Under normal operation, how is the parking brake engaged in an air brake system?

Under normal operation, how is the parking brake engaged in an air brake system?

• A. Let the air out of the system
• B. Apply the parking brake pedal and hold
• C. Pump the brake pedal
• D. Turn off the engine

Answer: (A)

In an air brake system, the parking brake is spring-applied and air-released. The brakes are held open by air pressure, and when you vent or release that air, the strong springs inside the brake chambers push the brake shoes against the drums, locking the wheels and keeping the vehicle parked. This design makes the parking brake a fail-safe: if the air supply drops, the springs automatically engage.

So letting air out to the brake chambers is how the parking brake engages. Pumping the brake pedal, holding a parking brake pedal, or turning off the engine are not how the parking brake is engaged in normal operation; those actions relate to building service brake pressure or other procedures, not activating the parking brake.