910K, 910M, 914K, 914M, 918M, and 920K Wheel Loaders Machine Electronic Control System Caterpillar

Transmission Troubleshooting Problem List

Note: Many of the following problems can create diagnostic codes or event codes in Cat ET. These codes can help find the root cause of the problem. Cat ET should be used to retrieve the logged codes and active codes.

High Transmission Oil Temperature

• Check the transmission (gearbox) oil level. The oil level may be overfull or low.

• The transmission oil temperature sensor is faulty.

Hydrostatic Motor Overspeed

1. Motor 2 clutch will not disengage due to an internal clutch failure.

2. Clutch will not disengage due to the clutch valve being stuck in the ON position.

Likely source of problem 2.

• Oil too cold or too viscous

• Oil contaminants above acceptable level

Transmission Stuck In Range 1 Or Range 2

1. Clutch will not disengage due to an internal clutch failure

2. Clutch will not disengage due to the clutch valve being stuck on

Likely source of problem 2.

• Oil too cold or too viscous

• Oil contaminants above acceptable level

• Shifting is not allowed due to a speed sensor fault.

The Machine Has Low Rimpull

• The machine is in the low rimpull setting on the keypad control.

• The clutch is slipping due to a clutch failure.

• There is low or no clutch pressure due to a problem with the clutch valve, transmission lube pump, or a leak in the clutch circuit.

• The oil level is too low in the transmission.

The Transmission Does Not Operate Or Move In Any Range

• There is an internal transmission gear or shaft failure.

• The parking brake is stuck on and will not disengage.

• The service brakes are locked up.

• There is a mechanical failure in the axle differential or final drive.

• There is a driveshaft failure.

• There is an electrical fault, check Cat ET for active codes.

• The direction selector or range selector keypad is faulty.

• There is low transmission lube pump pressure or low hydrostatic charge pressure.

• The hystat interlock solenoid valve is stuck closed.

• There is an internal hystat pump or motor failure.

• Pump solenoid is faulty

• Low hydraulic oil level

Unusual Transmission (gearbox) Noise

• Internal transmission error caused by wear/damage, improper end play setting, or improper shaft balancing.

• The transmission lube pump has failed.

• Motor 2 clutch engagement is harsh.

Unusual Hystat (pump and motor) Noise

• Hystat charge pressure is low

• Hystat pump/motor internal bearing worn or failed

• Hystat hose routing issue

• Hydraulic oil has air bubbles

• Low hydraulic oil level

Motor 2 Clutch Engagement/Disengagement Is Harsh

• The clutch fill calibration is incorrect.

• The pump or motor solenoid calibration is incorrect.

• Motor 2 clutch has failed

• Incorrect speed signal from speed sensors.

The Transmission Operates, But The Speed Is Slower Than Normal

• Incorrect speed reading from transmission speed sensors.

• Motor 1 solenoid valve is faulty.

• Motor 2 solenoid valve is faulty.

• Left pedal calibration incorrect

• Incorrect pump/motor calibration

• Hystat charge pressure is low

• Pump/motor internal damage

• Motor flushing valve open in direction of travel

The Transmission Operates In Forward Only

• The pump reverse solenoid is stuck closed.

• The pump reverse COR/make-up valve stuck open.

• There is an internal hydrostatic pump failure.

• The motor flushing valve is open in the reverse direction of travel.

The Transmission Operates In Reverse Only

• The pump forward solenoid is stuck closed.

• The pump forward COR/make-up valve stuck open.

• There is an internal hydrostatic pump failure.

• The motor flushing valve is open in the forward direction of travel.

The Transmission Operates, But The Machine Acceleration Is Slower Than Normal

• Hystat charge pressure is low

• Machine or hystat power is low

• Motor 2 clutch is slipping or not engaged

• The motor flushing valve is open in direction of travel.

Deceleration Of Machine Using Left Pedal Is Inadequate Or Jerky

• Check the Left Pedal calibration

• Check the Hystat pump/motor calibration

• Pedal sensor is faulty

Hystat Power Is Too Low

• Ensure that the engine is operating correctly.

• The hydraulic oil is low. Check the hydraulic oil level.

• Hydraulic oil temperature is too hot. Check the oil temperature sensor.

• Check to ensure that clutch engages and disengages correctly.

• There are air bubbles in the oil.

• Check to make sure that the cross over relief is not stuck open at lower system pressures.

• Check the electronic pressure override calibration.

• Check the cross over relief valve (COR) makeup valves. Makeup valves may be stuck open.

Machine Speed Surges

• Check to make sure the flushing valve in not stuck in the direction of travel.

• Hystat pump/motor calibration may be needed.

• A pump or motor solenoid may be faulty.

Hydraulic Oil Temperature Is Too High

• Check the hydraulic oil cooler for blockage.

• Check the transmission case and cooler lines for blockage.

• Check to ensure that the hystat pump bypass check valve is not stuck open at an oil temperature higher than 60° C (140° F)

• Check to ensure that the bypass check valve at the hystat motor block is not stuck open.

• Check the cross over relief (COR)/make up valve pressure on either direction for any stuck open relief valves.

• Check the electronic pressure override calibration.