Automobile & Light Truck Certification Test A5 BrakesMachiningEasy
A technician is machining a brake drum. The drum has a maximum diameter specification of 250.0 mm. After machining, the technician measures the drum at 250.2 mm. What is the MOST appropriate action for the technician to take?
- ALightly sand the drum surface to remove the excess material.
- BRe-machine the drum to bring it within specifications.
- CInstall the drum back on the vehicle as the difference is negligible.
- DDiscard the drum and replace it with a new one.
Show answer & explanationAnswer & explanation
Correct answer: D. Discard the drum and replace it with a new one.
Machining a brake drum past its maximum diameter specification compromises its structural integrity and can lead to brake failure. Discarding and replacing it is the only safe option.
Why the other options are wrong
- A. Sanding will not remove 0.2 mm of material evenly or safely, and the drum is already oversized.
- B. Re-machining would further thin the drum walls, making it even more dangerous and out of specification.
- C. The difference of 0.2 mm is critical when exceeding maximum diameter, as it indicates the drum is unsafe.
Brake Drum Maximum Diameter
The largest allowable internal diameter for a brake drum, typically stamped on the drum itself, beyond which the drum must be replaced for safety.
- Exceeding this limit compromises drum strength.
- Results in reduced braking effectiveness and potential failure.
- Always replace drums that exceed this specification.
Memory trick: Don't cross the red line, or your brakes will decline!