844K Wheel Dozer Caterpillar

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Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the power train.

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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.

Probable Causes Of Problems In The Torque Converter

The toque converter is a device that changes the ratio of torque to speed between the input and output shafts of the machine. The torque converter is a type of hydrodynamic fluid coupling that transfers rotating power from the engine to a rotating driven load.

Troubleshooting Problem List

• Torque converter pressure is high.

• Torque converter pressure is low.

• The torque converter overheats.

• The torque converter does not respond correctly for the left service brake pedal.

• The lockup clutch does not engage.

• The lockup clutch engages intermittently.

• The impeller clutch does not engage.

Troubleshooting

Note: Refer to the Hydraulic Schematic , UENR4895 for the 844K Wheel Dozer (HRC & LRC) to identify components that are referenced in the sections that follow.

Use the built-in electrical diagnostics that are performed with the electronic control module (ECM) to determine the service codes for the Transmission ECM and Implement ECM modules.

Note: This machine is equipped with a Transmission ECM and an Implement ECM. The control modules have built-in diagnostics that detect faults in the electronic system.

Torque Converter Pressure Is High

Probable causes:

• There is a restriction inside the torque converter.

• There is a restriction in an oil passage or in the oil cooler.

• The torque converter inlet ratio valve is stuck in the closed position.

• Power train oil is too cold.

Torque Converter Pressure Is Low

Probable causes:

• Torque converter inlet ratio valve is stuck in the open position.

Pump Flow Or Oil Pressure Is Low

This low pressure may be caused by any of the following conditions:

• The oil level is low.

• There is a restriction in the oil flow circuit or a dirty oil strainer.

• Air leaks on the inlet side of the pump.

• Oil pump failure.

• Leakage inside the transmission (worn seals around the clutch piston)

• Modulating relief valve is stuck open.

Oil Flow Through The Torque Converter Is Too Low

This low oil flow may be caused by any of the following conditions:

• Pump flow or oil pressure is low. Refer to the Problem: Torque converter pressure is low.

• Internal seal leakage inside the torque converter is too high.

• The transmission oil temperature gauge is faulty.

• The stator clutch has failed.

Torque Converter Overheats

Probable causes:

• 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 oil level in the transfer gear case is incorrectly high or low.

• The coolant level in the engine radiator is low.

• The oil cooler or oil lines are restricted.

Lockup Clutch Does Not Engage

Probable causes:

• The lockup clutch solenoid or the modulating valve for the lockup clutch is faulty.

• The torque converter output speed sensor is malfunctioning.

• There is a problem in the electrical circuit.

• There is excessive leakage in the lockup clutch.

• The magnetic screens are plugged. The oil flow to the lockup clutch is reduced.

• The lockup clutch is damaged.

• The power train oil pump is damaged.

Lockup Clutch Engages Intermittently

Probable cause:

• Erratic signals from the engine or the torque converter speed sensor cause the lockup clutch in the enabled torque converter to cycle on and off.