D5R2 and D6R2 Track-Type Tractors Hydraulic System Oil Level Is Low Caterpillar

Personal injury or death can result from escaping fluid under pressure.
Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause 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

Hydraulic oil level in the tank is decreasing.
Leaks at fittings and other types of hydraulic line connections
The steering motor shaft seal is leaking excessively.
The seal on the steering pump shaft is leaking excessively.
The implement pump shaft seal has excessive leakage.
Hydraulic oil is leaking or seeping at a tube connection, a hose connection, or at the bypass valve

Recommended Actions

Note: Care must be taken in order to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the machine. You must be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component that contains fluid. Dispose of all fluids according to local regulations.

Hydraulic Oil Level In The Tank Is Decreasing

Inspect the following items of the hydraulic tank for oil leakage:

All of the weld joints
All of the bolted covers and components
All fittings
All hose flange connections

Oil may leak from the system from any one or all of the following conditions: Correct any of the problems that are found. Fill the hydraulic tank with the correct oil. Monitor the tank to ensure that the leaks have been stopped.

Welds are damaged
Covers and components have seals or gaskets installed improperly
Bolts and fittings are improperly torqued

Leaks At Fittings And Other Types Of Hydraulic Line Connections

Check for leaks at all fittings and connections of hydraulic oil hoses/lines/tubes in the system in question. Correct any problems that are found then retest the system.

Leaks at fittings and other types of hydraulic line connections may cause loss of oil flow and prevent components from attaining work pressures. Pressure loss generates complaints of weak force such as the blade tilt or the lift force and implements drifting while in the HOLD condition. Flow loss generates complaints of the component speed such as the fan speed or the cylinder speed.

Leaks at fittings and connections on the pressure side of pumps are a direct source of oil loss in the system. Oil loss may lead to component failure if the low oil levels are not monitored and pumps and motors are starved of oil.

Leaks at fittings and connections on the suction side of pumps are a direct source of oil aeration. Oil aeration may also cause damage (cavitation) to components and create excess or unusual noise as well.

The Steering Motor Shaft Seal Is Leaking Excessively

Damage or excessive wear of the seal around the steering motor output shaft may allow hydraulic oil (case drain) to leak past the shaft seal. The steering motor is installed in a bore at the top front of the main case. Hydraulic oil from the hydraulic system that leaks past the seal around the steering motor output shaft will drain directly into the main case. The main case is the oil reservoir for power train oil. This condition will cause the power train oil level to increase and at the same time, cause the hydraulic oil level to decrease.

To determine if the shaft seal is leaking, perform the following steps:

Remove the steering motor and wiggle the shaft to see if there is any movement.
If the shaft is loose, the worn or failed bearings have allowed the shaft to cause wear to the shaft seal.
1. Disassemble the steering motor and inspect for damage.
  ReferenceFor D5R2 models, refer to the latest revision of Disassembly and Assembly, UENR4118.
  ReferenceFor D6R2 models, refer to the latest revision of Disassembly and Assembly, UENR4108.

If the shaft does not wiggle, disconnect and remove the steering motor from the machine and bench test the motor.

Operate the motor at 425 psi in both directions.
Observe the shaft seal during bench test operation and look for signs of leakage.

If leakage is observed, replace the shaft seal.
Carefully examine the shaft for damage where the seal and shaft contact each other.

After repair and assembly, test the motor again and look for leakage at the shaft before reinstalling the motor.

The Implement Pump Shaft Seal Has Excessive Leakage

The pump drive components inside the flywheel housing are lubricated with power train oil.

Damage to the seal around the implement pump input shaft may allow hydraulic oil (at case drain pressure) to leak past the seal. Hydraulic oil that leaks past this seal will drain directly into the flywheel housing. The oil in the flywheel housing will drain into the torque divider housing. The power train oil scavenge pump transfers the oil back to the main sump for the power train oil.

This condition will cause the power train oil level to increase and at the same time, cause the hydraulic oil level to decrease.

Remove the implement hydraulic pump from the flywheel housing and inspect the input shaft seal for signs of damage and/or leakage. Repair or replace any damaged component or parts and reinstall the pump. Monitor for the symptom.

Oil Leaking Or Seeping At Tube Connections, Hose Connections, And At The Bypass Valve

Ensure that the machine is running and the oil is warmed to operating temperature to allow the bypass valve to close.

Perform the following inspection before cleaning the core:

Examine all surfaces, tubes, and connections on the hydraulic oil cooler for signs of leaks. If oil is leaking, dirt and dust will adhere to the oily surfaces more than dry surfaces. Tighten any loose connections or fittings that may be leaking and recheck for leaks.

Examine any suspected areas found during the initial inspection. Look for oil leaking or seeping at tube connections, hose connections, and at the bypass valve. Tighten any loose connections or fittings that might be leaking and recheck for leaks. The hydraulic oil cooler should be replaced if there are leaks on surfaces in addition to the fittings.

Thoroughly clean the cooler.