D5R2 and D6R2 Track-Type Tractors Brake Does Not Engage Caterpillar

Before you complete any procedure, read Troubleshooting, "Machine Preparation for Troubleshooting" in this module.

Probable Cause

• Insufficient system pressure

• Brake components have failed.

• Steering clutch and brake control valve

• Proportional solenoid valve

Recommended Actions

If the brakes are applied and the machine does not slow down or if the machine does not stop, follow this procedure.

The brakes are engaged with spring force. Hydraulic pressure is required to disengage the brakes. If hydraulic pressure is lost, the brakes fully engage due to the action of the spring force.

Initially, a check of the brake pressure guides the diagnosis of the symptom to the brakes or to the steering clutch and brake control valve.

If the brake pressure is correct, then the steering clutch and brake control valve is eliminated as the probable cause of the symptom. Thus, the brakes are the probable cause.

If the brake pressure is not correct, then the steering clutch and brake control valve is the probable cause of the symptom. If the brake pressure is corrected and the symptom still exists, then the brakes could be the second contributor of the symptom.

Insufficient Pressure Oil To The Brakes

1. Check the brake pressure.

   The brakes are engaged by spring force. The brakes are released by pressure oil which is sent from the steering clutch and brake control valve to the brakes. Therefore, insufficient pressure oil to the brakes is a probable cause of the symptom.

   ReferenceFor D5R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4119, "Steering Clutch and Brake Pressure - Test".

   ReferenceFor D6R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4109, "Steering Clutch and Brake Pressure - Test".

   Expected Results

   • The pressure is correct.

   Results

   • OKAY: Since the pressure at the steering clutch and brake control valve is correct, the brake control valve is eliminated as the cause of the symptom. The probable cause of the symptom is the brakes. Proceed to "Brake Components Have Failed".

   • NOT OKAY: The brakes are engaged by spring force. The brakes are released by pressure oil which is sent from the steering clutch and brake control valve to the brakes. Therefore, high-pressure oil from the steering clutch and brake control valve to the brakes is a probable cause of the symptom. Proceed to "Steering Clutch And Brake Control Valve".

Brake Components Have Failed

1. Check the brakes.

   The brake pressure is correct and the engagement of the transmission clutches is correct. The brakes are the probable cause of the symptom.

2. Disassemble the brakes and check the following components of the brakes for failure:
   • Brake housing

   • Reaction plate

   • Brake pistons

   • Belleville springs

   • Stationary ring gear

   • Seals

   • Splines

   • Friction discs

   • Brake plates

   • Shuttle valve

3. Replace any damaged components, if necessary.

4. Calibrate the brakes.
   

   ReferenceFor D5R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4119, "Calibration".

   ReferenceFor D6R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4109, "Calibration".

   Expected Results

   • The brake components are repaired or replaced. The original symptom is resolved.

   Results

   • OKAY: The brake components are repaired or replaced. The original symptom is resolved.

   • Stop.

   • NOT OKAY: The probable causes that were analyzed in this procedure did not identify the cause of the symptom. Use the information from the original symptom to troubleshoot. Proceed to "Steering Clutch And Brake Control Valve".

Steering Clutch And Brake Control Valve

1. Disassemble the steering clutch and brake control valve and inspect the valve for damage.

2. Repair the components and/or replace the components, if necessary.

3. Calibrate the brakes.
   

   ReferenceFor D5R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4119, "Calibration".

   ReferenceFor D6R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4109, "Calibration".

   Expected Results

   • The brake pressure is correct. The original symptom is resolved.

   Results

   • OKAY: The brake pressure is correct. The original symptom is resolved.

   • Stop.

   • NOT OKAY: If the pressure is correct but the original symptom still exists, proceed to "Proportional Solenoid Valve".

Proportional Solenoid Valve

1. Interchange the proportional solenoid valves.

2. Check the operation of the machine for the original symptom.

   Expected Results

   • The original symptom is resolved.

   Results

   • OKAY: Interchanging the proportional solenoid valves resolved the symptom.

3. Calibrate the brakes.
   

   ReferenceFor D5R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4119, "Calibration".

   ReferenceFor D6R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4109, "Calibration".

   • Stop.

• NOT OKAY: The brake pressure is not correct. The cause of the symptom may be something in the steering clutch and brake control valve. The proportional solenoid valves were eliminated as the cause. Proceed to Step 1.

1. Restore the solenoid valves to the original locations. Note the suspect valve.

   An obstruction in the steering clutch and brake control valve may have been dislodged. An obstruction can occur when the proportional solenoid valves are interchanged.

2. Check the original symptom to eliminate an obstruction as the cause of the symptom.

3. Operate the machine.

   Expected Results

   • The original symptom is resolved.

   Results

   • "OKAY": An obstruction in the steering clutch and brake control valve may have been displaced during the procedure. Change the oil. Change the oil filter elements. Clean the screens.

   • Stop.

   • "NOT OKAY": An obstruction is eliminated as a cause of the symptom. Proceed to Step 4.

4. Replace the proportional solenoid valve.

5. Check the operation of the machine for the original symptom.

   Expected Results

   • The original symptom is resolved.

   Results

   • OKAY: Calibrate the brakes.

   ReferenceFor D5R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4119, "Calibration".

   ReferenceFor D6R2 models refer to Specifications, Systems Operation/Testing and Adjusting, UENR4109, "Calibration".

• Stop.

• NOT OKAY: The cause of the symptom is uncertain. Call technical support with the information that has been gathered.