Home › CDL Practice Tests › Air Brakes Questions › Question 8
What happens inside an S-cam drum brake when the S-cam rotates?
- A.The drum expands away from the shoes
- B.The ends of the brake shoes are spread apart and pressed against the inside of the drum
- C.The lining is pulled away from the drum
- D.Air is released from the reservoir
Correct answer
B. The ends of the brake shoes are spread apart and pressed against the inside of the drum
Why
The S-shaped cam sits between the shoe ends, so rotation wedges the shoes outward into the drum. The resulting friction is what slows the wheel, and worn linings or excess stroke reduce that contact.
Manual topic: Air Brakes - Air Brake System Components · From the Air Brakes practice bank (AB-008).