Introduction

Reference: For Specifications with illustrations make reference to SPECIFICATIONS for D35HP and D400 ARTICULATED DUMP TRUCK POWER TRAIN, Form No. HENR8182. If the Specifications in form HENR8182 are different to those given in this book, look at the printing date on the back cover of each book. Use the information given in the book with the latest date.

Power Train Arrangements

Tractor Arrangement

Tractor Power Train Arrangement
1. Output Transfer Drive 2. Transmission 3. Input Transfer Drive 4. Transmission Drive Shaft 5. Torque Converter 6. Engine 7. Front Final Drive 8. Front Differential 9. Front Drive Shaft 10. Center Drive Shaft

A ring gear mounted on the engine flywheel drives the torque converter (5). The torque converter has an integral lock up clutch which allows the machine to operate in converter drive or direct drive. The transmission drive shaft (4) transmits power through the input transfer drive (3) to the transmission (2). The transmission is a full power shift planetary type which contains six hydraulically actuated clutches to provide four forward and four reverse speeds.

The transmission output shaft transmits drive through the output transfer drive (1) to the front and center drive shafts (9 and 10). The front drive shaft is connected to the front differential (8) which transmits torque to the wheel mounted final drives (7). The center drive shaft (10) is connected to the trailer drive line.

D35HP Trailer Arrangement

D35HP Trailer Power Train Arrangement
1. Park Brake and Mid Bearing 2. Drive Shaft 3. Transfer Drive 4. Through Hitch Drive Shaft 5. Center Drive Shaft 6. Drive Shaft 7. Trailer Axle Differential 8. Trailer Axle Final Drive

Drive is transmitted from the tractor by the center drive shaft (5) and through hitch drive shaft (4) to the input side of the transfer drive (3).

The transfer drive transmits drive through drive shafts (2) and (6) and mid bearing (1) to the trailer axle differential (7). The differential transmits drive to the wheel mounted final drives (8).

The tractor inter axle differential transmits more torque to the trailer axle than to the tractor axle. This is to allow for the unequal axle loadings.

D400 6x6 Trailer Arrangement

D400 6x6 Trailer Power Train Arrangement
1. Drive Shaft 2. Mid Bearing 3. Drive Shaft 4. Transfer Drive 5. Center Drive Shaft 6. Through Hitch Drive Shaft 7. Drive Shaft 8. Center Axle Differential 9. Center Axle Final Drives 10. Rear Axle Differential 11. Rear Axle Final Drives

Drive is transmitted by the center drive shaft (5) and through hitch drive shaft (6) to the input side of the transfer drive (4). The transfer drive is connected to the center axle differential (8) by drive shaft (7) and to the rear axle differential (10) by drive shafts (3 & 1). The axle differentials transmit torque to the final drives (9 & 11).

D400 6x4 Trailer Arrangement

D400 6x4 Trailer Power Train Arrangement
1. Rear Drive Shaft 2. Center Drive Shaft 3. Through Hitch Drive Shaft 4. Center Axle Differential 5. Center Axle Final Drives

Drive is transmitted by the center drive shaft (2) and through hitch drive shaft (3) to the rear drive shaft (1). The rear drive shaft is connected to the center axle differential (4). The differential transmits torque to the final drives (5).

Torque Converter

Torque Converter
1. Engine Flywheel 2. Rotating Housing 3. Piston 4. Plate 5. Stator 6. Impeller 7. Drive Gear 8. Port 9. Inlet Passage 10. Outlet Passage 11. Output Shaft 12. Passage 13. Output Yoke 14. Carrier 15. Passage 16. Carrier 17. Hub 18. Turbine 19. Clutch Plates 20. Clutch Discs 21. Clutch Hub 22. Freewheel Assembly 23. Flywheel Pilot 24. Cam

The torque converter is a remote mounted, single stage, rotating housing type. The converter incorporates a lock-up clutch which allows it to be operated in converter drive or in direct drive. Converter drive enables the vehicle to be moved from standstill, provides high output power over a broad speed range, and functions as a shock damper during each gear change.

The drive ring, which is integral with the engine flywheel, is the connecting member between the engine and the torque converter. The internal teeth of the flywheel drive ring engage with the external teeth of the rotating housing (2). The rotating housing is bolted to the impeller (6). The drive gear (7) and impeller (6) are bolted to the hub (17). The engine flywheel, rotating housing, impeller, drive gear and hub turn as a unit at the same speed and in the same direction as the engine crankshaft.

The gear (7) drives the transmission hydraulic pump. The pump draws oil from the output transfer gear case and provides oil under pressure for the torque converter and transmission. Return oil from the torque converter and transmission drains into the output transfer gear case.

Converter Drive

Oil enters the torque converter through inlet passage (9) and flows along internal passages to the impeller (6). The impeller blades pick up inlet oil and direct it against the blades of the turbine (18). The turbine and clutch hub (21) are bolted together and the clutch hub assembly is splined to the converter output shaft (11), which is connected to the output yoke (13). A driveshaft and yoke arrangement transmits drive from the output yoke to the input transfer gears of the transmission.

After oil passes through the turbine, it is redirected to the impeller by the stator (5) to assist in torque amplification. When output torque requirements exceed input torque from the engine, such as when the machine is being accelerated from standstill, the impeller is turning at the same speed as the engine but the turbine is turning relatively slowly. Oil passing through the turbine hits the stator blades so that the stator tends to turn in the opposite direction to the turbine. The stator is prevented from turning by the freewheel assembly (22), which is locked up. The stator then directs most of the oil passing through the turbine back to the impeller. Oil not passing back to the impeller flows out of the converter through passage (12).

Power Flow in Converter Drive

The freewheel assembly is a one way clutch consisting of cam (24), rollers (25), springs (26) and carrier (14). Cam (24) is spline connected to the stator (5) so that when the stator tries to move in the opposite direction to the turbine, rollers (25) are forced into the narrow end of tapered grooves (27), preventing the cam and stator assembly from rotating around the carrier. Since the carrier is held stationary, the stator cannot turn and the freewheel assembly (one way clutch) is locked up.

Detail of Freewheel Assembly
14. Carrier 24. Cam 25. Rollers 26. Springs 27. Grooves

When the output torque requirements are equal to or less than input torque, such as when ground speed is high and the resistance is low, the turbine will be turning relatively quickly. Oil passing through the turbine then strikes the back of the stator blades so that the stator starts to run in the same direction as the turbine. The cam (24) then rotates so that rollers (25) occupy the wide end of grooves (27). The stator asembly is then free to rotate around the carrier (freewheel) and oil passing through the turbine flows out of the torque converter through passage (10).

In converter drive power flow is through the flywheel, rotating housing, impeller, turbine and output shaft.

Direct Drive

The lock up clutch assembly is situated within the rotating housing (2). The internally splined clutch discs (20) are engaged with lock up clutch hub (21) which in turn is splined to output shaft (11) which turns at output speed. The externally splined plates (19) are engaged with the rotating housing (2) which turns at input speed.

Torque Converter in Direct Drive

When the transmission input reaches the required speed (and the oil pressure to the transmission control valve reaches a pre-determined level) a solenoid valve is actuated. Oil is then directed to port (8). This oil flows through passage (15) and down the middle of output shaft (11) to the cavity behind flywheel pilot (23). From here the oil flows through passages in the rotating housing to piston (3) which engages the lock-up clutch. With the lock-up clutch engaged the impeller, turbine and freewheel assembly rotate as a unit. Power flow is through the flywheel, rotating housing, lock-up clutch and converter output shaft.

The lock-up clutch remains engaged for as long as the transmission input speed and main oil pressure remain high enough. If either condition fails to be met the lock-up clutch is disengaged. This condition occurs during gear shifts and the system reverts to converter drive. This action prevents excessive shocks to the power train resulting from the gear shift.

Torque Converter Mounting

Torque Converter Mounting
1. Flywheel Housing 2. Engine Flywheel 3. Adaptor Ring 4. Torque Converter Cover 5. Rotating Housing 6. Drive Gear 7. Transfer Pipe 8. Flywheel Pilot 9. Crankshaft Gear

The engine flywheel assembly (2) is located by a pilot on crankshaft gear (9) and is bolted to the gear. Flywheel pilot (8) locates in the bore of the flywheel to maintain concentricity between the rotating housing (5) and flywheel (2). The torque converter cover (4) is located to the engine flywheel housing (1) by adaptor ring (3).

Oil for lubricating the flywheel and rotating housing is drained from the flywheel housing by transfer pipe (7).

Input Transfer Drive

Input Transfer Drive
1. Shims 2. Drive Gear 3. Bearing 4. Driven Gear 5. Bearing 6. Shims 7. Gasket 8. Cover Plate 9. Bearing 10. Seal 11. Yoke 12. Seal 13. Bearing

Drive is transmitted from the converter output shaft, through the transmission drive shaft to yoke (11). The yoke is spline connected to drive gear (2) which is engaged with driven gear (4). The driven gear is spline connected to the transmission input shaft.

Shims (1) are provided to adjust the end float in the bearings (3 & 13) which support the drive gear (2). Shims (6) are provided to adjust the end float in the bearings (5 and 9) which support the driven gear.

Planetary Transmission

Planetary Transmission
1. No.1 Clutch Ring Gear 2. No.1 Clutch 3. No.2 Clutch 4. No.2 Clutch Ring Gear 5. No.2 Sun Gear 6. No.3 Clutch 7. No.3 Clutch Ring Gear 8. No.4 Clutch 9. No.3 Carrier 10. No.5 Clutch 11. No.6 Clutch 12. No.6 Clutch Ring Gear 13. Gear 14. No.4 Carrier and Output Shaft 15. No.5 Clutch Housing and Shaft 16. No.6 Planetary Gears 17. No.5 Clutch Ring Gear 18. No.4 Clutch Ring Gear 19. No.4 Planetary Gears 20. Gear 21. No.3 Planetary Gears 22. No.2 Planetary Gears 23. No.3 Sun Gear and Shaft 24. No.2 Carrier 25. No.1 Planetary Gears 26. Input Shaft 27. No.1 Sun Gear 28. No.1 Carrier 29. Ring Gear

The directional section of the transmission consists of No.1 and No.2 clutches and the associated planetary arrangement. No.2 clutch (3) is the forward directional clutch and No.1 clutch (2) is the reverse directional clutch. No.1 sun gear (27) and No.2 sun gear (5) are spline connected to input shaft (26) which is driven from the torque converter and input transfer drive.

The speed section of the transmission consists of No.3, No.4, No.5 and No.6 clutches and the associated planetary arrangement. No.6 clutch (11) gives first speed, No.5 clutch (10) gives second speed, No.4 clutch (8) gives third speed and No.3 clutch (6) gives fourth speed. The No.4 carrier and output shaft (14) is splined to the drive gear in the output transfer drive.

Forward Drive

In forward drive No.2 clutch (3) is engaged. No.2 sun gear (5) is engaged with planetary gears (22). No.2 clutch (3) is engaged so that ring gear (4) is held stationary forcing the planet carrier (24) to rotate. Rotation of sun gear (27) is transmitted to planetary gears (25) which in turn are engaged with ring gear (29). Ring gear (29) is connected to the driven planet carrier (24) but because No.1 clutch (2) is disengaged this motion is lost because planet gears (25) are free to rotate about their own axes. The rotating planet carrier (24) provides forward motion.

Reverse Drive

In reverse drive No.1 clutch (2) is engaged. Ring gear (1) is spline connected to carrier (28) so that both are held stationary by the engaged clutch. No.1 sun gear (27) is engaged with planetary gear (25), forcing them to rotate about their own axes. These planetary gears are engaged with ring gear (29) which is splined to No.2 carrier (24). Ring gear (29) therefore acts as an idler providing reverse rotation of carrier (24).

Rotation of sun gear (5) is transmitted to planet gears (22) but this motion is lost through the disengaged No.2 clutch.

First Speed

In first speed No.4 carrier and output shaft (14) resists rotation due to the inertia of the drive line on the output side of the transmission. Ring gear (12) is held stationary by the engaged No.6 clutch (11). Planet carrier (24) is driven due to No.2 clutch (FORWARD) or No.1 clutch (REVERSE) being engaged.

Driven planet carrier (24) carries No.3 planetary gears (21) which are engaged with No.3 sun gear and shaft (23) and ring gear (7). No.3 sun gear and shaft is connected to output shaft (14) and therefore resists rotation due to inertia. Thus drive from planetary gears (21) is transmitted to ring gear (7) which is connected to No.3 carrier (9). Carrier (9) holds No.4 planetary gears (19) which are engaged with gear (20) and ring gear (18). Gear (20) is connected to No.3 sun gear and output shaft (23) and therefore resists rotation due to inertia. Therefore drive is transmitted through ring gear (18) to No.5 clutch housing and shaft (15). No.5 clutch housing and shaft carries gear (13) which is engaged with No.6 planetary gears (16). Since ring gear (12) is held stationary drive is transmitted to No.4 carrier and output shaft (14).

Second Speed

In second speed No.5 clutch (10) is engaged. The assembly consisting of No.5 clutch housing and shaft (15), gear (13) and ring gear (18) and the assembly consisting of No.4 carrier and output shaft (14), No.3 sun gear and shaft (23), gear (20) and ring gear (17) are then locked together by the engaged clutch. No.5 clutch is the only clutch that rotates. No.3 planetary gears (21) are engaged with ring gear (7) and No.3 sun gear and shaft (23). Ring gear (7) is splined to No.3 carrier (9). No.3 carrier holds No.4 planetary gears (19) which are engaged with gear (20) and ring gear (18). Gear (20) and ring gear (18) are locked together by the engaged No.5 clutch. Thus drive is transmitted from the rotating planet carrier (24) to the output shaft (14) through No.3 sun gear and shaft (23) and ring gear (7).

Third Speed

No.4 clutch (8) is engaged preventing rotation of ring gear (18). No.5 clutch housing and shaft (15) is attached to ring gear (18) and gear (13) is attached to No.5 clutch housing and shaft (15). Therefore, clutch housing and shaft (15) and gear (13) must also remain stationary.

Rotating carrier (24) has No.3 planetary gears (21) meshing with ring gear (7) which is attached to carrier (9). Carrier (9) has planet gears (19) meshing with gear (20) and ring gear (18). Since ring gear (18) is stationary rotation of planet gears (19) causes rotation of gear (20). No.3 planetary gears (21) are also meshed with No.3 sun gear and shaft (23) which is attached to gear (20). Thus drive goes partly from No.3 planetary gears (21) to No.3 sun gear and shaft (23) and partly from No.3 planetary gears (21) through ring gear (7), carrier (9), planetary gears (19) and gear (20) to No.3 sun gear and shaft (23). No.3 sun gear and shaft (23) is attached to No.4 carrier and output shaft (14).

Fourth Speed

No.3 clutch (6) is engaged, therefore ring gear (7) is stationary. Planet gears (21) are forced to rotate about their own axes and thus transmit drive to No.3 sun gear and shaft (23). No.3 sun gear and shaft (23) is spline connected to No.4 carrier and output shaft (14).

Output Transfer Drive (Early Type)

Output Transfer Drive (Early Type)
1. Gear 2. Gear 3. Gear 4. Shaft 5. Housing 6. Gear 7. Input Boss 8. Casing

Output Transfer Drives

The transmission No.4 carrier and output shaft is spline connected to the input boss (8). The input boss is bolted and dowelled to gear (1). Gear (1) transmits drive to gear (2).

Gear (2) is bolted and dowelled to gear (6), which transmits drive to gear (3). Gear (3) is fixed to housing assembly (5).

Splined shaft (4) passes through the housing. As the housing assembly (5) turns it drives the splined shaft which transmits drive to the front axle differential and to the trailer drive line.

The assemblies consisting of input boss (7)/gear (1), gear (2)/gear (6) and gear (3)/housing (5) are carried in taper roller bearings. The end float in these assemblies is adjustable with shims.

The later output transfer drive arrangement is similar to the early arrangement except that the housing assembly (5) is replaced with a one piece carrier and the single splined shaft (4) is replaced by two shafts.

Output Transfer Drive (Later Type)

Output Transfer Drive (Later Type)
1. Gear 2. Gear 3. Gear 4. Shaft 5. Carrier 6.Shaft 7. Gear 8. Input Boss 9. Casing

Standard Differential

Differential
1. Input Shaft 2. Differential Case 3. Bevel Gears (four) 4. Bevel Gear 5. Spider 6. Output Gears (two)

The purpose of the differential is to transmit equal torque to the two wheels. When one wheel needs to turn slower than the other (such as during a turn or when one wheel is passing over an obstacle) the differential allows the inside wheel to slow down in relation to the outside wheel while maintaining an equal torque split between the wheels.

A yoke is fastened to the splined end of the differential input shaft(1) and is driven by a drive shaft. The differential case(2) is bolted to bevel gear(4) and carries a spider(5). The spider carries four bevel gears(3) which mesh with the two output gears(6). The output gears are spline connected to the axle shafts.

Drive is transmitted from the drive shaft to input shaft(1) and bevel gear(4). As the bevel gear(4) and case(2) rotate, the spider(5) and bevel gears(3) rotate, thus driving the output gears and axle shafts.

When the truck is being driven straight ahead with equal traction under each wheel the torque transmitted to each wheel is the same. The case(2), spider(5) and bevel gears(3) will then rotate as a solid mass and drive the axle shafts. The bevel gears will not rotate on spider (5).

When a turn is made unequal forces are exerted on the wheels. A greater force is exerted on the inside wheel than the outside wheel. Since the wheels are connected to the output gears(6) through the axle shafts and final drives, the forces acting on the output gears are unequal. This causes the bevel gears(3) to rotate on spider(5) allowing the output gear driving the inside wheel to slow down and causing the output gear driving the outside wheel to speed up.

If the traction under one wheel is reduced the torque required to drive that wheel is reduced. Therefore the torque transmitted to the opposite wheel is also reduced. If the traction under one wheel is lost the torque required to turn that wheel will be virtually zero. The output gear and axle shaft are rotating against zero resistance so that their speed will increase and the wheel will spin. Drive will be in the direction of least resistance (toward the spinning wheel) so that the bevel gears (3) will rotate on spider (5) and "walk" around the opposite output gear, thus transmitting no torque to that wheel.

No-Spin Differential(An Attachment)

No-Spin Differential
1. Input Shaft 2. Output Gears 3. Bevel Gear 4. Differential Assembly 5. Spider 6. Differential Case.

The purpose of a NoSPIN differential is to allow one wheel to turn faster than the other during a turn, or when travelling over rough ground, but at the same time prevent wheel-spin when one wheel loses traction.

The input shaft(1) drives bevel gear(3) and differential case(6). The differential case houses the spider(5), which is part of the NoSPIN differential assembly(4). The axle shafts mesh with internal splines in the differential output gears(2).

When both wheels are required to turn at the same speed (such as when the machine is being driven straight over a smooth surface) the differential is locked and equal torque is transmitted to each wheel. When the machine is being turned, or when one wheel is going over an obstacle, the wheel which needs to turn faster is disengaged from the drive line and torque is transmitted to the slower turning wheel only. The machine is powered through the turn by the inside wheel while the outside wheel "freewheels".

No Spin Differential
1. Output Gear 5. Spider 8. Center Cam 9. Holdout Ring 10. Cam 11. Snap Ring 12. Clutch 13. Spring Retainer 14. Cam 15. Spring 16. Holdout Ring Teeth.

The main components of the NoSPIN differential are the spider(5), two springs(15), two output gears (2), two clutches(12), holdout rings(9), center cam(8), snap ring(11) and spring retainers(13). The output gears bear against the differential case(6) so that a pre-load is induced in the springs(15) by retainers(13), thus holding the clutches in engagement with the spider. The spider is mounted in the differential case(6) and therefore turns at the same speed as the bevel gear(3).

The center cam(8) is mounted inside the spider and is held in place by snap ring(11). A spider key fits into a notch in the center cam so that the cam turns with the spider. External teeth in the center cam engage with teeth on cams(14) which are integral with the clutches(12).

The holdout rings(9) fit into annular grooves in the clutches(12). Teeth(16) in the holdout ring engage with grooves in the center cam and the same spider key which drives the center cam also locates into notches in the holdout rings when one of the clutches is disengaged.

The differential case(6) is driven by bevel gear (3) and the spider (5) turns with the case. Since the center cam (8) is connected to the spider by the spider key, the center cam also rotates. In turn the centre cam drives holdout ring (9). The spider (5) drives the clutches (12) which in turn drive the output gears and axle shafts. In this way torque is divided equally between the wheels.

When a turn is made the outside wheel needs to turn faster than the inside wheel but this cannot happen as long as the two clutches are engaged. As the turn is made the forces exerted by the steering action act is such a way that the outside wheel must either speed up or skid. The profiles of the engaging teeth of the center cam (8) and integral cams (14) are shaped so that the integral cam teeth can ride up the center cam teeth.

This camming action disengages the clutch connected to the outside wheel from the spider. Thus the outside wheel is not driven and can speed up as necessary.

As the clutch disengages it pulls holdout ring (9) outward so that the holdout ring teeth disengage from their mating grooves in the center cam. Friction between the holdout ring and clutch groove carries the holdout ring round until the spider key contacts the notch in the holdout ring. The holdout ring and center cam are then both driven at the same speed as the spider but the holdout ring is positioned such that it cannot engage with the center cam. Thus the holdout ring prevents the clutch from engaging with the spider and the outside wheel can turn freely. As the machine is brought into the straight ahead position again the disengaged wheel slows to the same speed as the driven wheel. The ground resistance encountered by the free wheel will exert a slightly negative torque on that wheel. The disengaged clutch will slow down in relation to the spider and friction between the clutch and holdout ring drags the holdout ring back into a position where it can engage with the center cam. When this happens the clutch engages with the spider due to the effect of spring (15) and torque is again divided between the two wheels.

If traction is lost under one wheel the two clutches hold the wheels in a locked condition. Therefore, torque will continue to be transmitted to the wheel with good traction.

Final Drives

Front Final Drive
1. Wheel Assembly 2. Ring Gear 3. Hub 4. Sun Gear 5. Axle Shaft 6. Planet Gears 7. Carrier 8. Spindle

Rear Final Drive
1. Wheel Assembly 2. Ring Gear 3. Hub 4. Sun Gear 5. Axle Shaft 6. Planet Gears 7. Carrier 8. Spindle

The final drives are planetary gear arrangements. The ring gear (2) is mounted on the final drive hub (3) which is spline connected to the spindle(8). The spindle is bolted to the axle housing. Thus the final drive ring gear is held stationary.

Planet gears(6) are mounted on carrier(7) which is bolted to the wheel assembly(1). The sun gear(4) is spline connected to the axle shaft (5) which is connected to the differential at its other end.

The differential drives the sun gear and axle shaft. As the sun gear(4) rotates the planet gears(6) and carrier(8) are forced to rotate by the stationary ring gear(2) in the same direction as the sun gear but at a reduced speed. The rotation of the carrier causes rotation of the wheel assembly(1) which is connected to the rim and tire.

D400 Rear Transfer Drive

D400 Rear Transfer Drive
1. Input Yoke 2. Hitch Tube 3. Shaft 4. Driven Gear 5. Output Yoke 6. Idler Gear 7. Output Yoke 8. Drive Gear 9. Bearing Carrier 10. Bearing Housing 11. Drive Shaft

Drive is transmitted from the center drive shaft to the through hitch drive shaft(11), which has input yoke(1) splined to one end and output yoke(7) splined to the other. Output yoke(7) is connected to the center axle differential by a drive shaft assembly. The through hitch drive shaft carries gear(8) which drives gear(4) through idler(6). Gear(4) is splined to shaft(3) which carries yoke(5). The yoke is connected to the rear axle differential by two drive shaft and yoke assemblies. The overall ratio of the transfer drive is 1:1.

The transfer drive has bearing carrier(9) bolted to it and the assembly is mounted in bearing housing(10). This allows the machine to oscillate.

D35HP Transfer Drive

D35HP Transfer Drive
1. Input Yoke 2. Hitch Tube 3. Shaft 4. Drive Gear 5. Output Yoke 6. Drive Gear 7. Bearing Carrier 8. Bearing Housing 9. Drive Shaft

Drive is transmitted from the center drive shaft to the through hitch drive shaft(9) which has input yoke(1) splined to one end and drive gear(6) splined to the other. Gear(6) drives gear(4) which is splined to shaft(3). Shaft(3) carries yoke(5).

The yoke is connected to the rear axle differential by two drive shaft and yoke assemblies. The gear ratio of the transfer drive is 1.3:1 to synchronize the speeds of the two axles.

The transfer drive has bearing carrier(7) bolted to it and the assembly is mounted in bearing housing(8). This allows the machine to oscillate.

Gearshift Mechanism with Downshift Inhibitor

Downshift Inhibitor (Early Machines)
1. Speed Selector Lever 2. Direction Selector Lever 3. Brake Disc 4. One Way Clutch 5. Plate 6. Sleeve 7. Piston Rod 8. Cylinder 9. Shaft Assembly 10. Cam 11. Follower

The downshift inhibitor arrangement is provided to prevent the operator from making a downward shift when the torque converter is locked up. Downward shifting during torque converter lock up can result in engine overspeed. Upshifts can still be made in the normal way.

When the torque converter is locked up pressurised oil is fed to cylinder (8). Piston rod (7) and sleeve (6) move to the right until brake disc (3) is clamped between sleeve (6) and plate (5). The roller clutch (4) is a one way clutch which allows shaft (9) to rotate in one direction (to make an upshift) but prevents rotation in the other direction (to make a downshift). When the torque converter comes out of lock up, pressure is exhausted from the actuating cylinder and sleeve (6) moves to the left. Brake disc (3) is then free to rotate which overcomes the effect of the one way clutch. Gear shifts can then be made normally. Speed selector lever (1) is held in the selected position by a spring loaded cam (10) which acts against follower (11).

NOTE: In an emergency the downshift inhibitor can be overridden by using excessive force on the gear lever. This action may result in severe engine overspeed and possible mechanical damage.

Gearshift Mechanism with Downshift Inhibitor and Pre-select

Downshift Inhibitor and Pre-select Mechanism (Later Machines)
1. Gear Selector Lever 2. Spring 3. Direction Selector Lever 4. Pivot Arm 5. Shaft 6. Brake Disc 7. Plate 8. One Way Clutch 9. Sleeve 10. Cylinder 11. Arm Assembly

The gearshift mechanism on later machines includes a downshift inhibitor and pre-select arrangement to allow the driver to select the next downward gear while the torque converter is locked up. Although the next gear can be selected the transmission does not actually make the shift until the torque converter comes out of lock-up. Upshifts can be made in the normal way.

When the torque converter is locked up pressurised oil is fed to cylinder (10). Sleeve (9) then moves until brake disc (6) is clamped between the sleeve and plate (7). The roller clutch (8) is a one way clutch which allows shaft (5) to rotate in one direction (to make an upshift) but prevents rotation in the other direction (to make a downshift). If the driver moves the speed selector lever to the next position down pivot arm (4) compresses spring (2) against the face of arm assembly (11). The arm is clamped to shaft (5). Since the shaft is clamped, arm (11) is fixed and the spring is compressed. Thus, although the driver has selected the next speed down the shift has not been made.

When the torque converter comes out of lock up, pressure is exhausted from the actuating cylinder and the clamping force on disc (6) is released. The brake disc is then free to rotate which overcomes the effect of the one way clutch and gear shifts can be made normally. If the driver has previously selected the next downward gear then spring (2) will be compressed when the torque converter comes out of lock up. The preload in the spring will cause arm (11) and shaft (5) to rotate and the gearshift is made.

Power Train Hydraulic System

Power Train Hydraulic Lines (Early Arrangement)
1. Downshift Inhibitor Cylinder 2. Test Point (Lock up Pressure) 3. Test Point (Pump/Speed Clutch Pressure) 4. Pressure Switch 5. Valve Sub-Plate 6. Pressure Reducing Valve 7. Solenoid Valve 8. Filter 9. Transmission Hydraulic Control Valve 10. Oil Cooler 11. Return Pipe 12. Pump Prime Orifice 13. Hydraulic Pump 14. Magnetic Strainer 15. Torque Converter Outlet Relief Valve

The transmission hydraulic pump (13) is driven by a gear bolted to the torque converter impeller. The pump is therefore driven as long as the engine is running. The pump draws oil from the output transfer gear case through magnetic screen (14). This oil is directed through the full flow filter (8) to the main transmission hydraulic control valve (9). Pressure switch (4) is a normally open switch which closes when the oil pressure reaches a certain value. This condition must be met to initiate the lockup clutch engagement sequence.

The transmission hydraulic control valve (9) directs oil at main system pressure to valve sub plate (5) which carries pressure reducing valve (6) and solenoid valve (7). Oil enters the sub plate at port (P) and flows to the pressure reducing valve, which lowers the pressure to the value required for torque converter lock up clutch operation. The pressure reducing valve directs oil at reduced pressure to the solenoid valve (7). When the solenoid valve is energised it directs oil back through sub plate port (B), which is connected to the lock up clutch inlet port (X). The lock up clutch is then engaged. When the solenoid valve is de-energised port (B) is connected to port (T). Oil in the lock up clutch flows back to the transfer gear case and the clutch is disengaged.

Power Train Hydraulic Lines (Later Arrangement)
1. Downshift Inhibitor Cylinder 2. Test Point (Lock up Pressure) 3. Test Point (Pump/Speed Clutch Pressure) 4. Pressure Switch 5. Valve Sub-Plate 6. Pressure Reducing Valve 7. Solenoid Valve 8. Filter 9. Transmission Hydraulic Control Valve 10. Oil Cooler 11. Return Pipe 12. Pump Prime Orifice 13. Hydraulic Pump 14. Magnetic Strainer 15. Torque Converter Outlet Relief Valve

Lock up clutch oil also flows to pressure test point (2) and downshift inhibitor cylinder (1). When the lock up clutch is engaged the downshift inhibitor is activated. This prevents the operator from engaging a lower gear and therefore prevents the possibility of engine overspeed.

The transmission hydraulic control valve also reduces the main oil pressure to the value required for torque converter operation and controls the flow of oil to the transmission clutch packs. Oil enters the torque converter at port (Y) and flows along internal passages to the torque converter impeller. Outlet oil from the torque converter flows along internal passages to converter outlet relief valve (15). The outlet relief valve controls the pressure in the torque converter. Outlet oil from the valve flows through oil cooler (10) to the top of the output transfer drive case. This oil cascades down the output transfer drive to lubricate the gears and bearings and collects in the bottom of the casing. All low pressure oil returning from the transmission hydraulic controls flows to the output transfer drive case.

Internal leakage collecting in the bottom of the torque converter is gravity fed back to the output transfer gear case through pipe (11).

The pump prime orifice is provided to vent air from the pressure side of the pump on initial start up. This assists the pump to prime itself. A very small amount of oil is lost through this orifice during normal running. This oil flows back to the transfer gear case by way of outlet relief valve (15) and cooler (10).

Transmission Hydraulic Pump

The pump assembly is bolted to the rear of the torque converter.

The pump draws oil from the output transfer gear case. This oil is delivered to the transmission hydraulic controls.

Magnetic Screen

Magnetic Screen
1. Magnets and Tube Assembly 2. Screen

The magnetic screen is located in the pump suction line. Oil from the output transfer drive case flows through screen (2), past magnets and tube assembly (1) and out again. The screen removes larger particles of foreign material while any tiny particles of ferrous material which pass through the screen are stopped by the magnets.

Oil Filter

Oil Filter
1. By-pass Valve 2. Spring 3. Plug 4. Inlet Port 5. Base 6. Housing 7. Plug 8. Element 9. Outlet Passage

Normally oil enters the filter through inlet passage (4) and passes through element (8) before flowing through outlet port (9). The filter element removes debris from the oil before it passes through outlet (9) to the main transmission hydraulic control valve.

If the element becomes blocked the restriction to flow will cause a pressure build up on the outside of the element. This increased pressure is felt by by-pass valve (1) which moves to the right against the effect of spring (2). Inlet port (4) is then connected directly to outlet port (9) allowing unfiltered oil to pass to the transmission control valve.

The filter element should normally be replaced every 500 service meter hours to ensure a clean supply of oil to the transmission.

Transmission Hydraulic Control Valve

Transmission Hydraulic Control Valve
1. Speed Selector Spool 2. Load Piston 3. Modulation Relief Valve 4. Pressure Differential/Safety Valve 5. Torque Converter Inlet Pressure Valve 6. Directional Selector Spool 7. Flow Control Orifice 8. Neutralizer Valve (not used) C1.No.1 Clutch (Reverse) C2.No.2 Clutch (Forward) C3.No.3 Clutch (Fourth Speed) C4.No.4 Clutch (Third Speed) C5.No.5 Clutch (Second Speed) C6.No.6 Clutch (First Speed)

The main components of the transmission hydraulic control valve group are:

(1). Speed Selector Spool - controls the flow of oil to and from the speed clutches.

(2). Load piston - controls the rate of pressure increase in the speed clutches in conjunction with the modulation relief valve (3).

(3). Modulation Relief Valve - controls the maximum pressure in the system. Also controls the rate of pressure increase in the speed clutches in conjunction with load piston (2).

(4). Pressure Differential/Safety Valve - maintains a pressure differential between the speed and directional clutches. Also prevents a directional clutch from filling if the machine is started in either forward or reverse.

(5). Torque Converter Inlet Pressure Valve - controls the maximum pressure of the torque converter inlet oil.

(6). Directional Selector Spool - controls the flow of oil to and from the directional clutches.

The transmission neutralizer valve (8) is not used in this application.

On initial start up with the transmission in neutral pump oil flows through the flow control orifice (7) to No.3 clutch, converter inlet valve (5) and pressure differential/safety valve (4). The right hand end of the pressure differential/safety valve is open to tank. Clutch Nos. 1, 2, 4, 5 and 6 are all connected to tank. The right hand end of load piston (2) is also connected to tank.

Engine Running, Transmission in Neutral

Hydraulic Control Valve - Engine Running, Transmission in Neutral
1. Speed Selector Spool 2. Load Piston 3. Modulation Relief Valve 4. Pressure Differential/Safety Valve 5. Torque Converter Inlet Pressure Valve 6. Directional Selector Spool 7. Flow Control Orifice 8. Neutraliser Valve (not used) 9. Orifice

The position of the directional selector spool (6) allows oil to flow to No.3 clutch, converter inlet valve (5) and pressure differential/safety valve (4). Oil flows through an orifice in the converter inlet valve spool and fills the slug chamber at the right hand end of the spool. Oil also flows through an orifice in the spool of the pressure differential/safety valve to fill the chamber at the left hand end of the spool. As the pressure in the chamber at the left hand end of the pressure differential/safety valve increases the spool moves fully to the right against the end cover. This allows oil to flow past the spool to the directional clutch circuit and to fill the spring chamber at the right hand end of the spool. As the directional clutch pressure increases the spool moves back to the left until flow past the spool is stopped. In this position the pressure in the chamber at the left hand end of the spool is balanced by the combined effect of the pressure in the spring chamber and the springs themselves. The valve spool is in a balance position to maintain a constant pressure in the directional clutch circuit. The oil pressure in the directional clutch circuit is lower than in the speed clutch circuit due to the effect of the springs.

Pump oil is also directed to the modulation relief valve (3). This oil flows around the valve spool and through an orifice to act against the integral poppet valve. The poppet valve unseats allowing oil to fill the slug chamber in the spool. At the same time oil flows through an orifice to the right hand end of load piston (2). The position of pressure differential/safety valve (4) blocks the tank passage allowing pressure to build up against the face of the load piston.

When No.3 clutch is full of oil the speed clutch pressure starts to rise. The increasing pressure is transmitted to the slug chamber of the modulation relief valve (3). This moves the modulation relief valve to the right allowing excess flow to pass into the torque converter. Increasing speed clutch pressure is also transmitted to the right hand end of load piston (2) which moves the load piston to the left. This increases the resistance to movement of the modulation relief valve and thus allows the pressure in clutch No.3 to increase further. This gradual increase in pressure is known as modulation and prevents shock loading of the transmission by allowing the clutches to pick up the load gradually. Eventually the load piston moves so far to the left that the chamber at the right hand end is opened to tank. Movement of the load piston then stops and the piston is held in a balanced position. The modulation relief valve also takes up a balance position with excess oil flowing to the torque converter.

Engine Started with Transmission not in Neutral

Engine Started with Transmission not in Neutral
1. Speed Selector Spool 2. Load Piston 3. Modulation Relief Valve 4. Pressure Differential/Safety Valve. 5. Torque Converter Inlet Pressure Valve 6. Directional Selector Spool 7. Flow Control Orifice 8. Neutraliser Valve (not used) 9. Orifice.

If the engine is started with the transmission in either forward or reverse the operation of the pressure differential/safety valve (4) prevents either directional clutch from engaging and thus prevents movement of the machine.

Before the engine is started the pressure differential/safety valve (4) is pushed fully to the left by spring force. If the directional selector spool (6) is in forward or reverse the chamber at the left hand end of the pressure differential/safety valve is connected to tank by orifice (9). If the engine is started pressure is prevented from building up in the chamber and thus prevents the valve from moving to the right. This movement is necessary to initiate the build up of pressure in the directional clutch circuit.

When the directional selector spool (6) is moved to neutral the tank passage is blocked by the spool. Pressure then builds up in the chamber at the left hand end of the spool and the spool moves to the right, covering orifice (9). Once the orifice is covered the chamber is no longer connected to tank, regardless of the position of the directional selector spool. This prevents the pressure in the directional clutch circuit from being dumped to tank every time the selector spool passes through neutral.

First Speed Forward

First Speed Forward
1. Speed Selector Spool 2. Load Piston 3. Modulation Relief Valve 4. Pressure Differential/Safety Valve 5. Torque Converter Inlet Pressure Valve 6. Directional Selector Spool 7. Flow Control Orifice 8. Neutraliser Valve (not used) 9. Orifice.

When first speed forward is selected directional selector spool (6) opens a passage to No. 2 clutch and connects No. 1 clutch and No. 3 clutch to tank. The speed selector spool (1) opens a passage to No. 6 clutch and connects No. 4 clutch and No. 5 clutch to tank.

When the directional selector spool is moved to the forward position (or reverse) pump oil flows through flow control orifice (7), past the spool to the speed selector spool (1). The pressure in the system falls instantaneously as the passage leading from the directional selector spool to the speed selector spool fills. Thus spring force moves modulation relief valve (3) and pressure differential/safety valve (4) to the left. As the pressure differential/safety valve moves to the left the chamber at the right hand end of load piston (2) is opened to tank. Spring force then moves the load piston to the right. The directional clutch pressure is lowered in this way each time a shift is made. This ensures that the speed clutch fills first and that the load is therefore picked up by the directional clutch.

The position of the directional selector spool (6) allows oil to flow to No. 6 clutch, torque converter inlet valve (5) and pressure differential/safety valve (4). Oil flows through an orifice in the spool of the pressure differential/safety valve and fills the chamber at the left hand end of the spool. Increasing pressure in No. 6 clutch is felt in this chamber and when the pressure reaches a certain value the pressure differential/safety valve moves to the right. This allows oil to flow past the spool to No. 2 clutch and into the spring chamber at the right hand end of the spool. As the pressure in No. 2 clutch increases the pressure in the spring chamber also increases. Thus the spool moves back to the left. This action carries on until the speed and directional clutch pressures reach their maximum values. The pressures rise at the same rate but the speed clutch pressure is always higher than the directional clutch pressure.

Pump oil also flows to modulation relief valve (3) and fills the slug chamber at the left hand end. As the speed clutch pressure rises the modulation relief valve moves to the right and load piston (2) moves to the left. The speed clutch pressure gradually increases until the load piston moves so far to the left that the chamber at the right hand end is opened to tank. Movement then stops and the piston is held in a balanced position. The modulation relief valve also takes up a balance position with excess oil flowing to the torque converter.

Torque converter inlet pressure is felt against the left hand end of the valve (5). Speed clutch pressure is transmitted to the slug chamber of the valve. If the converter inlet pressure is high enough to overcome the speed clutch pressure and springs, the valve moves to the right and excess converter inlet pressure is relieved to tank.

Pressure Reducing Valve/Solenoid Valve Group

Schematic Representation

Pressure Reducing Valve/Solenoid Valve Group
1. Solenoid Valve 2. Sub Plate 3. Pressure Reducing Valve

Oil at pump delivery pressure enters the sub plate (3) and is directed through internal passages to the pressure reducing valve (2). The pressure reducing valve is set to reduce the delivery pressure to the value required for lock up clutch operation. Oil at reduced pressure (lock up clutch pressure) is directed to solenoid valve (1).

When the solenoid valve is de-energised oil at lock up clutch pressure is directed through the valve and to the blocked port A in the sub plate by way of internal passages. Since there is no demand for flow from the lock up clutch, oil entering the valve group through port P will be directed to tank through port T by the pressure reducing valve. This oil flows back to the output transfer drive case where it is used to lubricate the gears and bearings. The pressure in the passages leading to port A will be maintained at the value required for lock up clutch operation.

When the solenoid valve is energised oil at lock up pressure flows through the valve to the lock up clutch by way of sub plate port B. The torque converter is then in direct drive. Once the lock up clutch is fully engaged there will be no flow through port B and oil entering at port P will again be directed through port T to lubricate the output transfer gears. When the solenoid is subequently de-energised oil in the lock up clutch returns through port T and the torque converter reverts to converter drive.

Pressure Reducing Valve

Pressure Reducing Valve
1. Spool 2. Passage 3. Passage 4. Passage 5. Port (controlled pressure) 6. Port (inlet pressure) 7. Spring 8. Jam Nut 9. Adjusting Screw

Oil from the transmission hydraulic control valve is directed to port (6) by way of the valve group sub plate. This oil flows past spool (1) to port (5) and through passages (4), (3) and (2) to the right hand end of the spool. Increasing pressure on the end of the spool causes it to move to the left against the effect of spring (7). Eventually the spool blocks the connection between ports (5) and (6). Oil in port (6) then flows through the valve to tank. If the pressure in port (5) falls, spring (7) moves the spool back to the right allowing extra oil to pass into port (5) to maintain the controlled pressure.

Solenoid Valve

Solenoid Valve
1. Spring 2. Port 3. Port 4. Port 5. Solenoid 6. Core 7. Plug 8. Pin 9. Spring 10. Spool

Controlled pressure from the pressure reducing valve enters the solenoid valve through port (3). When the valve solenoid is de-energised spring (1) holds spool (10) to the right. Oil passes the valve spool and flows out through port (2) to port A on the valve sub plate, which is blocked. Port (4) is connected to tank and the lock up clutch is disengaged.

When the valve solenoid is energised a magnetic field is created which moves core (6) and pin (8) to the left. The pin pushes the spool to the left and the spool connects port (3) to port (4). Controlled pressure then flows to the lock up clutch, which engages.

Lock Up Electrical Circuit

Engagement of the torque converter lock up clutch requires a 24 volt DC supply to the solenoid valve (1). This condition requires that a pressure switch is closed and that magnetic pick up (2) is sending a signal of the required frequency to the speed switch.

Operation of the pressure switch is determined by the transmission hydraulic pump outlet pressure. The normally open switch closes when the oil pressure reaches a certain value.

The magnetic sensor (2) is mounted on the torque converter opposite drilled plates (3) which are fixed to the transmission drive shaft. As the shaft rotates the sensor sends pulses to the speed switch. When the frequency of these pulses reaches a certain value the speed switch closes and energises the valve solenoid.

If the signal from the pressure switch is lost or if the frequency of pulses from the magnetic sensor falls below a certain value the speed switch opens and the valve solenoid is de-energised. The frequency at which the speed switch re-opens is lower than the frequency at which it closes

Torque Converter Outlet Relief Valve

Outlet Relief Valve
1. Valve Body 2. Inlet Passage 3. Outlet Passage 4. Spring 5. Shims 6. Spool 7. Poppet Valve

The outlet relief valve controls the maximum pressure in the torque converter.

Oil leaving the torque converter enters the valve body (1) through passage (2). The oil passes through a hole in the valve spool (6), unseats poppet valve (7) and acts against the end of the spool. As the pressure of the converter outlet oil increases the valve spool moves against the effect of spring (4). As the spool moves outlet passage (3) is connected to inlet passage (2) and converter outlet oil flows to the oil cooler.

Shims (5) are provided to adjust the relief setting.