Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairHard
A vehicle with drum brakes on the rear experiences a severe pull to one side when the brakes are applied. Upon inspection, the technician finds that the primary brake shoe on the pulling side is heavily glazed and appears overheated, while the secondary shoe on the same wheel appears normal. The wheel cylinder is not leaking. What is the MOST likely cause of this condition?
- AContamination of the primary brake shoe with grease or oil.
- BA weak return spring on the primary shoe side, preventing proper retraction.
- CImproper installation of the primary and secondary shoes.
- DA faulty automatic brake adjuster causing the primary shoe to drag.
Show answer & explanationAnswer & explanation
Correct answer: B. A weak return spring on the primary shoe side, preventing proper retraction.
A weak or broken return spring on the primary shoe would prevent it from retracting fully from the drum when the pedal is released. This would cause continuous light contact (drag) leading to overheating and glazing of that specific shoe, resulting in a pull to that side when the brakes are applied due to uneven braking force.
Why the other options are wrong
- A. Contamination would usually affect both shoes or show as a distinct wet/oily residue, not just glazing from heat.
- C. Improper installation (e.g., shoes reversed) would cause different, more immediate, and severe braking issues.
- D. A faulty adjuster would typically affect both shoes or cause a low pedal, not just one shoe dragging and overheating.
Weak Brake Shoe Return Spring
A weak or broken return spring prevents a brake shoe from fully retracting from the drum, causing continuous drag, overheating, and glazing.
- Causes continuous shoe drag.
- Leads to overheating and glazing.
- Results in brake pull or reduced efficiency.
Memory trick: Spring's weak, shoe can't speak, just drags and makes a streak.