Pinpoint Test B: The Parking Brake Will Not Release
Parking Brake
Pinpoint Tests
Pinpoint Test B: The Parking Brake Will Not Release
Normal Operation
When the parking brake control is fully applied and the pedal is pressed a second time, the ratchet mechanism and return spring in the parking brake control cause the tension on the parking brake cables to release. The springs on both rear parking brake cables and the spring on the equalizer provide the force necessary to return the system to the released position.
This pinpoint test is intended to diagnose the following:
- Parking brake cable(s)
- Parking brake control
- Parking brake shoe actuators
- Parking brake shoes and hardware
PINPOINT TEST B: THE PARKING BRAKE WILL NOT RELEASE
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B1 CHECK THE PARKING BRAKE CONTROL
- Press the parking brake control pedal.
- Does the parking brake control move?
Yes
GO to B3.
No
GO to B2.
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B2 ISOLATE THE PARKING BRAKE CONTROL
- Release the parking brake cable tension at the parking brake control adjusting nut.
- Disconnect the parking brake cable at the parking brake lever.
- Press the parking brake control pedal.
- Does the parking brake control move?
Yes
GO to B3.
No
INSTALL a new parking brake control. REFER to Parking Brake Control Service and Repair. TEST the system for normal operation.
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B3 ISOLATE THE FRONT PARKING BRAKE CABLE
- Disconnect the return spring from the equalizer.
- If necessary, relieve the tension in the parking brake cable by loosening the equalizer adjustment nut until the rear cables can be disconnected from the equalizer.
- Disconnect the LH and RH cables from the equalizer.
- Verify that the front cable can slide freely in the conduit.
- Does the cable slide freely in the conduit?
Yes
GO to B4.
No
INSTALL a new front cable. REFER to Parking Brake Cable - Front Parking Brake Cable - Front. TEST the system for normal operation.
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B4 ISOLATE THE REAR PARKING BRAKE CABLES
- Remove the rear parking brake cable-to-support plate bolts and disconnect the rear parking brake cables from their actuators.
- To install, tighten the bolts to 23 Nm (17 lb-ft).
- While holding the cable conduit, attempt to slide the LH and the RH cables inside their conduits.
- Do the cables slide freely inside their conduits?
Yes
GO to B5.
No
INSTALL new rear brake cable(s). REFER to Parking Brake Cable - Rear, LH Parking Brake Cable - Rear, LH and/or Parking Brake Cable - Rear, RH Parking Brake Cable - Rear, RH. TEST the system for normal operation.
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B5 ISOLATE THE PARKING BRAKE SHOE ACTUATORS
- Remove the LH and RH parking brake shoes. Refer to Parking Brake Shoes Service and Repair.
- Attempt to move the LH and RH parking brake shoe actuators by hand.
- Do the actuators move?
Yes
INSTALL new parking brake shoes. REFER to Parking Brake Shoes Service and Repair. TEST the system for normal operation.
No
INSTALL new parking brake shoe actuator(s). REFER to Brake Caliper Support Plate in Disc Brake System. TEST the system for normal operation.
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