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.

Troubleshooting

Visual Checks

Clues about the nature of a transmission problem or failure can often be found during a visual inspection of the filter and magnetic screen.

Shiny steel particles in the filter indicate pump wear or failure. However the absence of such particles is no guarantee that the pumps are performing correctly. A pump problem may still exist.

Aluminium particles in the filter or magnetic screen indicate a torque converter failure.

Rubber particles in the filter or magnetic screen indicate a seal or hose failure.

Iron or steel chips in the magnetic screen indicate broken parts in the transmission, torque converter or transfer drive.

If rubber, aluminium, iron or steel particles are found it is essential that the system and all its components are washed clean to avoid a second failure. Do not risk using damaged parts. Always install new parts.

Checks During Operation

Before starting to do any operational checks or pressure testing, be sure that:

The filter is clean.

The magnetic screen is clean.

The transmission oil level is correct.

All pipes, hoses and connectors are leak free.

Many of the problems which follow could be due to one or more of the above conditions being wrong.

Torque Converter

PROBLEM: Lock-up clutch will not engage.

POSSIBLE CAUSES:

1. Transmission pump faulty or worn. Other problems will be noticed. For example, transmission clutch slip, slow shifts, poor torque converter performance.

2. Magnetic sensor faulty or incorrectly set.

3. Lock up pressure switch faulty.

4. Solenoid valve spool stuck or solenoid burned out.

5. Speed switch faulty or incorrectly set.

6. Clutch plates damaged or worn.

7. Leakage across clutch piston.

8. Pressure reducing valve set too low.

PROBLEM: Overheating.

POSSIBLE CAUSES:

1. Oil cooler clogged or not receiving sufficient coolant flow (engine coolant level low).

2. Lock-up clutch slipping due to low pressure or worn plates.

3. Wrong gears being used-torque converter operating near stall for long peroids.

4. Worn or damaged converter allowing excessive internal leakage.

5. Torque converter inlet pressure valve (part of transmission control valve group) not operating correctly. Check converter inlet pressure.

PROBLEM: High converter inlet pressure.

POSSIBLE CAUSES:

1. Torque converter inlet pressure valve not opening

PROBLEM: Low converter inlet pressure.

POSSIBLE CAUSES:

1. Torque converter inlet pressure valve opening too early.

PROBLEM: Torque Converter outlet pressure low.

POSSIBLE CAUSES:

1. Low converter inlet pressure.

2. Converter worn or damaged.

PROBLEM: Engine speed too high at torque converter stall.

POSSIBLE CAUSES:

1. Transmission clutch slippage.

2. Torque converter damaged or worn resulting in excessive leakage.

PROBLEM: Engine speed too low at torque converter stall.

POSSIBLE CAUSES:

1. Freewheel assembly damaged.

2. Engine output torque low - engine may need tuning.

Transmission

PROBLEM: Transmission shifts slowly.

POSSIBLE CAUSES:

1. Air leaks on inlet side of oil pump.

2. Failure in the transmission pressure control valve.

PROBLEM: Transmission clutches engage very suddenly (rough shifts).

POSSIBLE CAUSES:

1. Initial pressure setting of modulation relief valve not correct.

2. Load piston stuck.

3. Operation of pressure differential and safety valve not correct.

4. Springs in the pressure control valve weak or damaged.

PROBLEM: Transmission does not operate in any speed or clutches slip in all speeds.

POSSIBLE CAUSES:

1. Failure of oil pump.

2. Air leaks on inlet side of pump.

3. Modulation relief valve not operating correctly.

4. Too much leakage inside the transmission.

5. Failure in the transmission pressure control valve.

6. Mechanical failure in the transmission.

7. Mechanical failure in transfer drive.

8. Mechanical failure in differentials.

9. Torque converter failure.

PROBLEM: Transmission engages but the machine does not move and the engine stops.

POSSIBLE CAUSES:

1. Mechanical failure in the output transfer drive.

2. Mechanical failure in differential.

3. Mechanical failure in a final drive.

4. Mechanical failure in transmission.

PROBLEM: Low clutch pressures.

POSSIBLE CAUSES:

1. Clutch seal rings damaged.

2. Operation of modulation relief valve not correct.

PROBLEM: High pressure at pressure taps for clutches in all speeds and directions.

POSSIBLE CAUSE:

1. Operation of modulation relief valve not correct.

PROBLEM: High pressure at direction clutch pressure tap in both directions.

POSSIBLE CAUSE:

1. Operation of pressure differential/safety valve not correct.

PROBLEM: Low pressure at pressure taps for speed and direction clutches in all speeds and directions.

POSSIBLE CAUSES:

1. Operation of modulation relief valve not correct.

2. Operation of load piston not correct.

PROBLEM: Low pressure at direction clutch pressure tap in REVERSE speeds.

POSSIBLE CAUSE:

1. Too much leakage in the No. 1 clutch.

PROBLEM: Low pressure at direction clutch pressure tap in FORWARD speeds.

POSSIBLE CAUSE:

1. Too much leakage in the speed clutch for that speed.

PROBLEM: Low lubrication pressure.

POSSIBLE CAUSES:

1. Pump faulty or worn.

2. Relief valve stuck open.

PROBLEM: Pump noise.

POSSIBLE CAUSES:

1. Loud sounds at short intervals that give an indication that particles are going through the pump is caused by pump cavitation.

2. A constant loud noise is an indication of pump failure.

3. Air at the inlet side of the pump (aeration).

Pump Pressure

The pump pressure can be checked by installing a pressure gauge in the test port provided.

Pump Pressure Test Port - Early Trucks

Pump Pressure Test Port - Later Trucks

Pump Pressure Test Port - Current Trucks

The pressure should be the same as the speed clutch pressure. If the speed clutch pressure is known to be low, check the pump pressure. If the speed clutch pressure is correct there is no point in checking the pump pressure.

The pump pressure cannot be adjusted independently of the speed clutch pressure.

Speed and Directional Clutch Pressures

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The machine can move during testing if proper precautions are not taken. This can result in personal injury or death. To prevent this from happening, do the following: 1. Park the machine on a hard level surface and block the wheels. 2. Remove the axle shafts. It is possible to prevent the machine from moving during testing by removing only one front axle shaft and disengaging the Inter-axle differential lock. THIS IS NOT RECOMMENDED because: a. The position of the differential lock switch cannot be relied upon as a positive indication that the lock is disengaged. THERE COULD BE A FAULT. b. Even if the mechanism is disengaged it is possible for it to be accidentally reengaged during testing either by another person or due to a fault. c. The front axle may contain a NoSpin differential.

A quick check of speed clutch pressure can be made using the pump pressure test point. Speed clutch pressure is the same as pump pressure. To make a more comprehensive check proceed as follows.

1. Remove the transmission hydraulic control valve group cover and install pressure gauges in test ports (P1) and (P2). If available, use 5P6586 cover. If the cover is not available make a suitable cover from a clean piece of board or polythene with holes to allow the gauges to be installed. A cover is necessary to avoid oil splashes.

2. Remove load piston plug LP.

3. Start the engine and operate at low idle.

4. Place the speed selector lever in FIRST speed and the directional selector lever in NEUTRAL. The pressure gauge in port P1 (speed clutch) should register the initial pressure given in the transmission pressures chart.

5. Stop the engine and replace plug LP.

6. Restart the engine, move the directional selector to FORWARD and operate at high idle. The pressure gauges should register the values given in the transmission pressures chart.

7. Allow the engine speed to fall to low idle and compare the pressure readings with the values given in the transmission pressures chart.

8. Check the operation of the pressure differential/safety valve (see below) before removing the test equipment.

Pressure Differential/Safety Valve

The following procedure follows from the procedure described under "Speed and Directional Clutch Pressures" and assumes that the axle shafts have been removed and the necessary test equipment is installed.

1. Stop the engine.

2. With the directional selector lever in either FORWARD or REVERSE re-start the engine and operate at high idle. The speed clutch pressure (P1) should build up to the correct value but the directional clutch pressure (P2) must remain zero.

3. Move the selector lever to NEUTRAL. The directional clutch pressure gauge (P2) should register the correct value.

4. Stop the engine.

Torque Converter Inlet Pressure

Check the torque converter inlet pressure when the transmission oil is cold, if possible.

1. Install a pressure gauge in test port P3.

2. Start the engine and operate at high idle. The pressure gauge should register the value given in the transmission pressures chart.

Torque Converter Outlet Pressure

1. Install a pressure gauge in the test port on the outlet relief valve.

2. With the service brakes applied, run the engine at high idle in fourth speed and note the pressure reading.

3. Compare the converter outlet pressure reading with the value given in the transmission pressures chart.

4. Shut down the engine, remove the pressure gauge and replace the test port plug.

Lubrication Pressure

1. Install a pressure gauge in the lubrication test port.

2. Start the engine and operate at high idle. The lubrication pressure will be displayed on the pressure gauge. See the transmission pressures chart.

Speed Clutch Pressure Adjustment

The initial pressure setting of the speed clutches can be adjusted by adding or removing shims(2) from load piston(1). The addition of shims will increase the pressure setting.

Torque Converter Outlet Pressure Adjustment

The torque converter outlet pressure can be adjusted by adding or removing shims(1) from the valve spool(2). The addition of shims increases the relief valve setting.

Outlet Relief Valve
1. Shims 2. Spool

Torque Converter Stall Speed

The torque converter stall speed should be checked with the transmission oil at normal working temperature.

1. Start the engine and operate at low idle.

2a. Early Machines:

Move the park brake lever to the SEC position. This applies the parking and service brakes simultaneously.

2b. Later Machines:

Move the parking brake lever to the PARK position. This applies all wheel brakes.

3. Engage fourth speed forward.

4. Increase the engine speed while observing the tachometer. When the engine speed stops rising torque converter stall speed has been reached.

5. Select neutral, move the parking brake lever to PARK (early machines) and shut down the engine.

The correct torque converter stall speed is 1810 - 1930 r.p.m.

The stall speed obtained using the machine tachometer is unlikely to be very accurate. If an accurate reading is required it will be necessary to check the tachometer.

1. Mount a Caterpillar 6V3121 multitach group to measure the transmission drive shaft speed. Caterpillar Special Instruction form number SEHS7807 gives instructions for using the multitach group.

2. Engage neutral, start the engine and operate at the measured torque converter stall speed. If the stall speed was measured as 1850 r.p.m. using the machine tachometer then run the engine at 1850 r.p.m. on the machine tachometer.

3. Measure the transmission drive shaft speed with the multitach group. The torque converter should be locked up so that the drive shaft speed should be the same as engine speed. The multitach reading should therefore be an accurate measure of torque converter stall speed.

Lock Up Clutch Test

1. Install a pressure gauge in the lock up test port.

Test Port - Early Machines

Test Port - Later Machines

2. Check that the park brake is applied and that the transmission selector is in neutral.

3. Start the engine and increase the engine speed while observing the pressure gauge. If the engine is started from cold allow it to idle for a few moments before increasing speed.

4. The gauge should register zero pressure while the clutch is disengaged. The dash indicator should be illuminated at the same time.

5. Increase the engine speed until the transmission input speed is high enough to cause lock-up clutch engagement. The pressure gauge should then register the value given in the transmission pressures chart.

6. If the gauge does not register pressure check the following:

a) Magnetic sensor.

b) Speed switch.

c) Pressure switch

d) Solenoid valve.

7. If the gauge reading does not remain constant within 70kPa(10p.s.i.) the pressure reducing valve may be faulty. Disassemble and clean or replace the valve.

8. If the pressure does not register check the lock up clutch control circuit for correct operation.

9. If the pressure gauge shows the correct reading but the clutch still fails to engage properly, mechanical damage or wear is indicated.

10. If the engine speed is too high or low when the lock-up clutch engages the speed switch may require adjustment. The clutch is engaged when the gauge registers pressure. The dash indicator should go out at the same time.

This is a no load test during which the engine speed is ASSUMED to equal the transmission input speed. There will be a some torque converter slip even during a no load test. Since the magnetic pick up is sensing torque converter output speed (which will be slightly lower than engine speed) the clutch engage speed measured on the machine tachometer will be approximate. Do not adjust the speed switch until the engage and disengage speeds have been accurately checked by measuring transmission drive shaft speed with a suitable tachometer such as the 6V3121 multitach group.

11. If the checks described above are satisfactory, operate the engine at high idle and gradually reduce the engine speed until the gauge reading falls to zero. This is the engine speed at which the lock up clutch disengages.

NOTE: The above procedure provides an approximate check for lock up engage/disengage speeds using the machine tachometer. If an accurate measure is required use a 6V3121 multitach group to measure transmission drive shaft speed. Special Instruction SEHS7807 gives instructions for using the multitach group. When checking the engage/disengage speeds by measuring transmission drive shaft speed, observe the tachometer very carefully. As the lock up clutch engages there will be a small, instantaneous increase in shaft speed. The correct engage speed is the speed measured immediately before this increase. Similarly, as the lock up clutch disengages there will be a small, instantaneous decrease in shaft speed. The correct disengage speed is the speed measured immediately before this decrease.

Lock Up Pressure Adjustment

The lock up pressure can be adjusted if necessary using the adjusting screw on the pressure reducing valve.

Pressure Reducing Valve
1. Adjusting Screw 2. Jam Nut

1. Check the lock up clutch pressure.

2. If the reading is incorrect loosen the jam nut (2) and turn adjusting screw (1) until the correct reading is obtained. Turn the screw in to increase the pressure.

3. When the reading is correct lock the adjusting screw in place with jam nut (2), stop the engine and remove the test gauge.

Speed Switch Adjustment

Do not adjust the speed switch unless the engage/disengage speeds have been checked by measuring transmission drive shaft speed.

If the lock up engage or disengage speeds are incorrect they can be adjusted by turning screws VR2 and VR3.

Machines with 5U6140 Speed Switch

5U6140 Speed Switch

Turn VR2 counter-clockwise to raise the lock up engage speed and turn VR3 counter-clockwise to raise the disengage speed. Fix the screws with varnish or paint to prevent vibration loosening. Do not turn screw VR1.

Machines with 6U9025 Speed Switch

6U9025 Speed Switch

Turn VR3 counter-clockwise to raise the lock up engage speed and turn VR2 counter-clockwise to raise the disengage speed. Fix the screws with varnish or paint to prevent vibration loosening. Do not turn screw VR1.

Magnetic Pick Up Adjustment

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The magnetic pick up is located next to a drive shaft which rotates when the engine is running. This can cause personal injury or death. Make sure the engine is stopped, post a "DO NOT OPERATE" warning tag on the start switch and keep all unauthorised personnel off the machine.

The magnetic pick up is located on the torque converter output yoke. The pick up should be set as follows:

1. Stop the engine, open the battery isolator switch and remove the key.

Magnetic Pick Up
1. Jam Nut 2. Plate

2. Loosen the jam nut(1) and turn the pick up in until it touches the plate(2).

3. Turn the pick up back by half a turn (no less) and tighten the jam nut.

Lock Up Circuit Electrical Testing

If an electrical fault is suspected in the lock up circuit, carry out the following checks:

1. Remove the wires from the pressure switch and connect a resistance meter across the switch terminals. With the engine stopped the meter should indicate an open circuit (very high resistance). When the engine is started the meter should indicate a closed circuit (very low resistance). If the switch does not behave as expected it is either faulty or the transmission pressure is not high enough to close it. If the switch remains open when the engine is running (open circuit) check the pump pressure. If the pump pressure is normal the switch is faulty.

Pressure Switch - Early Machines

Pressure Switch - Later Machines

Pressure Switch - Current Machines

2. Check the solenoid valve coil for electrical continuity by removing the plug and connecting a resistance meter across the terminals. The meter should indicate approximately 20 ohms. If the meter indicates very high resistance (open circuit) the solenoid has burned out.

5U6140 Speed Switch Installed.

3. Remove the wires from speed switch terminals V+ and V-. Connect a DC voltmeter across these two wires. Switch on the electrical circuits (close the battery isolator switch). The meter should indicate battery voltage (24 volts). If it does not the supply is faulty.

Switch off the circuits by opening the battery isolator switch and connect the wires to the speed switch terminals.

4. Connect a high impedence AC voltmeter across speed switch terminals S+ and S-. Start the engine and observe the meter carefully. If the magnetic sensor is operating correctly a deflection of the meter will be observed. It may be necessary to increase the engine speed and/or set the meter on a more sensitive range to obtain any deflection. If no deflection is observed then the sensor is either faulty or out of adjustment.

Stop the engine, remove the wires from terminals S+ and S- and connect a resistance meter across the two wires. The meter should indicate a resistance of 360-440 ohms. If the resistance is outside this specification the sensor is probably faulty.

5. Connect a DC voltmeter across speed switch terminals NO and V-. Start the engine and increase speed to above the value normally required to engage lock up (1450 r.p.m.). If the meter fails to register 24 volts (battery voltage) the speed switch is probably faulty.

6. Connect a resistance meter across relay terminals 85 and 86. If the meter registers very high resistance (open circuit) the relay coil has burned out. The relay coil resistance should be about 250 ohms.

If the coil is intact, apply a DC voltmeter across relay terminals 30 and 87 and increase the engine speed to above the value required to cause lock up clutch engagement. The meter should register battery voltage if the relay is closing correctly.

6U9025 Speed Switch Installed

3. Remove the dash retaining screws and lift the dash to gain access to the plug and socket connecting the speed switch wires to the dash wiring. Disconnect the plug and socket.

4. Connect a DC voltmeter between the brown wire in the plug and ground (earth). Switch on the electrical circuits (close the battery isolator switch). The meter should indicate battery voltage (24 volts). If it does not the supply is faulty.

Switch off the circuits by opening the battery isolator switch.

5. Connect a high impedence AC voltmeter between the red/blue and red/green wires in the socket. Start the engine and observe the meter carefully. If the magnetic sensor is operating correctly a deflection of the meter will be observed. It may be necessary to increase the engine speed and/or set the meter on a more sensitive range to obtain any deflection. If no deflection is observed then the sensor is either faulty or out of adjustment. Stop the engine and connect a resistance meter across the two wires. The meter should indicate a resistance of 360-440 ohms. If the resistance is outside this specification the sensor is probably faulty.

6. Connect the plug and socket and connect a DC voltmeter between the red/orange wire in the socket and ground(earth). Start the engine and increase speed to above the value normally required to engage lock up (1450 r.p.m.). If the meter fails to register 24 volts (battery voltage) the speed switch is probably faulty.