Practice question

The parking brake control

  1. Lets the air out of the brake chamber
  2. Applies extra pressure to brakes
  3. Locks the wheels
  4. Increases air pressure

Answer: A — Lets the air out of the brake chamber

In air brake systems, the parking brake is a spring-applied, air-released setup. The parking brake control is used to dump air from the brake chambers. When air is released, the energy stored in the springs causes them to clamp the brake shoes onto the drums, holding the wheels and keeping the vehicle from moving. That’s why letting air out of the brake chambers is the function described here. It doesn’t increase air pressure or apply extra service-brake pressure, and it doesn’t “lock” the wheels directly—the result is the spring force holding the brakes on once air is released.

Practice more: Alabama CDL General Practice Test →