Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairEasy
A technician is diagnosing a drum brake system where the parking brake lever moves through its full travel without engaging the brakes effectively. What is the MOST likely cause?
- AWorn brake shoe linings
- BContaminated brake shoes
- CSeized wheel cylinders
- DExcessive parking brake cable slack
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive parking brake cable slack
If the parking brake lever moves through its full travel without engaging the brakes, it indicates that the cable is not effectively transmitting force to the brake shoes. Excessive slack in the parking brake cable is the most common reason for this symptom, preventing the shoes from expanding against the drum.
Why the other options are wrong
- A. While worn linings contribute to poor braking, excessive lever travel specifically points to cable slack.
- B. Contaminated brake shoes would reduce friction but not cause the lever to travel through its full range without engagement.
- C. Seized wheel cylinders affect hydraulic braking, not typically the mechanical parking brake.
Parking Brake Cable Slack
Excessive play or looseness in the parking brake cable, preventing effective engagement of the parking brake mechanism.
- Causes parking brake lever to travel too far
- Results in poor or no parking brake holding force
- Requires adjustment or cable replacement
Memory trick: Slack cable, no brake snack.