Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairEasy
A customer complains of a grinding noise and reduced braking effectiveness from the rear wheels. Upon inspection, a technician finds severe grooves and scoring on the inner surface of the brake drums. What is the MOST likely cause of this condition?
- AWorn-out brake shoes with exposed rivets or metal.
- BContaminated brake fluid in the wheel cylinders.
- COver-adjusted parking brake cable.
- DWeakened brake shoe return springs.
Show answer & explanationAnswer & explanation
Correct answer: A. Worn-out brake shoes with exposed rivets or metal.
Severe grooves and scoring on brake drums are typically caused by direct metal-to-metal contact. This occurs when the friction material of the brake shoes is completely worn away, allowing the shoe's metal backing plate or rivets to rub against the drum.
Why the other options are wrong
- B. Contaminated brake fluid primarily affects hydraulic function and pedal feel, not direct mechanical scoring of the drum.
- C. An over-adjusted parking brake cable would cause dragging or premature wear, not necessarily severe scoring.
- D. Weakened return springs could cause shoes to drag, leading to overheating or uneven wear, but not typically severe scoring unless the shoes were also worn out.
Brake Drum Scoring Cause
Brake drum scoring and grooving are often caused by the metal components of worn brake shoes (rivets, backing plates) directly contacting the drum surface.
- Metal-to-metal contact
- Reduced braking performance
- Grinding noise
Memory trick: When the pads are gone, the metal grinds the drum.