966M and 972M Wheel Loaders Caterpillar

Transmission

Usage:

972M A78

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Personal injury or death can result from sudden machine movement.
Sudden movement of the machine can cause injury to persons on or near the machine.

To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

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Personal injury can result from hydraulic oil pressure and hot oil.
Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system.

Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Escaping fluid under pressure, even a pinhole size leak, can penetrate body tissue, causing serious injury, and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

Always use a board or cardboard when checking for a leak.

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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products. Dispose of all fluids according to local regulations and mandates.

Probable Causes of Transmission Problems

The following is a list of possible causes that should be considered when specific conditions have been identified.

Transmission Operational Checks

Note: Operate the machine in each direction and in all speeds. Note the noises that are not normal and find the sources of the noises. If the machine is not operating correctly, refer to the "Clutch Engagement Is Sudden, Causing Jerky Shifting" below.

Troubleshooting Problem List

The transmission does not operate in any speed or the transmission slips in all speeds.
The transmission overheats.
Pump noise that is not heard normally.
Noise in the transmission that is not normal
The transmission operates in FORWARD only.
The transmission operates in REVERSE only.
The transmission does not operate in FIRST SPEED FORWARD or in FIRST SPEED REVERSE.
The transmission does not operate in SECOND SPEED FORWARD or in SECOND SPEED REVERSE.
The transmission does not operate in THIRD SPEED FORWARD or in THIRD SPEED REVERSE.
The transmission does not operate in FOURTH SPEED FORWARD or in FOURTH SPEED REVERSE.
Pressure is low at speed clutch pressure tap P1 and direction clutch pressure tap P2 when the machine is operated in all directions and speeds.
Pressure is low at direction clutch pressure tap P2 when the machine is operated in REVERSE speeds.
Pressure is low at direction clutch pressure tap P2 when the machine is operated in FORWARD speeds.
Pressure is high at speed clutch pressure tap P1 and direction clutch pressure tap P2 when the machine is operated in all directions and speeds.
The pressure differential between P1 and P2 is not correct.
Clutch engagement is sudden. (Sudden engagement causes jerky shifting.)
Clutch engagement is slow. (Slow engagement causes slow shifting in all gears.)
Clutch engagement is slow in all FORWARD gears, in all REVERSE gears, or in any one gear speed (FORWARD and REVERSE).
The machine does not move and engine speed lugs when the transmission is engaged.
The engine is running and the parking brake is engaged. However, the action alarm does not sound when the transmission is put into the FORWARD direction or into the REVERSE direction.
The backup alarm does not sound when the transmission is put in REVERSE.
Stall speed is low.
Stall speed is high when the machine is operated in both directions.
Stall speed is high when the machine is operated in one direction or in one speed.

Troubleshooting

Note: In the following section, refer to Hydraulic Schematic , KENR5563 and Electrical Schematic , KENR5564 when troubleshooting the machine.

Check for any service codes that may have been generated before troubleshooting a problem. Use the built-in electrical diagnostics that are performed with the electronic control module to determine the service codes for the electronic control module.

Note: This machine is equipped with a Machine electronic control. The Machine electronic control has built-in system diagnostics used to detect faults in the electronic system. For additional information on the operation and troubleshooting of the electronic control module (ECM), refer to the Service Manual module for Systems Operation, Testing and Adjusting, UENR0376, "966M/972M MACHINE SYSTEMS OPERATION/TESTING & ADJUSTING (COMBINED)".

The Transmission Does Not Operate In Any Speed Or The Transmission Slips In All Speeds

Probable causes include:

The fuse for the power train control is missing or broken.
There is a problem in the electrical circuit.
Oil pump is not primed.
Oil pump failure.
There is an electrical or mechanical problem with the main relief valve.
There is a hydraulic fluid leak.
The torque converter is not primed.
Torque converter failure.
Mechanical linkage between the torque converter and the transmission failure.
Multiple transmission clutch failure.
Parking brake failure.
Service brake or lower power train failure.

Oil Pressure Is Low

Probable causes include:

The oil level is low.
There is a dirty oil strainer or a restriction in the oil flow circuit.
Oil pump failure.
Air leaks on the inlet side of the pump.
There is leakage inside the transmission (worn seals around the clutch piston).
The modulating relief valve is stuck open.
There is a torque converter failure.
There is a mechanical failure in the transmission.
Clutch discs and clutch plates are excessively worn.

The Transmission Overheats

Probable causes include:

Coolant level in the radiator is low.
The machine is being used for the wrong application. There is too much torque converter slip, which is caused by too much load.
Incorrect transmission gear is being used for the load that is on the machine. Shift to a lower gear.
The temperature gauge is faulty.
The oil level is incorrectly high or low.
The oil cooler or oil lines are restricted.

The Clutch Slips Too Much

Probable causes include:

Low oil pressure. Refer to the Problem: The Transmission Does Not Operate In Any Speed Or The Transmission Slips In All Speeds.
A clutch is damaged.
Oil flow is low. Low flow may be caused by pump wear or by leakage in the transmission hydraulic system.
There is air in the oil. Air in the oil may be caused by air leaks on the intake side of the pump.
The magnetic screen for the pump inlet is plugged.
The torque converter inlet ratio valve is stuck open. A stuck valve causes low oil flow through the torque converter.

The Clutch Or Clutches Are Not Fully Released ("Clutch Drag")

Probable causes include:

There are warped plates or warped discs.
A return spring is broken or weak.

Pump Noise That Is Not Heard Normally

Probable causes include:

A loud noise at short intervals indicates that foreign material is in the transmission hydraulic system.
A constant loud noise indicates pump failure.
There is air at the inlet side of the pump.

Noise In The Transmission That Is Not Normal

Probable causes include:

Transmission components are worn or damaged.
Gears are damaged.
The teeth of the clutch plates and/or clutch discs are worn.
The clutch plates are slipping or noise from the clutch discs.
There are other transmission components that are worn or damaged.

The Transmission Operates In FORWARD Only

Probable causes include:

Number 1 REVERSE clutch solenoid is inoperative.
There is a problem in the electrical circuit.

The REVERSE Clutch Is Not Engaged Or The REVERSE Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

The Transmission Operates In REVERSE Only

Probable causes include:

Number 2 FORWARD clutch solenoid is inoperative.
There is a problem in the electrical circuit.

The FORWARD Clutch Is Not Engaged Or The FORWARD Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

The Transmission Does Not Operate In FIRST SPEED FORWARD Or In FIRST SPEED REVERSE

Probable causes include:

Number 6 speed clutch solenoid FIRST SPEED is inoperative.
There is a problem in the electrical circuit.

The FIRST SPEED Clutch Is Not Engaged Or The FIRST SPEED Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

The Transmission Does Not Operate In SECOND SPEED FORWARD Or In SECOND SPEED REVERSE

Probable causes include:

Number 5 speed clutch solenoid SECOND SPEED FORWARD is inoperative
There is a problem in the electrical circuit.

The SECOND SPEED Clutch Is Not Engaged Or The SECOND SPEED Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

The Transmission Does Not Operate In THIRD SPEED FORWARD Or In THIRD SPEED REVERSE

Probable causes include:

Number 4 speed clutch solenoid THIRD SPEED is inoperative.
There is a problem in the electrical circuit.

The THIRD SPEED Clutch Is Not Engaged Or The THIRD SPEED Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

The Transmission Does Not Operate In FOURTH SPEED FORWARD Or In FOURTH SPEED REVERSE

Probable causes include:

Number 3 speed clutch solenoid FOURTH SPEED is inoperative.
There is a problem in the electrical circuit.

The FOURTH SPEED Clutch Is Not Engaged Or The FOURTH SPEED Clutch Slips

Probable causes include:

Low oil pressure due to leaking piston seals.
The clutch discs and clutch plates have too much wear.
Clutch components are broken.

Pressure Is Low At Speed Clutch Pressure Tap P1 And Direction Clutch Pressure Tap P2 When The Machine Is Operated In All Directions And Speeds

Probable causes include:

The modulating relief valve is stuck.
Low oil pressure. Refer to the Problem: The transmission does not operate in any speed or the transmission slips in all speeds.
Springs of the load piston are weak or damaged. Springs or spacers are missing.

Pressure Is Low At Direction Clutch Pressure Tap P2 When The Machine Is Operated In REVERSE Speeds

Probable causes include:

There is too much leakage in the piston seals of the REVERSE clutch.

Pressure Is Low At Direction Clutch Pressure Tap P2 When The Machine Is Operated In FORWARD Speeds

Probable causes include:

There is too much leakage in the piston seals of the FORWARD clutch.

Pressure Is High At Speed Clutch Pressure Tap P1 And Direction Clutch Pressure Tap P2 When The Machine Is Operated In All Directions And Speeds.

Probable causes include:

The modulating relief valve is sticking.
The load piston is stuck.
The wrong load piston springs or too many spacers are being used.
The bore for the modulating relief valve is worn.

The Pressure Differential Between P1 and P2 Is Not Correct

Probable causes include:

Pressure differential valve is not operating correctly because of a spring that is weak or damaged.
The wrong spring may be installed.

Clutch Engagement Is Sudden, Causing Jerky Shifting

Probable causes include:

Pressure differential valve is not operating correctly because of a spring that is weak or damaged. Also, the wrong spring may be installed.
The load piston is stuck.
The wrong load piston springs are being used.
The load piston springs are damaged.

Clutch Engagement Is Slow.

Note: Slow clutch engagement causes slow shifting in all gears.

Probable causes include:

The screen orifice for the load piston is dirty or plugged.
Oil pressure is low. Refer to the Problem: The transmission does not operate in any speed or the transmission slips in all speeds.
The wrong load piston springs are being used or the load piston springs are damaged.
Modulating relief valve is stuck.

Clutch Engagement Is Slow In All FORWARD Gears, In All REVERSE Gears, or In Any One Gear Speed (FORWARD and REVERSE)

Probable causes include:

Clutch pressure is low because of leaking seals on the piston for the affected gear.

The Machine Does Not Move And The Engine Lugs When The Transmission Is Engaged

Probable causes include:

Service brakes are locked up.
The parking brake is not released. Also, the parking brake may be locked up.
There is a mechanical failure in a differential (front differential or rear differential).
There is a mechanical failure in a final drive.
Gears in the transmission do not turn because there is a mechanical failure in the transmission or too many clutches are engaged.