ASE G1 Auto Maintenance and Light RepairBrakesMedium
A vehicle's parking brake system uses a cable-actuated drum-in-hat design on the rear wheels. The customer complains that the parking brake does not hold the vehicle effectively, even when pulled up all the way. A technician inspects the system and finds no broken cables or seized components. What is the MOST likely cause of this issue?
- AA faulty master cylinder affecting parking brake pressure.
- BWorn parking brake shoes or stretched parking brake cables.
- COver-adjusted rear disc brake calipers.
- DContaminated brake fluid in the hydraulic system.
Show answer & explanationAnswer & explanation
Correct answer: B. Worn parking brake shoes or stretched parking brake cables.
If the parking brake does not hold effectively and the cables aren't broken or seized, the most common causes are worn parking brake shoes within the drum-in-hat assembly or stretched parking brake cables. Both conditions would prevent the shoes from applying sufficient force to hold the vehicle.
Why the other options are wrong
- A. The parking brake system is mechanical (cable-actuated) and separate from the main hydraulic master cylinder, so a faulty master cylinder would not affect it.
- C. Over-adjusted rear disc brake calipers would affect the service brakes, not the separate drum-in-hat parking brake system.
- D. Contaminated brake fluid affects the hydraulic service brake system, not the mechanical parking brake.
Parking Brake Adjustment
Parking brake effectiveness relies on proper adjustment, sufficient shoe lining, and un-stretched cables to ensure adequate holding force.
- Mechanical operation, separate from hydraulics
- Worn shoes reduce holding power
- Stretched cables prevent full engagement
Memory trick: Shoes or cables worn, the parking brake is forlorn.