charging filter12. Transmission hydraulic tank13. Final drive14. Differential oil level15. Safety cable16. Fuel tank17. Primary fuel filter18. Parking brake and torque converter19. Brake cylinder breathers20. Front air dryer21. 789C engine oil filters22. 785C engine oil filters23. Oil change connector24. Secondary fuel filters25. Engine shutdown switch26. Air filter restriction indicators27. 789C cooling system28. Air cleaner indicators29. Ether cylinders30. Batteries31. Lubrication tank32. Steering system tank33. Air tank drain valve34. Windshield washer reservoir35. Daily checks36. Operator's station37. Operator and trainer seats38. Hoist control lever39. Dash (left side)40. Operator controls41. Switches and signals42. Manual retarder lever

43. Brake and throttle pedals44. Shift console45. Overhead switches46. Circuit breaker panel47. Center dash panel48. Rocker switches49. VIMS message center module50. VIMS interface modules51. VIMS main module52. VIMS diagnostic connector53. Electronic Technician (ET)54. 3516B engine model view55. Electronic control system component

diagram56 Engine ECM57. Atmospheric pressure sensor58. Engine speed/timing sensor59. Throttle position sensor60. EUI fuel injector solenoid61. Input switches and sensors62. Air conditioner compressor switch63. Crankcase pressure sensor64. ECM logged events65. Additional ECM logged events66. Systems controlled by ECM67. Engine oil pre-lubrication68. Speed fan control69. Oil renewal system components70. Oil level switches71. Cooling system72. Radiator73. Water pump74. Coolant 75. Engine (right side)76. Jacket water coolant flow77. Auxiliary (aftercooler) water pump78 Rear aftercooler temperature sensor79. 789C air charging system80. Lubrication system81. Oil filters82. 785C engine oil filters83. Engine oil system

VISUAL LIST


84. Primary fuel filter85. Fuel transfer pump86. Secondary fuel filters87. Fuel injectors88. Fuel system circuit89. Air induction and exhaust system90. Turbocharger inlet pressure sensor91. 351B turbochargers92. Exhaust temperature sensor93. 3512B air induction and exhaust system94. Power train components95. Torque converter96. Torque converter (converter drive)97. Torque converter drive (direct drive)98. Torque converter pump (four sections)99. Torque converter charging filter100. Torque converter inlet relief valve101. Torque converter outlet screen102. Brake oil cooler and diverter valve103. Parking brake release valve104. Torque converter lockup clutch valve

(iron)105. Torque converter lockup clutch control

(direct drive)106. Torque converter hydraulic system107. Transfer gears108. Transmission lube supply hose109. Power shift planetary transmission110. Transmission pump111. Transmission scavenge screens112. Transmission charging filter113. Transmission oil cooler bypass valve and

oil cooler114. Transmission charging pump115. Transmission clutch pressures116. ICM transmission controls (sectional

view)117. Transmission hydraulic system118. Rear axle pump119. Pump supply hose120. Oil filter bypass switch

121. Rear axle oil cooling and filter system122. Double reduction planetary gear final

drives123. Transmission/Chassis ECM124. Transmission/Chassis electronic control

system125. Shift lever switch126. Transmission gear switch127. Transmission Output Speed (TOS)

sensor128. Service/retarder brake switch129. Body position sensor130. Steering system131. 789C steering system (no

steer/maximum flow132 785C steering system (hold)133. Steering tank and filter134. 785C steering pump135. 785C steering pump (maximum flow)136. Pump compensator valve137. 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 valve143. Load sensing controller144. 789C solenoid and relief valve manifold145. 785C solenoid and relief valve manifold146. Solenoid and relief valve manifold

(sectional view)147. 789C steering directional valve148. Steering directional valve (no turn)149. Steering directional valve (right turn)150. 785C solenoid and relief valve manifold

and crossover relief valves151. 785C crossover relief system (external

impact)152. 789C Hand Metering Unit (HMU)153. 789C steering accumulators

VISUAL LIST


154. Shutdown control155. Hoist control system156. Hoist lever157. Hoist control position sensor158. Hoist, converter and brake tank159. Hydraulic tanks (rear)160. Two-section hoist pump161. Hoist screens162. Pump supply ports163. Counterbalance valve164. 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 cylinders170. Hoist system (hold)171. Air and brake systems172. Oil cooled brake assembly (cutaway)173. Air charging system174. 789C air dryers175. Service/retarder brake tank176. Pressure protection valve177. Automatic lubrication solenoid air valve178. Parking/secondary brake tank179. 789C air charging system180. Manual retarder valve181. Service brake valve182. Inverter valve signal port183. Brake release valve184. Normal parking and secondary brake

operation185. Parking/secondary brakes released and

parking brakes engaged186. Service brake and manual retarder relay

valve187. Brake oil makeup tank188. 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 schematic193. Brake cooling oil pressure tap194. Brake electronic control system195. Brake ECM (iron)196. Automatic Retarder Control (ARC)

schematic197. Engine Output Speed (EOS) sensor198. Retarder pressure switch199. Service/retarder brake air system200. Hydraulic ARC System201. Hydraulic ARC Valve202. Engine On/ARC Off203. Engine On/ARC On204. Engine Off/ARC Off205. Automatic retarder control schematic

(engaged)206. Steering bleed down control207. Brake cooling diverter solenoid208. Engine Output Speed (EOS) sensor209. Traction Control System (TCS)

schematic210. Wheel speed sensor211. Traction Control System (TCS) valve212. Traction Control System (TCS)

operation (brakes released)213. Traction Control System (TCS)

operation (left brake engaged)214. Flexxaire™ fan215. Flexxaire™ fan electronic control box216. Model rear view

VISUAL LIST


SERV1706-01 - 270 - Handout No. 17/05

VIMS KEYPAD OPERATIONS

The keypad allows the operator or a service technician to interact with the VIMS. Some of thefunctions 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 anevent will remove the event from the display temporarily. Severe events cannot beacknowledged.

GAUGE Key: Displays parameters monitored by the VIMS. Depressing the arrow keys willscroll through the parameters. Entering the parameter number and the GAUGE key selects thatparameter.

F1 Key: Provides additional information on the current event being displayed. ForMAINTENANCE events, the MID, CID, and FMI are displayed. For DATA events, the currentparameter value is displayed (temperature, pressure, rpm).

oht - 785c and 789c - serv1706 - student handout - oct 05

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