Michigan CDL - Air Brakes Practice Exam

What is the maximum allowable crack length on a brake drum during a walk-around inspection?

1. One quarter of the width of the friction area

2. One half of the width of the friction area

3. Three quarters of the width of the friction area

4. Full width of the friction area

The correct answer is: One half of the width of the friction area

The maximum allowable crack length on a brake drum during a walk-around inspection is one half of the width of the friction area. This standard is in place to ensure safe braking performance and structural integrity of the brake components. A crack that exceeds this limit can compromise the drum's ability to effectively absorb heat and withstand the physical stresses experienced during braking. If a crack is allowed to grow larger than this limit, it could lead to catastrophic failure, which poses a serious safety risk. The width of the friction area is significant because it is where the brake shoes make contact with the drum. Maintaining the integrity of this area is crucial for effective braking. Thus, limiting crack length to one half of the friction area provides a balance between safety and the operational lifespan of the drum.