Pinpoint Test A: The Parking Brake Does Not Apply
Parking Brake
Pinpoint Tests
Pinpoint Test A: The Parking Brake Does Not Apply
Normal Operation
When the parking brake control pedal is pressed, the pedal should move a short distance, with more pressure needed to apply the pedal as it gets closer to the floor, until the parking brake shoes are fully applied. When the pedal is pressed, tension is applied to the front parking brake cable. This tension pulls on the LH rear parking brake cable, which is attached to the LH rear parking brake shoe actuator and applies the LH rear brake shoes. At the same time, the tension in the LH rear cable causes the LH rear cable conduit to attempt to straighten out. This straightening effect causes the LH rear cable conduit to pull on the RH rear parking brake cable, which is attached to the RH rear parking brake shoe actuator and applies the RH rear brake shoes.
This pinpoint test is intended to diagnose the following:
- Rear parking brake cables and conduits
- Front parking brake cable and conduit
- Parking brake shoes and hardware
- Parking brake control
PINPOINT TEST A: THE PARKING BRAKE DOES NOT APPLY
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A1 CHECK THE PARKING BRAKE CONTROL
- Press the parking brake control pedal.
- Does the parking brake control pedal move?
Yes
GO to A2.
No
GO to A6.
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A2 CHECK FOR BROKEN CABLES
- NOTE: Have an assistant press and release the parking brake pedal to help isolate disconnected cables or cables that do not move.
- Inspect the front cable, both rear cables, cable equalizers and parking brake shoes or brake shoe actuators for damage and correct connections.
- Is any damage found or are any cables disconnected?
Yes
CONNECT the cable(s) or INSTALL new parking brake component(s) as necessary. TEST the system for normal operation.
No
GO to A3.
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A3 CHECK THE PARKING BRAKE CABLE ADJUSTMENT
- Check the parking brake cable adjustment. Refer to Parking Brake Cable Adjustment Adjustments.
- Are the cables out of adjustment?
Yes
ADJUST as necessary. TEST the system for normal operation.
No
GO to A4.
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A4 CHECK THE PARKING BRAKE SHOES AND HARDWARE
- Remove the rear brake disc, refer to Disc Brake System. Inspect the parking brake shoes and hardware for damage and/or missing components.
- Is any damage found or are any components missing?
Yes
INSTALL new components as necessary. REFER to Parking Brake Shoes Service and Repair. TEST the system for normal operation.
No
GO to A5.
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A5 CHECK THE PARKING BRAKE SHOE ADJUSTMENT
- Check the parking brake shoe adjustment. Refer to Parking Brake Shoe Adjustment Adjustments.
- Are the shoes out of adjustment?
Yes
ADJUST as necessary. TEST the system for normal operation.
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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A6 ISOLATE THE PARKING BRAKE CONTROL AND FRONT PARKING BRAKE CABLE
- Disconnect the front parking brake cable from the LH rear parking brake cable.
- Press the parking brake control pedal.
- Does the parking brake control pedal move?
Yes
GO to A7.
No
GO to A8.
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A7 ISOLATE THE REAR PARKING BRAKE CABLES
- Disconnect the rear parking brake cables from the brake shoe actuator cables.
- While holding the cable conduit, attempt to slide the cable inside the conduit.
- Does the cable slide freely inside the conduit?
Yes
INSPECT the parking brake shoes, hardware and backing plate. INSTALL new components as necessary. REFER to Parking Brake Shoes Service and Repair. TEST the system for normal operation.
No
INSTALL new rear brake cable(s). REFER to Parking Brake Cable - Rear Parking Brake Cable - Rear. TEST the system for normal operation.
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A8 ISOLATE THE FRONT PARKING BRAKE CABLE
- Disconnect the front parking brake cable and conduit from the parking brake control.
- While holding the cable conduit, attempt to slide the cable inside the conduit.
- Does the cable slide freely inside the conduit?
Yes
INSTALL a new parking brake control. REFER to Parking Brake Control Service and Repair. TEST the system for normal operation.
No
INSTALL a new front parking brake cable. REFER to Parking Brake Cable - Front Parking Brake Cable - Front. TEST the system for normal operation.
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