D7 Track-Type Tractor Electrohydraulic Systems Brake Does Not Engage Caterpillar

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

Probable Cause

• Excessive system pressure

• Brake components have failed

• 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 brake control valve.

If the brake pressure is correct, then the 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 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.

Excessive 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 brake control valve to the brakes. Therefore, excessive pressure oil to the brakes is a probable cause of the symptom.

   Reference: Refer to Systems Operation/Testing and Adjusting, M0064234, "Brake Pressure - Test".

   Expected Results

   • The pressure is correct.

   Results

   • OKAY: Since the pressure at the 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 brake control valve to the brakes. Therefore, high-pressure oil from the brake control valve to the brakes is a probable cause of the symptom. Proceed to "Brake Control Valve".

Brake Components Have Failed

1. Check the brakes.

   The brake pressure 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.

   Reference: Refer to Systems Operation/Testing and Adjusting, M0064234, "Calibration" for the appropriate calibration procedure.

   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 "Brake Control Valve".

Brake Control Valve

1. Disassemble the brake control valve and inspect the valve for damage. Look for damaged o-ring seals.

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

3. Calibrate the brakes.

   Reference: Refer to Systems Operation/Testing and Adjusting, M0064234, "Calibration" for the appropriate calibration procedure.

   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. Disassemble the Proportional Solenoid valve and inspect the valve for damage.

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

3. Calibrate the brakes.

   Reference: Refer to Systems Operation/Testing and Adjusting, M0064234, "Calibration" for the appropriate calibration procedure.

4. 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: The cause of the symptom is uncertain. Call technical support with the information that has been gathered.