Home › CDL Practice Tests › General Knowledge Questions › Question 112
Why does a very hot brake drum stop the vehicle less effectively, even before the linings are damaged?
- A.Heat only changes the color of the drum
- B.Heat increases air pressure in the tanks
- C.Heat makes the drum shrink tightly onto the linings
- D.Heat makes the drum expand outward, away from the brake linings, so contact and friction drop
Correct answer
D. Heat makes the drum expand outward, away from the brake linings, so contact and friction drop
Why
As a drum overheats it grows in diameter, moving its friction surface away from the shoes. The chamber may run out of stroke trying to follow it, which is one part of how overheated brakes lose stopping power on grades.
Manual topic: Air Brakes - Brake Drums · From the General Knowledge practice bank (GK-112).