Brake drums or discs that have cracks larger than ___ the width of the friction area should be replaced:
Correct. Cracks longer than one-half the width of the friction area indicate the drum is unsafe and must be replaced.
CDL Practice Question #152
Category: Air Brakes
Why this question matters
This question is one of 71 in our Air Brakes bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.