953D, 963D and 973D Track-Type Loaders Brake Does Not Release Caterpillar


Brake Does Not Release
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953D, 963D and 973D Track-Type Loaders [KENR6327]
BRAKING SYSTEM
953D, 963D and 973D Track-Type Loaders Brake Does Not Release
1.1. Probable Causes
2.1. Recommended Actions
3.2. Contamination Of The Hydraulic System Oil
4.2. Insufficient Pressure Oil To The Brakes
5.2. Charge System Pressure Is Not Correct
6.2. Failed Brake Components
7.2. The Brake Solenoid Valve Is Not Functioning Properly

Probable Causes

  • Contamination of the hydraulic system oil

  • Insufficient pressure oil to the brakes

  • Charge system pressure is not correct.

  • Failed brake components

  • The brake solenoid valve is not functioning properly.

Recommended Actions

------ WARNING! ------

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.



NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "AVSpare Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on AVSpare products.

Dispose of all fluids according to local regulations and mandates.


Follow this procedure if the machine does not move or if the machine moves slowly.

Initially, ensure that the symptom is active. If the symptom is intermittent then a probable cause is oil contamination.

Next, a check of the brake pressure guides the diagnosis of the problem to the brake system or to the hydrostatic transmission.

If the brake pressure is correct then the hydraulic system is eliminated as the probable cause of the problem. The electrical system is also eliminated as the probable cause of the problem. Thus, sufficient pressure is sent to the brake in order to release the brake. Therefore, an issue in the hydrostatic transmission is the probable cause.

If the brake pressure is not correct then the hydraulic system or the electrical system is the probable cause of the problem. Next, a check of the system pressure determines if the system pressure is high enough. The system pressure allows the brake solenoid to supply sufficient pressure to the brakes.

If the charge system pressure is correct then check the brake solenoid valve. If the brake release pressure is correct then a mechanical problem may exist. If the brake release pressure is low then there could be a problem in the charge system. This check guides the diagnosis of the problem to the brake control valve or to the brakes.

Contamination Of The Hydraulic System Oil

If the symptom is not active or if the symptom is intermittent, oil contamination may be the problem.

Remove any contaminants from the oil by filtering the oil that is used in the machine.

Change the hydrostatic transmission and hydraulic system oil. Change the oil filter element and clean the screens. Refer to Operation and Maintenance Manual, "Hydraulic System Oil - Change" for the 953D and the 963D machines. Refer to Operation and Maintenance Manual, "Hydrostate Transmission and Hydraulic System Oil - Change" for the 973D machines.

Insufficient Pressure Oil To The Brakes

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

Charge System Pressure Is Not Correct

Check the charge system pressure.

Reference: Refer to Testing and Adjusting, "Charge Relief Valve - Adjust" for your machine.

Expected Results

  • The charge system pressure is correct.

Results

  • OKAY: The charge system pressure is correct. Inspect the brake control valve. Proceed to "The Brake Solenoid Valve Is Not Functioning Properly".

  • NOT OKAY: The charge system pressure is not correct. The cause of the problem may be the adjustment of the charge relief valve. The pressure is controlled by the charge relief valve in the right side of the hystat pump. Control the system pressure by adjusting the charge relief valve. Refer to Testing and Adjusting, "Relief Valve - Test and Adjust" for your machine.

Failed Brake Components

Disassemble the brakes and check the following components of the brakes for failure:

  • seals

  • splines

  • friction discs

  • springs

  • brake plates

Replace any damaged components, if necessary.

Calibrate the hystat operator controls.

Reference: Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.

The Brake Solenoid Valve Is Not Functioning Properly

  1. Replace the brake solenoid valve.

  2. Calibrate the hystat operator controls.

    Reference: Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.

  3. Check the brake pressure.

    Reference: Refer to Testing and Adjusting, "Brake Pedal - Test" for your machine.

    Expected Results

    • The original problem is resolved.

    Results

    • OKAY: Stop.

    • NOT OKAY: The cause of the problem is uncertain. Please call technical support with the information that has been gathered.

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