Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A technician is diagnosing a drum brake system where the parking brake lever requires excessive pulling and the rear brakes show poor holding power when the parking brake is engaged. They verify the parking brake cable is not seized. What is the MOST likely cause of this condition?
- AContaminated brake shoes.
- BOver-adjusted drum brake shoes.
- CWorn or improperly adjusted parking brake cable.
- DSeized wheel cylinder pistons.
Show answer & explanationAnswer & explanation
Correct answer: C. Worn or improperly adjusted parking brake cable.
Excessive pulling of the parking brake lever and poor holding power are classic symptoms of a parking brake cable that is either worn (stretched) or improperly adjusted. The cable needs to be tightened to take up the slack and ensure proper engagement.
Why the other options are wrong
- A. Contaminated shoes would reduce friction for both service and parking brakes, but cable adjustment is more direct to the 'excessive pulling' symptom.
- B. Over-adjusted shoes would cause drag, not poor parking brake holding.
- D. Seized wheel cylinders would affect service brake operation more directly and prevent shoe movement.
Parking Brake Cable Slack
Excessive slack in the parking brake cable reduces the mechanical advantage, requiring more lever travel to engage the parking brake shoes against the drum.
- Leads to weak parking brake.
- Requires more lever travel.
- Adjustable to restore function.
Memory trick: Cable too long, parking brake's song is weak and wrong.