systems operation testing and adjusting cat 740 articulated

RENR5134-01July 2001

Systems OperationTesting and Adjusting740 Articulated Truck Power TrainAXM1-Up (Machine)

i01097883

Important Safety InformationMost accidents that involve product operation, maintenance and repair are caused by failure toobserve basic safety rules or precautions. An accident can often be avoided by recognizing potentiallyhazardous situations before an accident occurs. A person must be alert to potential hazards. Thisperson should also have the necessary training, skills and tools to perform these functions properly.

Improper operation, lubrication, maintenance or repair of this product can be dangerous andcould result in injury or death.Do not operate or perform any lubrication, maintenance or repair on this product, until you haveread and understood the operation, lubrication, maintenance and repair information.Safety precautions and warnings are provided in this manual and on the product. If these hazardwarnings are not heeded, bodily injury or death could occur to you or to other persons.

The hazards are identified by the Safety Alert Symbol and followed by a Signal Word such asDANGER, WARNING or CAUTION. The Safety Alert WARNING label is shown below.

The meaning of this safety alert symbol is as follows:

Attention! Become Alert! Your Safety is Involved.The message that appears under the warning explains the hazard and can be either written orpictorially presented.

Operations that may cause product damage are identified by NOTICE labels on the product and inthis publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. Thewarnings in this publication and on the product are, therefore, not all inclusive. If a tool, procedure,work method or operating technique that is not specifically recommended by Caterpillar is used,you must satisfy yourself that it is safe for you and for others. You should also ensure that theproduct will not be damaged or be made unsafe by the operation, lubrication, maintenance orrepair procedures that you choose.The information, specifications, and illustrations in this publication are on the basis of information thatwas available at the time that the publication was written. The specifications, torques, pressures,measurements, adjustments, illustrations, and other items can change at any time. These changes canaffect the service that is given to the product. Obtain the complete and most current information beforeyou start any job. Caterpillar dealers have the most current information available. For a list of the mostcurrent publication form numbers available, see the Service Manual Contents Microfiche, REG1139F.

When replacement parts are required for thisproduct Caterpillar recommends using Caterpil-lar replacement parts or parts with equivalentspecifications including, but not limited to, phys-ical dimensions, type, strength and material.

Failure to heed this warning can lead to prema-ture failures, product damage, personal injury ordeath.

3Power Train

Table of Contents

Table of Contents

Systems Operation SectionGraphic Color Codes ............................................ 4General Information .............................................. 5Torque Converter ................................................. 6Transmission Planetary ......................................... 8Output Transfer Gears ......................................... 9Interaxle Differential .............................................. 11Differential (Front and Rear Axle) ......................... 13Differential (Center Axle) ....................................... 15Final Drive ............................................................ 18Power Train Hydraulic System ............................. 19Transmission Hydraulic Control ........................... 23Power Train Electronic Control System ................. 24Output Transfer Gears Lubrication System ........... 28Pressure Control Valve (Transmission) ................. 30Selector and Pressure Control Valve(Transmission) ..................................................... 37

Rotary Actuator (Transmission) ............................ 40

Testing and Adjusting SectionTroubleshootingMachine Preparation for Troubleshooting ............. 42General Troubleshooting Information .................... 42Visual Inspection ................................................... 43Operational Checks .............................................. 44Torque Converter Troubleshooting ........................ 45Transmission Planetary Troubleshooting .............. 47Interaxle Differential Troubleshooting .................... 52Differential Troubleshooting .................................. 53

Testing and AdjustingPower Train Pressures .......................................... 55Transmission Hydraulic Control - Test and Adjust .. 73Transmission Shift Points - Test ............................ 82Interaxle Differential - Test .................................... 84Differential - Test ................................................... 85

Index SectionIndex ..................................................................... 88

4Power TrainSystems Operation Section

Systems Operation Sectioni01481554

Graphic Color CodesSMCS Code: 4000

g00771291Illustration 1

(A) Red ........................... Pump discharge pressure

(B) Red Stripes and WhiteStripes .......................... First pressure reduction

(C) Red Dots ................ Second pressure reduction

(D) Orange ............................. Pilot system pressure

(E) Orange Stripes and WhiteStripes .............. Reduced pilot system pressure

(F) Blue .................................................. Blocked oil

(G) Green .. Suction oil, return oil, and case drain oil

(H) Yellow ..................................... Moving parts andactivated valve sections

(I) Purple ........................................ Pressurized gas

(J) Gray ............................... Cutaway sections, andnon-activated valve sections

5Power Train

Systems Operation Section

i01563882

General InformationSMCS Code: 3030

g00791946Illustration 2(1) Engine(2) Torque converter(3) Transmission planetary(4) Wheel and final drive(5) Differential and bevel gear(6) Output transfer gears and case

(7) Drive shaft(8) Through hitch drive shaft(9) Drive shaft(10) Differential and bevel gear(11) Drive shaft(12) Differential and bevel gear

(13) Wheel and final drive(14) Wheel and final drive(15) Differential(16) Front drive shaft(17) Main drive shaft

Tractor ArrangementThe engine flywheel drives torque converter (2).The torque converter has an integral lockup clutch.The lockup clutch for the torque converter allowsthe machine to operate in torque converter drive orin direct drive.

Torque converter (2) is located within the housingfor the transmission planetary which is bolteddirectly to the engine. Transmission planetary (3)contains seven hydraulically actuated clutches. Theseven hydraulically actuated clutches give sevenforward speeds and one reverse speed.

Main drive shaft (17) transmits torque to outputtransfer gears and case (6). Differential (15) islocated in output transfer gears and case (6), whichis connected to front drive shaft (16) and drive shaft(7). Front drive shaft (16) is connected to differentialand bevel gear (5). Drive shaft (7) is connectedhitch drive shaft (8).

Differential and bevel gear (5) transfers drive towheel and final drives (4) for the front axle.

Trailer ArrangementThrough hitch drive shaft (8) transmits torque todrive shaft (9). The drive shaft transfers drive todifferential and bevel gear (10).

Differential and bevel gear (10) transfers drive towheel and final drives (14) for the center axle anddrive shaft (11).

Drive shaft (11) transmits torque to differential andbevel gear (12).

Differential and bevel gear (12) transfers drive towheel and final drives (13) for the rear axle.


i01523695

Torque ConverterSMCS Code: 3101

g00791571Illustration 3(1) Housing(2) Turbine(3) Stator(4) Shaft

(5) One-way clutch(6) Impeller(7) Lockup Clutch(8) Hub

The torque converter is driven by the engineflywheel. The torque converter consists of impeller(6), turbine (2), lockup clutch (7), and stator (3)which incorporates one-way clutch (5). The lockupclutch permits the machine to operate in directdrive in order to keep the power loss at a minimum.The one-way clutch holds the stator when torqueconverter drive is used. The one-way clutch allowsthe stator to turn freely when direct drive is used.

The torque converter housing is fastened to theflywheel housing for the engine. Shaft (4) connectsthe torque converter to the transmission planetarygroup.

The engine flywheel turns rotating housing (1) andimpeller (6). The impeller directs oil onto the bladesof turbine (2). This causes the turbine to turn. Theturbine directs the oil onto stator (3). This causesthe stator to try to turn in the opposite directionof the turbine. The movement of the stator causesthe rollers of one-way clutch (5) to move betweenstator (3) and the carrier for the stator. The actionof the one-way clutch keeps the stator from rotatingin the opposite direction to the turbine. The statornow directs most of the oil back to the impeller.The remainder of the oil goes out of the torqueconverter. The oil, that goes back to the impellerfrom the stator, moves in the same direction as therotation of the impeller. Since this oil is moving inthe same direction as the impeller, the torque outputfrom the torque converter is multiplied.

Turbine (2) turns hub (8). The hub turns shaft (4).Power is sent through the shaft to the transmissionplanetary group.

7Power Train


Lockup clutch (7) is part of the torque converter.The lockup clutch is located between the engineflywheel and the turbine. The lockup clutch isengaged under the following conditions: sufficientinput speed to the transmission planetary group,sufficient oil pressure in the transmission planetarygroup, and sufficient engine rpm. When thelockup clutch is engaged, the impeller and theturbine turn at the same speed as the engine andthere is no loss of power in the torque converter.The connection between the engine and thetransmission planetary group is now direct.

Torque converter drive is available in the first gearand reverse gear. The lockup clutch provides directdrive once the transmission speed and the enginespeed are matched.

Direct drive is provided in all the higher gears. Thelockup clutch is disengaged during transmissionshifts in order to allow a smooth transition betweengears.

The input speed of the torque converter is measuredat the engine flywheel. This speed is the samespeed as the engine output speed. The outputspeed of the torque converter is measured at theplanetary transmission. This speed is the samespeed as the transmission input speed.


i01523914

Transmission PlanetarySMCS Code: 3160

g00791642Illustration 4(1) Clutch 1(2) Clutch 2(3) Clutch 3(4) Clutch 4(5) Clutch 5

(6) Clutch 6(7) Clutch 7(8) Sensor (output speed)(9) Output yoke(10) Shaft (input from torque converter)

The planetary transmission has seven forwardspeeds and one reverse speed. At lower groundspeeds, FIRST speed uses torque converter drive.At higher ground speeds, FIRST speed uses directdrive. As the ground speed increases in FIRSTspeed the lockup clutch of the torque converterengages. This provides FIRST speed with directdrive. The torque converter is always in direct drivefor speeds SECOND through SEVENTH, but thereis a short period of torque converter drive whenthe clutches engage in the planetary transmission.Only torque converter drive is used when REVERSEspeed is selected. The torque converter lockupclutch is disengaged during transmission shifts inorder to provide smooth shifts. Table 1 shows theclutches that are engaged for each speed.

Table 1

SPEED SELECTIONSPEED ENGAGED CLUTCHES

NEUTRAL 1

REVERSE speed 3 & 7FIRST speed 2 & 6

SECOND speed 1 & 6THIRD speed 3 & 6

FOURTH speed 1 & 5FIFTH speed 3 & 5

SIXTH speed 1 & 4SEVENTH speed 3 & 4

9Power Train


The planetary transmission consists of two rotatingclutches, five stationary clutches, and five planetaryunits. This provides seven forward speeds and onereverse speed. No. 3 clutch (3) and No. 4 clutch (4)are the rotating clutches.

The planetary transmission is bolted to the torqueconverter housing. Shaft (10) is part of the torqueconverter, and the shaft transmits the torque to theplanetary transmission. Output yoke (9) from theplanetary transmission is bolted to the main driveshaft. The main drive shaft connects the planetarytransmission with the output transfer gear.

Sensor (8) measures the output speed of theplanetary transmission. There are two sensorsin order to provide a backup in the event of afailure. The sensors send information about thetransmission output speed to the ECM (ElectronicControl Module).

i01575760

Output Transfer GearsSMCS Code: 3159

g00819173Illustration 5(1) Input Shaft(2) Differential(3) Shaft(4) Gear

(5) Idler Gear(6) Gear(7) Output Yoke(8) Shaft

(9) Gear(10) Gear(11) Output Yoke(12) Solenoid and Relief Valve


Power is transmitted to the output transfer gearsfrom the transmission planetary group via a driveshaft to input shaft (1). The input shaft is splinedto interaxle differential (2) that splits the torquebetween the front and the rear axles. Torque for thefront axle is transmitted from the differential alongshaft (3) to gear (4). An idler gear (5) transfersthis torque to gear (6) in the bottom of the outputtransfer gear case. Gear (6) is splined to the outputyoke (7).

Torque for the rear axles is transmitted from thedifferential along shaft (8) to gear (9). Gear (9) ismeshed with gear (10) which is splined to outputyoke (11).

g00791610Illustration 6This is a view of the solenoid and relief valve from below themachine.

Solenoid and relief valve (12) controls the lubricationoil for the output transfer gears. The solenoid andrelief valve also controls the interaxle differentialand the axle differentials.

11Power Train


i01524199

Interaxle DifferentialSMCS Code: 3287

g00791767Illustration 7(1) Input shaft(2) Shaft(3) Planetary gear(4) Differential housing(5) Clutch pack

(6) Piston(7) Rotating housing(8) Output shaft(9) Output shaft(10) Gear

(11) Gear(12) Sun gear(13) Planetary gear(14) Sun gear(15) Hub

Torque from the transmission planetary entersthe output transfer gears, and flows directly todifferential housing (4). The torque is transmittedthrough the interaxle differential to output shaft (8)and output shaft (9).

The interaxle differential allows the torque from thetransmission planetary to be divided between thefront axle and the two rear axles.

The front axle receives a smaller proportion of thetorque than the center and rear axles. This preventsexcess torque from being transmitted to the frontaxle.

The distance from the axis of rotation of differentialhousing (4) to the axis of planetary gears (3) isgreater than the distance to the axis of planetarygears (13).

Planetary gears (3) transfer the torque fromdifferential housing (4) to output shaft (9) andplanetary gears (13) transfer the torque fromdifferential housing (4) to output shaft (8).

The torque that is transmitted to output shaft (9) isgreater than the torque that is transmitted to outputshaft (8).

Output shaft (9) transmits the torque to the two rearaxles and output shaft (8) transmits the torque tothe front axle.

The torque that is transmitted to the two rear axlesis greater than the torque that is transmitted to thefront axle. 40% of the torque is transmitted to thefront axle and 60% of the torque is transmitted tothe center and the rear axle.


If the machine was operated on a hard surface withequal traction at each wheel, turning the machinewould cause torsional stresses in the power train.This could reduce the service life of componentsin the power train.

The interaxle differential transmits drive to the frontand rear axles at equal speeds when the machineis travelling straight. The interaxle differential alsotransmits drive to the front and rear axles at differentspeeds when the machine is turning. Torque input ismaintained at each axle throughout each operation.

The interaxle differential responds to the differencein resistance between the front wheels and thecenter and rear wheels. This is carried out ina similar manner to the response of the axledifferentials to the speed difference between theinner wheels and the outer wheels.

The interaxle differential is equipped with a lockupclutch. The lockup clutch is activated by a floormounted switch. The lockup clutch will neutralizenormal interaxle differential operation and transferdrive to all three axles regardless of the groundconditions or the rolling resistance at each wheel.

The interaxle differential consists of an input shaft(1) which is connected to differential housing (4).Differential housing (4) contains two pairs of threeevenly spaced shafts (2). The shafts are used tosupport two planetary gear sets (3) and (13). Bothplanetary gear sets are in constant mesh with eachother and each of the gears is free to rotate aroundshafts (2).

Planetary gear set (3) is in constant mesh with sungear (14) which is installed onto output shaft (9)for the output drive to the trailer. Planetary gear set(13) is in constant mesh with sun gear (12) whichis installed onto output shaft (8) for the output driveto the tractor.

When the machine is moving in a straight directionwith equal ground resistance at each wheel thedifferential housing (4), planetary gears (3) andplanetary gears (13) rotate as a unit.

When the machine is turning, the turning radiuschanges at the front wheels and at the rear wheels.Planetary gears (3) and (13) rotate around shafts(2) as sun gear (14) for the drive to the trailer slowsdown.

If wheel spin occurs at the front of the machine,drive to the center axle and drive to the rear axlewould be reduced to a degree that would stopthe machine. In this event, engaging the interaxledifferential lock would restore drive to all axles.The differential effect is cancelled by locking thedifferential housing to the output shafts.

When the operator engages the differential lock, oilpressure is transmitted by the solenoid and reliefvalve to rotating housing (7). The oil pressure insiderotating housing (7) acts on piston (6) which forcesthe piston against clutch pack (5). Hub (15) anddifferential housing (4) are then connected. Bothplanetary gear sets and both sun gears are lockedin position. The differential effect is cancelled. Shaft(8) and shaft (9) will rotate at the same speed.

When the operator disengages the differential lock,oil pressure is relieved at piston (6). This allowsclutch pack (5) to disengage. Differential housing(4) and hub (15) are disconnected and the interaxledifferential effect is restored.

13Power Train


i01551675

Differential (Front and RearAxle)SMCS Code: 3258-RE; 3258-FR

g00766546Illustration 8Differential(1) Bevel pinion shaft(2) Oil supply tube(3) Chamber(4) Piston(5) Pressure plate(6) Rotating plate

(7) Friction disc(8) Hub assembly(9) Axle shaft(10) Side gear(11) Differential case(12) Spider

(13) Pinion gear(14) Axle shaft(15) Side gear(16) Bevel gear

A differential is an arrangement of gears whichenables one shaft to drive two shafts with equaltorque. The differential also allows the two shafts torotate at different speeds.

The differential in an axle enables drive to bemaintained to both wheels through separate axleshafts when the machine is turning. The wheel onthe inside of the turn will travel a shorter distancethan the wheel on the outside of the turn. Thiscauses the wheel on the inside of the turn to slowdown while the wheel on the outside of the turnspeeds up.

In adverse ground conditions, one or more ofthe wheels may lose traction. The action of thedifferential will result in a loss of drive as thedifferential allows the torque to be transmitted alongthe path of least resistance, which will be the wheelthat is slipping.

The differential in each axle can be locked inadverse conditions. Locking the differential providesdirect drive to all the wheels at the same speedregardless of the resistance due to traction.


A differential divides the power that is sent to themachine wheels. During a turn, the inside wheelturns at a slower rate than the outside wheel. Thedifferential still sends the same amount of torqueto each wheel. Each differential has a differentiallock. The main component of the differential lock isthe clutch pack. When the differential lock switchesare engaged, the clutch pack connects one axleshaft to the differential case. Both axle shafts areconnected in order to form a solid axle with nodifferential effect.

The inside components of the differential receivelubrication from the oil that is inside the axlehousing.

Bevel pinion shaft (1) is in constant mesh with bevelgear (16). The bevel pinion shaft and the bevelgear provide a gear reduction and a change in thedirection of drive by 90.

Differential case (11) is attached to bevel gear(16). The differential case holds spiders (12). Fourpinion gears (13) are free to rotate around thespiders. Side gears (10) and (15) are mounted inthe differential case. The side gears are meshedwith the pinion gears. Axle shafts (9) and (14) aresplined into the side gears.

When the bevel gear (16) is turned by bevel pinionshaft (1), differential case (11) is also turned. Ifthe resistance between each of the road wheelsis equal, pinion gears (13) will not rotate aroundspiders (12). The pinion gears will turn with thespiders. The pinion gears will turn the side gearswith equal speed and equal torque.

When the machine is turning, the wheel that is onthe inside of the turn will travel a shorter distancethan the wheel on the outside of the turn. Thiscauses the wheel on the inside of the turn to slowdown while the wheel on the outside of the turnspeeds up.

The axle shaft on the inside of the turn and the sidegears on the inside of the turn slow down. Thiscauses the pinion gears to rotate on the spiders.

The wheel, the axle shaft and the side gear onthe inside will slow down as the machine turns.The wheel, the axle shaft and the side gear on theoutside will speed up in proportion to the insidewheel. The differential between the speed of thetwo wheels is taken up by the rotation of the bevelgears around the spiders. Both wheels are drivenwith equal force, but at different speeds.

When one wheel has more traction than the otherwheel, the torque travels by the path of leastresistance to the wheel that has less traction. Thewheel with less traction will spin and the wheelthat has traction will be stationary. In this condition,the machine will lose drive. A differential lock isprovided in order to prevent loss of drive in adverseconditions.

Differential Lock Operation

The axle differential lock should be engaged whenthe machine is being operated on a loose surfaceor a soft surface. The axle differential lock shouldalso be engaged if wheel spin is experienced andadditional traction is required. Damage can occur todrive line components through a buildup of torsionalstress, if operating the machine on a hard surfacewith the axle differential lock engaged. The machineshould only be driven in a straight line when theaxle differential lock is engaged.

When the differential lock switches are operated,oil pressure is transmitted through oil supply tube(2) into chamber (3). Piston (4) is offset againstpressure plate (5) which forces rotating plates (6)and friction discs (7) together, locking axle shaft (9)to hub assembly (8). This prevents side gear (10)from rotating inside differential case (11). Piniongears (13) stop revolving and this causes side gear(15) and axle shaft (14) to lock. Both axle shaftsnow rotate at the same speed as the bevel gearand differential case.

15Power Train


i01515596

Differential (Center Axle)SMCS Code: 3258-CE

g00786475Illustration 9Differential(1) Bevel pinion shaft(2) Gear(3) Oil supply tube(4) Chamber(5) Piston(6) Pressure plate

(7) Rotating plate(8) Friction disc(9) Hub assembly(10) Axle shaft(11) Side gear(12) Differential case

(13) Spider(14) Pinion gear(15) Axle shaft(16) Side gear(17) Bevel gear(18) Differential carrier

A differential is an arrangement of gears whichenables one shaft to drive two shafts with equaltorque. The differential also allows the two shafts torotate at different speeds.

The differential in an axle enables drive to bemaintained to both wheels through separate axleshafts when the machine is turning. The wheel onthe inside of the turn will travel a shorter distancethan the wheel on the outside of the turn. Thiscauses the wheel on the inside of the turn to slowdown while the wheel on the outside of the turnspeeds up.

In adverse ground conditions, one or more ofthe wheels may lose traction. The action of thedifferential will result in a loss of drive as thedifferential allows the torque to be transmitted alongthe path of least resistance, which will be the wheelthat is slipping.

The differential in each axle can be locked inadverse conditions. Locking the differential providesdirect drive to all the wheels at the same speedregardless of the resistance due to traction.


A differential divides the power that is sent to themachine wheels. During a turn, the inside wheelturns at a slower rate than the outside wheel. Thedifferential still sends the same amount of torqueto each wheel. Each differential has a differentiallock. The main component of the differential lock isthe clutch pack. When the differential lock switchesare engaged, the clutch pack connects one axleshaft to the differential case. Both axle shafts areconnected in order to form a solid axle with nodifferential effect.

The inside components of the differential receivelubrication from the oil that is inside the axlehousing.

Bevel pinion shaft (1) is in constant mesh with bevelgear (17). The bevel pinion shaft and the bevelgear provide a gear reduction and a change in thedirection of drive by 90.

Differential case (12) is attached to bevel gear(17). The differential case holds spiders (13). Fourpinion gears (14) are free to rotate around thespiders. Side gears (11) and (16) are mounted inthe differential case. The side gears are meshedwith the pinion gears. Axle shafts (10) and (15) aresplined into the side gears.

When the bevel gear (17) is turned by bevel pinionshaft (1), differential case (12) is also turned. Ifthe resistance between each of the road wheelsis equal, pinion gears (14) will not rotate aroundspiders (13). The pinion gears will turn with thespiders. The pinion gears will turn the side gearswith equal speed and equal torque.

When the machine is turning, the wheel that is onthe inside of the turn will travel a shorter distancethan the wheel on the outside of the turn. Thiscauses the wheel on the inside of the turn to slowdown while the wheel on the outside of the turnspeeds up.

The axle shaft on the inside of the turn and the sidegears on the inside of the turn slow down. Thiscauses the pinion gears to rotate on the spiders.

The wheel, the axle shaft and the side gear onthe inside will slow down as the machine turns.The wheel, the axle shaft and the side gear on theoutside will speed up in proportion to the insidewheel. The differential between the speed of thetwo wheels is taken up by the rotation of the bevelgears around the spiders. Both wheels are drivenwith equal force, but at different speeds.

When one wheel has more traction than the otherwheel, the torque travels by the path of leastresistance to the wheel that has less traction. Thewheel with less traction will spin and the wheelthat has traction will be stationary. In this condition,the machine will lose drive. A differential lock isprovided in order to prevent loss of drive in adverseconditions.

Differential Lock Operation

The axle differential lock should be engaged whenthe machine is being operated on a loose surfaceor a soft surface. The axle differential lock shouldalso be engaged if wheel spin is experienced andadditional traction is required. Damage can occur todrive line components through a buildup of torsionalstress, if operating the machine on a hard surfacewith the axle differential lock engaged. The machineshould only be driven in a straight line when theaxle differential lock is engaged.

When the differential lock switches are operated,oil pressure is transmitted through oil supply tube(3) into chamber (4). Piston (5) is offset againstpressure plate (6) which forces rotating plates (7)and friction discs (8) together, locking axle shaft(10) to hub assembly (9). This prevents side gear(11) from rotating inside differential case (12). Piniongears (14) stop revolving and this causes side gear(16) and axle shaft (15) to lock. Both axle shaftsnow rotate at the same speed as the bevel gearand differential case.

Center Axle Through Drive


The center axle on the 740 features a through drivein order to transmit drive to the rear axle.

17Power Train


g00807440Illustration 11(1) Bevel pinion shaft(2) Gear

(17) Bevel gear(19) Gear assembly

Drive is input to the axle from the drive shaft to gearassembly (19). Gear assembly (19) is meshed withgear (2) on bevel pinion shaft (1). This provides thedrive to bevel gear (17).

Drive to the rear axle is carried by gear assembly(19) to an output shaft that connects to the driveshaft to the rear axle via a universal joint.


i01515331

Final DriveSMCS Code: 4050

g00786313Illustration 12Final Drive (Front and Center Axle)(1) Wheel(2) Ring gear(3) Planetary carrier(4) Spindle(5) Axle shaft(6) Sun gear(7) Hub(8) Gear(9) Wheel bearings(10) Seals(11) Brake (Front axle and center axle)

g00807179Illustration 13Final Drive (Rear Axle)(1) Wheel(2) Ring gear(3) Planetary carrier(4) Spindle(5) Axle shaft(6) Sun gear(7) Hub(8) Gear(9) Wheel bearings(10) Seals

Planetary final drives are used on all axles.

Ring gear (2) is mounted on hub (7). The hub issplined onto spindle (4). Spindle (4) is bolted to theaxle housing. Ring gear (2) is held stationary.

Gears (8) are mounted upon planetary carrier (3)which is bolted to wheel (1). Sun gear (6) is splinedto axle shaft (5).

Drive comes to sun gear (6) through axle shaft (5).Ring gear (2) is held stationary, so the planetarycarrier is driven in the same direction as the sungear at a reduced speed. The carrier is bolted tothe wheel and the wheel rotates on bearings (9).

The final drive is lubricated by oil from the axle.Seals (10) allow the oil to be sealed in the finaldrive and the axle.

19Power Train


i01528758

Power Train Hydraulic SystemSMCS Code: 3000; 3100; 4000

The hydraulic system for the power train consists oftwo separate subsystems.

The first system supplies oil to the torque converterand the planetary transmission.

The second system supplies oil to the outputtransfer gear, the interaxle differential lock and thethree axle differential locks.

Torque Converter and Transmission


The transmission hydraulic control system providespressurized oil to the clutches of the transmissionplanetary. , Pressurized oil is also supplied to thetorque converter and to the torque converter lockupclutch.

Oil from the sump (1) of the torque converter isdrawn through suction screen (2) by oil pump (3).

Oil from the pump is supplied through oil filter (4)to downshift solenoid (5) and upshift solenoid (6).Oil is also supplied to selector and pressure controlvalve (13). Downshift solenoid (5) and upshiftsolenoid (6) control the flow of pressurized oil torotary actuator (7). Rotary actuator (7) determinesthe position of selector spool (12) in selector andpressure control valve (13).


Selector spool (12) in selector and pressure controlvalve (13) allows pilot oil to flow to individual valves(8) on pressure control valve (9). The position of theselector spool determines the path of the pilot oilto the individual valves.

Each individual valve is a modulating valve whichcontrols the pressure of the oil that is supplied tothe clutches in the transmission planetary.

Oil from the selector and pressure control valve alsosupplies the torque converter. The oil that is usedby the torque converter is then sent through thetransmission oil cooler and back to the transmissionas lubricant.

Transmission Oil Pump and SuctionScreen

g00792128Illustration 15(3) Oil pump (transmission)(14) Port (inlet)(15) Idler gear(2) Suction screen(16) Torque converter housing(17) Gear

g00792091Illustration 16(3) Oil pump (transmission)(14) Port (inlet)(18) Hose (pump drive group lubrication)(19) Port (outlet)

Oil pump (15) for the transmission oil is located inthe top of torque converter housing (16).

The oil pump is splined to gear (17) which is drivenby the input to the torque converter via idler gear(15).

The oil is drawn by the oil pump from the sump inthe torque converter housing. The oil then passesthrough suction screen (2) to port (14) in the oilpump. The oil is then pumped from port (19) to thesystem. Hose (18) receives oil from the system inorder to lubricate the pump drive group.

21Power Train


Transmission Oil Filter

g00792383Illustration 17(20) Transmission oil filter base(21) Filter element(22) Cavity (oil inlet)(23) Spool (bypass valve)(24) Cavity (oil outlet)(25) Spring (bypass valve)

g00792384Illustration 18Location of transmission oil filter

The transmission oil filter is located on the right sideof the engine.

The oil enters oil filter base (20) through cavity (22).The oil flows from cavity (22) through filter element(21) into cavity (24) and out of the filter base.

If there is a restriction in the filter element the oilpressure in the filter increases. The increased oilpressure shifts spool (23) to the right against spring(25). When the spool is moved to the right, oil flowsdirectly from cavity (22) to cavity (24). The oil filterelement is now bypassed.

Transmission Oil Cooler

g00792759Illustration 19This is a view from below the transmission oil cooler.

The oil cooler for the transmission is located on theright side of the engine below the oil cooler for thebrake system.

Oil from the torque converter is sent to the oil coolerand the oil is cooled by engine coolant. Oil from theoil cooler is then used to lubricate the transmission,the pump drive group and the accessory drivegroup.


Output Transfer Gears andDifferentials


A second hydraulic circuit supplies lubrication forthe output transfer gears. The circuit also controlsthe interaxle differential and the axle differentials.

Oil from the sump of the output transfer gears (30)is drawn by charging and scavenging pump (26)through magnetic screen (32) in order to removeany metallic particles that may be present in theoil. The charging and scavenging pump chargesthe output transfer gears and the differential locks.The charging and scavenging pump for the outputtransfer gears and the differential locks is mountedon the top of the flywheel housing to the left of theengine.

The oil from the charging and scavenging pumpis fed via filter (27) to solenoid and relief valve(28) that is mounted on the output transfer gearcase. The solenoid and relief valve controls thelock for interaxle differential (29) and the locks forthe axle differentials. The solenoid and relief valvealso provides lubrication oil for the output transfergear (30).

Operation of the solenoid and relief valve appliesoil pressure to the lockup clutch in the interaxledifferential in order to engage the interaxledifferential lock. Within the solenoid and relief valve,a second solenoid valve controls the axle differentiallocks (31) in the three axles. The circuit allows theaxle differential locks to be engaged only when theinteraxle differential lock is engaged.

23Power Train


Engagement of the axle differential locks is achievedwhen the solenoid valve allows pressurized oil fromthe solenoid and relief valve to fill the clutcheson the differentials in each axle. When the axledifferential lock is unselected, the oil in the clutchesof the axle differentials is able to drain to the topof the output transfer gear case as additionallubrication.

The oil enters the output transfer gear case at thetop. The oil drains down to the sump of the outputtransfer gear case and the oil provides lubricationto the gears and the bearings.

i01536341

Transmission HydraulicControlSMCS Code: 3167



Control of the torque converter and the planetarytransmission is achieved by a selector and pressurecontrol valve that controls the supply of pressurizedoil to the pressure control valve. The pressurecontrol valve contains individual valves that controlthe oil pressure in each clutch and the oil pressurein the torque converter lockup clutch.

Oil is supplied by pump (1) through oil filter (2). Thepressurized oil is available to downshift solenoid(3), upshift solenoid (4) and torque converter lockupclutch solenoid (9). Pressurized oil is also suppliedto selector and pressure control valve (13).

Selector and pressure control valve (13) regulatesthe oil pressure. The selector and pressure controlvalve sends pressurized oil to pressure control valve(7) for clutch actuation. The selector and pressurecontrol valve also provides the pilot signal to theindividual valves (6) in the pressure control valve.

The selector and pressure control valve alsosupplies oil to the torque converter. The maximumpressure of the oil to the torque converter isregulated by relief valve (11) in the selector andpressure control valve.

Rotary actuator (5) is controlled by downshiftsolenoid (3) and upshift solenoid (4). The rotaryactuator turns selector spool (10) in the selectorand pressure control valve. The selector spooldetermines the path of the pilot oil to the individualvalves.

When the machine is in NEUTRAL, the downshiftsolenoid is selected. This ensures that the rotaryactuator holds the selector spool in the correctposition. The selector and pressure control valveincludes a neutralizer valve. Neutralizer valve (12)prevents pressurized oil from being supplied to theselector spool unless the engine is started with thetransmission control in the NEUTRAL position.

When the operator selects drive, the ECM for thepower train closes downshift solenoid (3) and opensupshift solenoid (4). The upshift solenoid suppliespressurized oil to the rotary actuator. This causesthe rotary actuator to rotate. This turns the selectorspool in the selector and pressure control valve.Pilot oil is directed by the selector spool to theindividual valves for clutch 2 and clutch 6.

Solenoid valve (9) for the torque converter lockupclutch is closed. This allows torque converter driveas the machine accelerates. As the machine speedmatches the engine speed, the ECM for the powertrain sends an electrical signal to the solenoid valvefor the torque converter lockup clutch. This allowsa pilot oil supply to the modulating valve (8) forthe torque converter lockup clutch. This causesthe torque converter lockup clutch to engagedirect drive between the engine and the planetarytransmission.

The ECM reads the information from the engineoutput speed sensor and from the transmissionoutput speed sensor. The ECM shifts thetransmission at predetermined speeds.

Table 2

SPEED SELECTIONSPEED ENGAGED CLUTCHES

NEUTRAL 1

REVERSE speed 3 & 7FIRST speed 2 & 6

SECOND speed 1 & 6THIRD speed 3 & 6

FOURTH speed 1 & 5FIFTH speed 3 & 5SIXTH speed 1 & 4

SEVENTH speed 3 & 4

i01545381

Power Train Electronic ControlSystemSMCS Code: 4800

Control of the power train is achieved byelectronically controlled hydraulic actuation. Controlof the power train is maintained by the electroniccontrol module.

The electronic control module is also responsiblefor controlling the other systems that are used onthe machine.

The ECM receives inputs from different sensors andfrom operator requests. The ECM sends electronicsignals in order to control transmission shifts andother power train components.

The ECM receives the following inputs:

Engine output speed

25Power Train


Transmission output speed

Selected gear

Position of the transmission control lever

Position of the selector spool

Position of the hoist lever

Differential lock switch

Position of the engine compression brake control

Transmission hold

Key start switch

High gear limit

Status of the parking brake

Status of the service brakes

System faults

The following functions are carried out by the ECM:

Automatic transmission shifts

Direct drive (torque converter lockup)

Transmission hold

Overspeed control

Directional shift management

Protection against abusive shifts

The ECM also carries out other functions whichinclude control of the secondary steering systemand control of the hoist system.

The ECM will also control default mode operation inthe event of electrical failure.

A service technician can use Caterpillar ET tocommunicate with the ECM. The service techniciancan interrogate the ECM for details of faults and theservice technician can monitor operating conditions.


Power Train Electronic ControlSystem

g00808163Illustration 22Block diagram of the power train electronic control system(1) Service tool connector(2) CAT Data Link(3) Caterpillar Monitoring System(4) Caterpillar Monitoring System service

connector(5) Electronic control module (ECM)

(6) Torque converter lockup clutch solenoid(7) Downshift solenoid(8) Upshift solenoid(9) Transmission gear sensor(10) Transmission control(11) Engine

(12) Engine speed sensor(13) Torque converter(14) Transmission(15) Transmission output speed sensors

(two)

Seven hydraulically activated clutches intransmission (14) provide seven forward speedsand one reverse speed. Speed selections anddirection selections are made manually by usingtransmission control (10).

The power train electronic control systemelectronically controls the shifting of thetransmission. In order for the transmission to beshifted to the desired speed and the desireddirection, the ECM (5) receives the operator inputfrom transmission control (10). The ECM sends asignal to downshift solenoid (7) or upshift solenoid(8). The downshift solenoid and the upshift solenoidturn the rotary actuator which turns the selectorspool in the selector and pressure control valve.The modulating valves in the pressure control valvemodulate the oil pressure of the clutches that areselected.

A modulating valve is also used to control oilpressure to the torque converter lockup clutch. Pilotoil is supplied to the modulating valve for the torqueconverter lockup clutch by torque converter lockupclutch solenoid (6). The torque converter lockupclutch provides direct drive between the engine andthe transmission planetary.

The power train ECM uses input signals fromthe following components to ensure correctengagement of the clutches: engine speed sensor(12) and transmission output speed sensors (15).

The power train ECM also controls the followingfunctions: interaxle differential lock, axle differentiallocks, hoist control, and secondary steering system.

27Power Train


Electronic Control ModuleThe electronic control module (ECM) is located atthe right rear side of the cab. The ECM controlsthe shifting of the transmission. The transmissioncontrol sends the operator input to the ECM. Theoperator input indicates the desired speed forthe transmission and the desired direction for thetransmission. The ECM makes decisions that arebased on the input information and on the memoryinformation. After the ECM receives the inputinformation and the memory information, the ECMsends a corresponding response to the outputs.The inputs and the outputs are connected to themachine harness by two 40-pin connectors.

InputsThe machine has several input devices. Inputdevices inform the ECM of the operating conditionsof the machine. The machine has two types ofinputs, switch inputs and sensor inputs. The switchinputs of the ECM are provided with the followingsignals from the switches: an open, a ground, anda +battery. Sensors provide a constantly changingsignal to the ECM.

OutputsThe ECM responds to decisions by sendingelectrical signals through the outputs. The outputscan create an action or the outputs can provideinformation to the ECM.

Input/OutputThe CAT Data Link is used to communicate with theother electronic control modules on the machine.The CAT Data Link is bidirectional. The CAT DataLink allows the sharing of information with otherelectronic controls.

The ECM receives the harness code input fromthe Caterpillar Monitoring System.

The ECM sends the following information to theCaterpillar Monitoring System: engine speed,machine ground speed, parking brake switchstatus, transmission speed selection, and servicecode of the transmission.

The monitoring system displays this informationfor the operator or for service personnel.

The ECM communicates with the engine ECM inorder to allow controlled throttle shifting.

Sensors In The Power TrainSensors provide information to the power trainelectronic control module (ECM) about changingconditions. The sensor signal changes proportionallyto the changing conditions. The following type ofsensor signals are recognized by the power trainECM.

Frequency signals: The frequency (Hz) of thesensor signal varies as the condition changes.

Transmission Gear Sensor

g00616555Illustration 23Transmission Gear Sensor

The transmission gear sensor is an input to thePower Train ECM. The sensor tells the ECM theposition of the rotary actuator and the selectorspool. The sensor is connected mechanically to therotary actuator of the transmission.


Speed Sensors (Engine Output andTransmission Output)

g00288428Illustration 24Typical Speed Sensor

There are two transmission output speed sensorsand one engine output speed sensor on themachine. The speed sensors are inputs of theECM. These speed sensors are frequency sensors.Frequency sensors produce a signal (Hz) whichvaries as the condition changes. The sensorgenerates a sine wave signal from the gear teethas the gear teeth pass the sensor. The sensorproduces a signal that equals one pulse per geartooth. This signal is sent to the ECM. The ECMmeasures the frequency of the signal in order todetermine the speed of the condition. The ECMreceives signals from the speed sensors. The ECMuses the input from the speed sensors in orderto determine the speed of the system. The ECMuses the input from the speed sensors in order toregulate transmission shifts. Each speed sensor hastwo connections to the ECM (+ and ).

For all of the speed sensors, connector contact2 is the signal line and connector contact 1 isthe return line. Two transmission speed sensorsmeasure transmission output speed in order toprovide protection against failure.

Note: The speed sensors are used to diagnoseeach other during normal operation. The ECMperiodically checks the value from the speedsensor. If an incorrect value is found, the ECM willlog a service code that indicates a fault for a speedsensor circuit.

i01562748

Output Transfer GearsLubrication SystemSMCS Code: 1300; 3159

The lubrication of the output transfer gears isachieved by a separate hydraulic system fromthe hydraulic system that serves the planetarytransmission and the torque converter . Thelubrication system for the output transfer gears alsoprovides oil for the axle differential locks and for theinteraxle differential lock that is located in the casefor the output transfer gears.

Charging and Scavenging Pumpfor the Output Transfer Gears andDifferential Locks

g00797836Illustration 25Charging and scavenging pump for the output transfer gears anddifferential locks

Charging and scavenging pump (1) supplies oilfor the lubrication of the output transfer gears. Thecharging and scavenging pump also supplies oil forthe control of the interaxle differential lock and theaxle differential locks. The charging and scavengingpump is driven from the engine flywheel via an idlergear.

29Power Train


Oil Filter for the Output TransferGears

g00790144Illustration 26Oil filter for the output transfer gears

Oil is supplied to oil filter (2) from the gear pump.The oil filter is located behind the cab on the left ofthe machine. The base of the oil filter contains abypass valve in order to allow the oil to continue tothe output transfer gears in the event of a blockagein the oil filter. A switch notifies the operator in theevent of a blockage in the oil filter.

Solenoid and Relief Valve

g00797846Illustration 27Solenoid and relief valve

Oil from the oil filter is then fed to solenoid and reliefvalve (3) that is mounted on the case of the outputtransfer gears.

The solenoid and relief valve provides oil to theoutput transfer gears and the differential locks.

The solenoid and relief valve incorporates twosolenoid valves, a priority valve and a relief valve.

One solenoid in the solenoid and relief valvecontrols the oil to the interaxle differential lock andthe oil to the solenoid valve for the axle differentiallocks.

A second solenoid controls the oil to the axledifferential locks.

The priority valve gives priority to the oil supplyfor the differential locks over the oil supply to theoutput transfer gears.

The relief valve regulates the maximum pressure inthe output transfer gears and the differential locksystem.

Oil from the solenoid and relief valve enters thecase for the output transfer gears at the top. The oilis gravity fed to the output transfer gears.

Magnetic Screen for the OutputTransfer Gears

g00797837Illustration 28Magnetic screen for the output transfer gears

Oil is scavenged from the case of the output transfergears through magnetic screen (4). The magneticscreen collects any ferrous debris that may bepresent in the oil for the output transfer gears.


i01540730

Pressure Control Valve(Transmission)SMCS Code: 3074

Transmission Pressure ControlValve


31Power Train


Pressure control valve (1) has seven modulationreduction valves (2) for the transmission planetaryand one modulation reduction valve (3) for thetorque converter lockup clutch. There is onemodulation reduction valve for each clutch in thetransmission planetary. Each modulation reductionvalve acts separately. This is known as IndividualClutch Modulation (ICM). The modulation reductionvalves control the amount of pressure that will beused for clutch engagement and for the release ofthe clutch. The modulation reduction valves alsodetermine the duration of clutch engagement.

Each load piston body (4) has an identification letterfor the purposes of disassembly and assembly.Pilot passages (5) are connected to passagesfrom the rotary selector spool of the selector andpressure control valve. Pump oil from the selectorand pressure control valve is in passage (6). Drainpassages (7) are connected to the transmissioncase reservoir.

All of the modulation reduction valves operate in asimilar way, so only the basic operation is provided.

The Beginning of a Shift and the Clutchis Filling



When a shift is started, pilot passage (5) receivespilot oil at the correct sequence from the rotaryselector spool. Selector piston (8) and loadpiston (9) move against the force of springs (10).Modulation reduction valve (11) moves againstthe force of spring (12). Passage (13) is blockedto drain passage (14). Passage (13) is open topassage (6). The pump oil now begins to fill theclutch. The pressure of the oil that is filling the clutchis balanced against the force of springs (10) as thesprings are compressed by the selector piston. Thisis the primary pressure for the clutch. The primarypressure helps to fill the clutch smoothly in order toavoid harsh transmission shifts.

As the oil flows to passage (13), oil is able to flowthrough load piston orifice (15) and passage (16).

Completed Shift with an Engaged Clutch


33Power Train


After the clutch is full of oil, the pressure of thepump oil in the selected clutch increases. Thepressure of the oil that is flowing through the loadpiston orifice increases. This oil goes betweenselector piston (8) and load piston (9). The oilmoves the load piston against springs (10). Thisfurther increases the compression of the springs.As the springs are compressed, the force of thesprings is increased. The pressure of the oil in theclutch is balanced against the force of springs (10).This allows an increase in the oil pressure in theclutch. Clutch oil flows through an orifice in themodulation reduction valve (11). Ball check valve(17) opens and oil flows into the slug chamber atthe left end of the modulation reduction valve.

The pressure in the clutch is now at the maximum.Modulation reduction valve (11) moves to the rightand to the left in order to maintain a constantpressure in passage (13).

The amount of time that is necessary for themaximum pressure in the clutch to be reached isdependent on the size of load piston orifice (15) andthe force of springs (10). The force of springs (10)can be adjusted by using shims in load piston (9).


Shift with a Released Clutch


When a clutch is disengaged, pilot passage (5) isopen in order to drain through the rotary selectorspool. The force of springs (10) moves selectorpiston (8) fully to the right against load pistonbody (18). Passage (16) is now aligned with drainpassage (19). The force of springs (10) moves loadpiston (9) fully to the right against selector piston (8).

Modulation reduction valve (11) is moved fully tothe right by the force of spring (12). In this position,pump oil in passage (6) cannot flow into passage(13). Passage (6) is open to drain passage (14) andthe pressure in the clutch is released. Decay orifice(20) in drain passage (19) controls the amount oftime that is necessary for the clutch pressure torelease.

35Power Train


Torque Converter Lockup Clutch


The operation of the modulating valve for the torqueconverter lockup clutch is identical to the operationof the modulating valves for the clutches in thetransmission planetary. Pilot oil is supplied by thetransmission oil pump. The pilot oil is controlled bythe torque converter lockup solenoid.

The torque converter lockup solenoid is locatedalongside the downshift solenoid and the upshiftsolenoid.

The modulating valve for the torque converterlockup clutch is mounted on the transmissionpressure control valve.

The Power Train Electronic Control Module (PowerTrain ECM) will energize the torque converter lockupclutch solenoid when direct drive is necessary.During direct drive, the engine is mechanicallyconnected to the transmission by the activation ofthe lockup clutch.

When direct drive is not necessary, the torqueconverter lockup clutch solenoid is deactivated. Thepilot oil supply to the modulating valve for the torqueconverter lockup clutch is cut off. The machine willthen be in torque converter drive. The engine willbe hydraulically connected to the transmission.

Engaging the Lockup Clutch

When the Power Train ECM activates the lockupclutch solenoid, pilot oil from the transmission pumpis allowed to flow into pilot oil passage (21).

As pilot oil flows into the pilot oil passage, selectorpiston (22) and load piston (23) are moved to theright against the force of spring (24). Drain passage(25) is blocked. Spring (24) pushes modulationreduction valve (26) against the force of spring(27). As modulation reduction valve (26) movesto the right, drain passage (28) is blocked, andpressurized oil is allowed to flow from passage (6) topassage (29) to the torque converter lockup clutch.

Oil in passage (29) also flows through load pistonorifice (30). This oil goes between selector piston(22) and load piston (23). This moves load piston(23) further to the right.


The pressure of the clutch oil in passage (29)increases after the clutch is full of oil. Some of theoil from passage (29) goes through orifice (31) inmodulation reduction valve (26). This oil opensball check valve (32). The oil then goes into slugchamber (33). This pressure helps the springs pushboth modulation reduction valve (26) and loadpiston (23) back to the left. The oil that is flowingthrough load piston orifice (30) is delivered at a fixedrate. While load piston (3) is controlled by the oilfrom load piston orifice (30), modulation reductionvalve (26) moves up and down. This causes thepressure in the lockup clutch to increase gradually.This gradual increase due to the movement ofthe spool is called modulation. The modulationof modulation reduction valve (26) maintains aconstant pressure in passage (29). When loadpiston (23) goes fully against the stop, modulationstops. The pressure in the lockup clutch is now atthe maximum. The lockup clutch is fully engaged.

The amount of time that is necessary for themaximum pressure in the lockup clutch to bereached is dependent on the size of load pistonorifice (30) and the force of spring (24). The forceof spring (24) can be adjusted by using shims inload piston (23).

Releasing the Lockup Clutch

When pilot oil passage (21) does not receive pilotoil, the force of spring (24) moves selector piston(22) to the left against load piston body (34). Thisuncovers drain passage (25). Oil between selectorpiston (22) and load piston (23) drains throughdrain passage (25).

Passage (35) is now aligned with drain passage(25). The force of spring (24) moves load piston(23) fully against selector piston (22). Modulationreduction valve (26) moves up to the fullest extentas a result of the force of spring (24). In this position,pump oil in passage (6) cannot go into passage(29). Passage (29) is now open to drain passage(28). The pressure in the lockup clutch is released.

Note: Drain passages (25), (28), (19), (14), and (27)are connected. The return oil goes into the torqueconverter sump.

37Power Train


i01540704

Selector and Pressure ControlValve (Transmission)SMCS Code: 3157; 5117


The selector and pressure control valve controls theflow of oil that goes to the pressure control valve.The selector and pressure control valve consists offive valves. The following chart provides the basicfunction of each valve.


Table 3

Operation Of The Components In The SelectorAnd Pressure Control Valve

Valve Function

Priorityreduction valve

(2)This valve controls the pressureof the pilot oil that is available to

rotary selector spool (4).Neutralizervalve (3)

When the transmission is not inNEUTRAL and the engine is started,this valve stops the flow of pilot oil

to rotary selector spool (4).Rotary selector

spool (4)The rotary selector spool sends

pilot oil to the appropriatetransmission clutches.

Relief valve(12)

This valve controls the maximumpressure in the transmission

hydraulic system.

Torqueconverter inletrelief valve (11)

This valve controls the maximum inletoil pressure to the torque converter.

Priority Reduction ValveAt the selector and pressure control valve, the oilfrom the transmission oil pump flows to severallocations. The oil flows through passage (1) topriority reduction valve (2). The oil flows through anorifice in the priority reduction valve. This oil opensa check valve. The oil then flows to the upper endof priority reduction valve (2).

As the oil pressure increases, the priority reductionvalve is moved downward against the force of thespring. The pressure of the oil that is flowing frompriority reduction valve (2) to neutralizer valve (3) iscontrolled by the priority reduction valve.

As priority reduction valve (2) moves downward,pump oil in passage (1) is able to flow throughthrough passage (13). Some of this oil flows to reliefvalve (12). Relief valve (12) controls the maximumpressure in passages (1), (13), and (8). Some ofthe oil from passage (13) flows through passage(8) to the pressure control valve. This oil is usedto fill the clutches in the transmission. Some of theoil from passage (13) also flows to rotary selectorspool (4). This oil activates neutralizer valve (3).When the rotary selector spool is in the NEUTRALposition, oil is able to flow to chamber (14). Thiscauses neutralizer valve (3) to move downward.When neutralizer valve (3) is moved downward, theoil flows into chamber (5) of rotary selector spool(4). Chamber (5) has a screen that filters the oil.This oil is able to flow to the pressure control valve.This pressure oil is the pilot oil that controls themovement of the selector pistons in the pressurecontrol valve.

Neutralizer ValveNeutralizer valve (3) will not allow movement of themachine if the engine is started and rotary selectorspool (4) is not in the NEUTRAL position.

When the engine is started and the transmission isin NEUTRAL, pressure oil from passage (13) flowsto rotary selector spool (4). The pressure oil thenflows to chamber (14). The pressure in chamber(14) moves neutralizer valve (3) downward againstthe force of the spring. This allows pilot oil to goaround the neutralizer valve to chamber (5) of therotary selector spool. The clutches can be engagedin the transmission.

As neutralizer valve (3) moves downward, pilot oilis able to flow through an orifice in the neutralizervalve to the upper end of the neutralizer valve.Neutralizer valve (3) is now held in the open positionby the pressure of the pilot oil.

When rotary selector spool (4) is moved from theNEUTRAL position, pressure oil from passage (13)cannot go to chamber (14). Chamber (14) is nowopen to chamber (6) because of the position ofrotary selector spool (4).

When the machine is not in NEUTRAL and theengine is started, the position of rotary selectorspool (4) stops the flow of pump oil to chamber(14). Neutralizer valve (3) will not move downward inorder to provide oil to chamber (5). No oil can flowto the selector pistons of the pressure control valve.The clutches in the transmission will not engage.

Rotary Selector SpoolRotary selector spool (4) determines the selectorpistons in the pressure control valve that receivepilot oil and the selector pistons that are drained.Orifices in the spool provide the correct sequence inorder for the clutches to engage. A rotary actuatoris mechanically connected to the upper end ofthe rotary selector spool. The rotary actuator ishydraulically controlled by the upshift solenoid andthe downshift solenoid. The rotary actuator turnsrotary selector spool (4). The transmission gearswitch is also connected to the upper end of thespool. The transmission gear switch communicateswith the Power Train Electronic Control Module.Cam (7) is fastened to the lower end of the spool.Springs (9) are in contact with cam (7). The springsprovide detent positions in order to hold the spoolin each selected speed position.

39Power Train


Chamber (5) of rotary selector spool (4) containspilot oil. The position of the spool will send this pilotoil through a passage to the pressure control valve.The oil flows to a selector piston. This causes theselector piston to move. This will cause a clutchto engage in the transmission. Chamber (5) has ascreen which stops foreign material from enteringthe pressure control valve.

The clutches of the transmission that aredisengaged return any pressure oil that is in theselector pistons to chamber (6). Chamber (6) allowsthe oil to go to the transmission case reservoir.

In the NEUTRAL position, rotary selector spool (4)sends pump oil to chamber (14) in order to moveneutralizer valve (3). In the other speed positions,chamber (14) is blocked from pump oil and opento chamber (6).

Relief ValveRelief valve (12) controls the maximum pressure inthe transmission hydraulic system. Pump oil comesfrom passage (13) to relief valve (12). The oil flowsthrough an orifice in the relief valve. This opens apoppet valve. Oil fills the chamber between thepoppet and the slug. As the pressure increases, theoil moves relief valve (12) upward against the forceof the spring. When the pressure of the oil reachesthe relief pressure, relief valve (12) allows oil to flowthrough passage (10) to the torque converter.

The pressure setting of relief valve (12) can bechanged by the removal or the addition of shimsinside the spool of the relief valve.

Torque Converter Inlet Relief ValveTorque converter inlet relief valve (11) controls themaximum oil pressure that is going into the torqueconverter. Oil that flows past relief valve (12) willthen flow to the torque converter. If the pressure ofthe oil reaches the relief pressure, torque converterinlet relief valve (11) will open. The oil will flow tothe transmission case reservoir until the pressure isreduced to less than the maximum pressure that isrequired for the torque converter.


i01541642

Rotary Actuator(Transmission)SMCS Code: 3166


The rotary actuator is controlled by downshiftsolenoid (1) and upshift solenoid (2). Pressure oilfrom either solenoid flows into chamber (3). Thepressure oil presses against stationary vane (12)and against rotary vane (14) of rotor (15). Thispressure oil causes the rotor to turn. Rotor (15) ismechanically connected to the rotary selector spool.The rotary selector spool is part of the selector andpressure control valve. Rotor (15) turns the rotaryselector spool.

During an upshift, pressure oil from the upshiftsolenoid flows through passage (9). This causesupshift valve (10) to move to the left. Drain passage(11) is now closed by the upshift valve. The pressureoil flows into upshift valve (10). This moves ball (8)to the left and oil flows into chamber (13) betweenstationary vane (12) and rotary vane (14). Thiscauses rotor (15) to turn in a clockwise direction.

The oil that is in chamber (3) on the opposite sideof rotary vane (14) presses against downshift valve(4). This causes ball (7) to move to the right side.Oil is then blocked from flowing through passage(6). As the rotor turns, the oil in chamber (3) pushesdownshift valve (4) to the right until the valve opensdrain passage (5). The oil that is in chamber (3) isnow able to drain.

When the rotary selector spool and rotor (15)achieve the correct speed position, the transmissiongear switch that is connected to the rotary selectorspool sends an electrical signal to the Power TrainElectronic Control Module (Power Train ECM). ThePower Train ECM closes the upshift solenoid. Thisstops the flow of pressure oil in passage (9). Themovement of rotor (15) then stops.

During a downshift, pressure oil from the downshiftsolenoid flows through passage (6). Downshift valve(4) is moved to the left. This closes drain passage(5). The pressure oil from passage (6) goes intodownshift valve (4). The pressure oil moves ball (7)to the left and oil flows into chamber (3). This causesrotor (15) to turn in a counterclockwise direction.

41Power Train


The oil that is in chamber (13) presses againstupshift valve (10). This causes ball (8) to move tothe right. This stops oil from going through passage(9). As the rotor turns, the oil in chamber (13)pushes the upshift valve to the right until drainpassage (11) is open to chamber (13).

When the rotor achieves the correct speed position,the Power Train ECM deactivates the downshiftsolenoid. Pressure oil in passage (6) is stopped.This stops the movement of rotor (15).

When the transmission is in the NEUTRAL position,rotor (15) is in the position that is shown. Thedownshift solenoid is always activated in theNEUTRAL position so that the rotor is locked inposition.

42Power TrainTesting and Adjusting Section

Testing and AdjustingSection

Troubleshootingi01526102

Machine Preparation forTroubleshootingSMCS Code: 3000-035

When testing and adjusting the transmission andpower train, move the machine to an area clear ofobstructions, with safe exhaust ventilation for theexhausts. Sudden movement of the machine or re-lease of oil under pressure can cause injury to per-sons on or near the machine. To prevent possibleinjury, do the procedure that follows before testingand adjusting the transmission and power train.

1. Move the machine to a smooth horizontallocation. Move away from any machines that areworking and any personnel.

g00792760Illustration 36Dump body prop

2. Raise the dump body of the truck. Install thedump body prop in order to support the dumpbody.

3. Ensure that the transmission control is in theNEUTRAL position. Move the parking brakecontrol to the ENGAGED position and stop theengine.

4. Permit only one operator on the machine. Eitherkeep other personnel away from the machine, orkeep other personnel in the sight of the operator.

5. Install the steering frame lock. Refer to Operationand Maintenance Manual, SEBU7498.

6. Place blocks in front of the wheels and behindthe wheels.

7. Make sure that all oil pressure is released beforeany fittings, hoses or components are worked on.

8. Push on the brake pedal many times until thereis no brake oil pressure.

Visual checks are the first steps in order totroubleshoot a problem. The visual checks find theproblems that can be quickly corrected. If the visualchecks do not show any problems, the operationalchecks are the next steps. The operational checkspermit the identification of possible problems withthe machine during operation.

i01556822

General TroubleshootingInformationSMCS Code: 3000-035

When you are attempting to define a problem withthe power train, it is necessary to perform theprocedures that are contained in this section.

A visual inspection of the system must be carriedout in order to eliminate many of the less complexproblems.

Upon completion of a visual inspection, if the causeof the problem has not been diagnosed, carry outoperational checks of the system.

If both visual inspection and operational checkshave been carried out and there is still no clearindication of the cause of the problem then it will benecessary to refer to the troubleshooting proceduresand the test procedures that are contained in thismanual.

Troubleshooting a system such as the powertrain is a complex operation. Refer to the varioustroubleshooting sections in this manual for specificroutines for troubleshooting.

43Power Train

Testing and Adjusting Section

This list of possible problems and possiblecorrections will only provide an indication of thelocation of a problem and the repairs that arerequired. It is important to remember that a problemis not necessarily caused by a single part, but bythe relation of one part to a number of other parts.This information cannot provide all the possibleproblems and corrections. It is necessary for servicepersonnel to define the problem. Any repairs maythen be carried out.

i01526104

Visual InspectionSMCS Code: 3000-035

Perform a visual inspection at the beginningof troubleshooting a problem. Ensure that thetransmission control is in the NEUTRAL position.Move the parking brake control to the ENGAGEDposition and stop the engine.

Do not check for leaks with your hands. Pin hole(very small) leaks can result in a high velocity oilstream that will be invisible close to the hose. Thisoil can penetrate the skin and cause personal in-jury. Use cardboard or paper to locate pin holeleaks.

1. Check the oil levels for the various componentsof the power train.

Check the oil level for the torque converterand the transmission. Refer to Operation andMaintenance Manual, SEBU7498, TorqueConverter and Transmission Oil Level - Check.

Check the oil level for the transfer gear. Refer toOperation and Maintenance Manual, SEBU7498,Transfer Gear Oil Level - Check.

Check the oil levels for the differentials and finaldrives. Refer to Operation and MaintenanceManual, SEBU7498, Differential and Final DriveOil Level - Check.

2. Check the level of the coolant in the enginecooling system. Refer to Operation andMaintenance Manual, SEBU7498, CoolingSystem Level - Check.

Note: Engine coolant passes through the oil coolerfor the transmission in order to cool the torqueconverter and the transmission oil.

3. Check for leaks.

Inspect all oil lines, hoses, and connections fordamage or for leaks. Look for oil on the groundunder the machine.

Note: If oil can leak out of a fitting or a connection,air can leak into the system. Air in the system canbe as bad as a low oil level.

4. Check the electrical system.

Inspect the harnesses and the electricalconnectors for the ECM. Refer to ElectricalSchematic, RENR5136.

With the engine start switch and the batterydisconnect switch in the OFF position, checkthe 20 ampere fuse for the Electronic ControlModule. If the fuse is open, replace the fuse.Refer to Operation and Maintenance Manual,SEBU7498, Fuses - Replace.

Inspect the electrical harnesses for damagedwires or for broken wires. Disconnect eachconnector and look for pins and sockets thathave been bent, broken, or removed. Look forany foreign material inside the connectors. Theconnectors must be tightened with normal force.The connectors must be disconnected with thesame amount of force.

Check the Electronic Control Module. Refer toSystems Operation, Troubleshooting, Testing andAdjusting, RENR3442, Power Train ElectronicControl System.

5. Check the batteries.

Turn the battery disconnect switch to the ONposition and check the condition of the batteries.

6. Check the filters and the screens.

Inspect the suction screen for the torqueconverter and the transmission. Clean thesuction screen for the torque converter andthe transmission. Refer to Operation andMaintenance Manual, SEBU7498, TorqueConverter Scavenge Screen - Clean.

Inspect the oil filter for the torque converterand the transmission. Refer to Operation andMaintenance Manual, SEBU7498, TorqueConverter and Transmission Oil Filter - Replacein order to remove the oil filter. Refer to Operationand Maintenance Manual, SEBU7498, Oil Filter- Inspect in order to inspect the oil filter.


Note: The oil filter for the torque converter andthe transmission has a bypass valve which allowsoil to bypass the oil filter elements when the inletpressure to the oil filter rises due to a blockagein the oil filter. Any oil that does not go throughthe filter elements goes directly into the hydrauliccircuit. Dirty oil causes restrictions in valve orifices,sticking valves, etc.

Inspect the oil filter for the transfer gear. Refer toOperation and Maintenance Manual, SEBU7498,Transfer Gear Oil Filter - Replace in order toremove the oil filter. Refer to Operation andMaintenance Manual, SEBU7498, Oil Filter -Inspect in order to inspect the oil filter.

Note: The oil filter for the transfer gear has abypass valve which allows oil to bypass the oil filterelements when the inlet pressure to the oil filterrises due to a blockage in the oil filter. Any oil thatdoes not go through the filter elements goes directlyinto the hydraulic circuit. Dirty oil causes restrictionsin valve orifices, sticking valves, etc. The oil filterfor the transfer gear incorporates a switch, whichilluminates an indicator in the cab. This indicatoralerts the operator of a restriction in the oil filter forthe transfer gear.

Inspect the magnetic screen for the torqueconverter and the transmission. Refer toOperation and Maintenance Manual, SEBU7498,Torque Converter Scavange Screen - Clean.The magnetic screen for the torque converterand the transmission is located within thesuction screen for the torque converter and thetransmission.

Inspect the magnetic screen for the transfer gear.Refer to Operation and Maintenance Manual,SEBU7498, Transfer Gear Magnetic Screen -Clean.

Magnets separate the ferrous particles from thenonferrous particles.

This is a list of some of the particles that may befound in the filter elements:

Aluminum particles give the indication oftorque converter failure or sleeve bearingfailure.

Bronze particles give the indication of sleevebearing failure.

Rubber particles give the indication of rubberseal or hose failure.

Shiny steel particles give the indication ofpump failure.

Iron chips, steel chips or plastic particlesgive the indication of broken components intransmission or transfer gears.

If any contamination is found in the filter elementsor the screens, all the components of thetransmission hydraulic system must be cleaned.Do not use any damaged parts. Any damagedparts must be removed and new Caterpillar partsmust be installed.

i01556743

Operational ChecksSMCS Code: 3000-035

Operate the machine in each direction and inall speeds. Operate the interaxle differential andoperate the axle differentials. Check that the powertrain is operating correctly in all functions. If thepower train is not operating correctly refer to thetroubleshooting information that is contained inthis manual. Use the troubleshooting information inorder to investigate the problem.

The checks for troubleshooting that are includedin this manual are designed to guide servicepersonnel in a correct troubleshooting procedure.The checks and procedures are set in sequence inorder to find problems and causes quickly.

The checks for troubleshooting should be carriedout in order. Do not proceed to the next check untilthe current check has been carried out fully. If thecorrect result for the check is found, go directly tothe next check.

Take note of all warnings and notices in thesechecks. You must read all the warnings and thenotices before you start a check. Before carrying outa procedure, it is important to read the procedurethoroughly.

The checks that follow can be used to find many ofthe problems that may occur during the operationof the machine. The checks that follow can alsogive an indication of the part of the system that hasthe problem.

45Power Train


i01545887

Torque ConverterTroubleshootingSMCS Code: 3101-035

Note: The troubleshooting information is intended toaid in diagnosing a given problem. The possiblecauses are ordered from the most probable causeto the least probable cause. The possible causesshould be examined in order until the problem isresolved.

Refer to Systems Operation, Testing and Adjusting,Machine Preparation for Troubleshootingbefore you perform any testing and adjusting ortroubleshooting.

Prior to carrying out troubleshooting on the torqueconverter, use Caterpillar ET in order to diagnoseany fault codes that may be present. Refer toSystems Operation, Troubleshooting,Testing andAdjusting , RENR3442, Power Train ElectronicControl System.

If fault codes are present, repair the cause of thefault code.

The Torque Converter or theTransmission is OverheatingPossible Cause

1. The machine may have been operatedincorrectly.

Operate the machine in the correct manner.Refer to Operation and Maintenance Manual,SEBU7498.

2. The level of the engine coolant is lower than thespecification.

Check the engine coolant level. Refer toSystems Operation, Testing and Adjusting,Visual Inspection.

3. The power train oil level is lower than thespecification.

Check the power train oil level. Refer toSystems Operation, Testing and Adjusting,Visual Inspection.

4. The engine cooling system and the fan drivesystem may not be functioning correctly.

Refer to Systems Operation, Testing andAdjusting, RENR5126, Hoist, Steering,Suspension, and Fan Drive Systems for furtherinformation regarding the fan drive system.

Refer to Systems Operation, Testing andAdjusting, RENR1362 for more information onthe engines for the 740.

5. There is debris and damaged components inthe power train.

Inspect the oil filter for debris.

Determine the origin of the debris and repairthe damaged component.

Change the oil in the power train and install anew oil filter.

6. The coolant flow through the transmission oilcooler is below the specification.

7. The oil flow through the transmission oil cooler isbelow the specification.

Check the oil pressure to the transmission oilcooler. Refer to Systems Operation, Testingand Adjusting, Power Train Pressures.

8. The inlet relief pressure for the torque convertermay not be within the specification.

Check the inlet relief pressure for the torqueconverter. Refer to Systems Operation, Testingand Adjusting, Power Train Pressures.

Adjust the torque converter inlet relief valve.Refer to Systems Operation, Testing andAdjusting, Transmission Hydraulic Control -Test and Adjust.

9. The torque converter is worn or damaged.

Inspect the components of the torque converterfor wear or damage. Refer to Disassembly andAssembly, RENR5139, Torque Converter -Disassemble and Assemble.

10. The torque converter lockup clutch is notfunctioning correctly.

Test the function of the torque converter lockupclutch. Refer to Systems Operation, Testingand Adjusting, Power Train Pressures.

The Torque Converter LockupClutch Does Not EngagePossible Cause

1. There may be an electrical fault between theECM for the power train and the solenoid for thetorque converter lockup clutch.


Check the wiring and check the connectors fordamage. Refer to Systems Operation, Testingand Adjusting, Visual Inspection.

Repair any damage that is found in the wiringharness or replace any loose connections thatare found.

2. The power train oil level is below the specification.

Check the power train oil level. Refer toSystems Operation, Testing and Adjusting,Visual Inspection.


Inspect the oil filter for debris.



4. The pressure of the oil in the transmissionhydraulic control system may not be within thespecification.

Test the pressures of the oil in the transmissionhydraulic control system. Make anynecessary repairs or adjustments. Refer toSystems Operation, Testing and Adjusting,Transmission Hydraulic Control - Test andAdjust.

5. The solenoid for the torque converter lockupclutch does not function correctly.

Check the operation of the solenoid for thetorque converter lockup clutch before theengine start switch is turned off. Refer toSystems Operation, Testing and Adjusting,Transmission Hydraulic Control - Test andAdjust.

6. The modulating valve for the torque converterlockup clutch may not be functioning correctly.

Check the operation of the modulatingvalve for the torque converter lockup clutch.Systems Operation, Testing and Adjusting,Transmission Hydraulic Control System - Testand Adjust.

7. Components in the torque converter lockupclutch may be worn.

Check the oil pressure in the torque converterlockup clutch. Refer to Systems Operation,Testing and Adjusting, Power Train Pressures- Test.

Check the condition of the piston in the torqueconverter lockup clutch. Refer to Disassemblyand Assembly, RENR5139, Torque Converter- Disassemble and Assemble.

The Torque Converter LockupClutch Does Not Disengage and theEngine Dies at Low SpeedPossible Cause

1. There may be an electrical fault between theECM for the power train and the solenoid for thetorque converter lockup clutch.

Check the wiring and check the connectors fordamage. Refer to Systems Operation, Testingand Adjusting, Visual Inspection.

Repair any damage that is found in the wiringharness or replace any loose connections thatare found.


Inspect the oil filter for debris. Refer to SystemsOperation, Testing and Adjusting, VisualInspection.



3. The solenoid for the torque converter lockupclutch does not function correctly.

Check the operation of the solenoid for thetorque converter lockup clutch before theengine start switch is turned off. Refer toSystems Operation, Testing and Adjusting,Transmission Hydraulic Control - Test andAdjust.

4. The modulating valve for the torque converterlockup clutch may not be functioning correctly.

Check the operation of the modulatingvalve for the torque converter lockup clutch.Systems Operation, Testing and Adjusting,Transmission Hydraulic Control System - Testand Adjust.

47Power Train


5. The piston in the torque converter lockup clutchmay be sticking.

Check the oil pressure in the torque converterlockup clutch. Refer to Systems Operation,Testing and Adjusting, Power Train Pressures- Test.

Check the condition of the piston in the torqueconverter lockup clutch. Refer to Disassemblyand Assembly, RENR3448, Torque Converter- Disassemble and Assemble.

i01554329

Transmission PlanetaryTroubleshootingSMCS Code: 3160-035

Note: The troubleshooting information is given to aidin diagnosing a given problem. The possible causesare ordered from the most probable cause to theleast probable cause. The possible causes shouldbe examined in order until the problem is resolved.

Refer to Systems Operation, Testing and Adjusting,Machine Preparation for Troubleshootingbefore you perform any testing and adjusting ortroubleshooting.

Prior to carrying out troubleshooting on thetransmission planetary group, use CaterpillarET in order to diagnose any fault codes thatmay be present. Refer to Systems Opera

systems operation testing and adjusting cat 740 articulated

Documents

product operation

product damage

repair information

safety alert symbol

safety precautions

safety alert warning

current information

general information