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 A5.

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A2 CHECK FOR BROKEN CABLES


- WARNING: Before servicing a vehicle equipped with a fire suppression system, depower the system by following the procedure in Fire Suppression System. Failure to follow the instructions may result in serious personal injury Procedures.

- NOTE: Have an assistant press and release the parking brake pedal to help isolate disconnected cables or cables that do not move.

- Inspect the following items for damage and correct connections:

- Front cable and conduit
- LH rear cable and conduit
- RH rear cable and conduit
- Rear cable brackets
- Are the cables in good condition?

Yes
GO to A3.

No
CONNECT the cable(s) or INSTALL new parking brake component(s) as necessary. TEST the system for normal operation. If equipped with a fire suppression system, GO to A8.

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A3 CHECK THE PARKING BRAKE SHOES, ACTUATOR LEVERS AND HARDWARE


- Remove the rear brake disc, refer to Rear Disc Brake Brake Disc. Inspect the parking brake shoes, actuator levers and hardware.
- Are the parking brake shoes, actuator levers and hardware in good condition?

Yes
GO to A4.

No
INSTALL new components as necessary. REFER to Parking Brake Shoes Service and Repair. TEST the system for normal operation. If equipped with a fire suppression system, GO to A8.

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A4 CHECK THE PARKING BRAKE SHOE ADJUSTMENT


- Check the parking brake shoe adjustment. Refer to Parking Brake Shoe Adjustment Adjustments.
- Are the parking brake shoes adjusted to specification?

Yes
INSTALL a new parking brake control. REFER to Parking Brake Control Service and Repair. TEST the system for normal operation.If equipped with a fire suppression system, GO to A8.

No
ADJUST the rear parking brake shoes. REFER to Parking Brake Shoe Adjustment Adjustments.If equipped with a fire suppression system, GO to A8.

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A5 ISOLATE THE PARKING BRAKE CONTROL AND FRONT PARKING BRAKE CABLE


- WARNING: Before servicing a vehicle equipped with a fire suppression system, depower the system by following the procedure in Fire Suppression System. Failure to follow the instructions may result in serious personal injury Procedures.

- 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 A6.

No
GO to A7.

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A6 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. If equipped with a fire suppression system, GO to A8.

No
INSTALL new rear brake cable(s). REFER to Parking Brake Cable - Rear Parking Brake Cable - Rear. TEST the system for normal operation. If equipped with a fire suppression system, GO to A8.

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A7 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. If equipped with a fire suppression system, GO to A8.

No
INSTALL a new front parking brake cable. REFER to Parking Brake Cable - Front Parking Brake Cable - Front. TEST the system for normal operation. If equipped with a fire suppression system, GO to A8.

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A8 REPOWER THE FIRE SUPPRESSION SYSTEM


- WARNING: Before servicing a vehicle equipped with a fire suppression system, depower the system by following the procedure in Fire Suppression System. Failure to follow the instructions may result in serious personal injury Procedures.

- Verify that the fire suppression system is repowered. Refer to Fire Suppression System Procedures.
- Is the fire suppression system repowered?

Yes
Fire suppression system repowering is complete.

No
REFER to Fire Suppression System Procedures for fire suppression system depowering and repowering procedure.

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