Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A technician is performing a pre-inspection of a drum brake system. They notice significant rust and corrosion on the brake drum's friction surface, but no deep scoring or cracking. The drum measures well within its maximum diameter specification. What is the MOST appropriate action to take?
- ALightly sand the friction surface to remove the rust and reinstall.
- BReplace the drum due to the presence of rust and corrosion.
- CMachine the drum to remove the rust and corrosion, ensuring it stays within specifications.
- DApply a rust-inhibiting coating to the drum surface and reinstall.
Show answer & explanationAnswer & explanation
Correct answer: C. Machine the drum to remove the rust and corrosion, ensuring it stays within specifications.
Significant rust and corrosion on the friction surface can cause noise, pulsation, and reduced braking effectiveness. While light surface rust can be sanded, significant corrosion requires machining to create a smooth, clean friction surface for the brake shoes to contact, provided the drum remains within its maximum allowable diameter after machining.
Why the other options are wrong
- A. Light sanding may not remove significant corrosion and could leave an uneven surface.
- B. Replacement is unnecessary if the drum is otherwise sound and can be machined within limits.
- D. Applying a coating would impair braking performance and is not a repair for friction surfaces.
Brake Drum Surface Rust
Corrosion on the brake drum's friction surface that, if significant, can cause noise and uneven braking.
- Caused by moisture exposure.
- Affects braking performance.
- Can be machined if within limits.
Memory trick: Rust on drum, machine it, become a braking chum.