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How is the spring (parking) brake test commonly performed during an air brake check?
- A.Release all air by opening the trailer supply valve at highway speed
- B.Hold the parking brake valve in by hand while driving slowly
- C.With the engine off, fan the brakes to reduce air pressure and confirm the parking brake control pops out and the spring brakes apply on their own in the low-pressure range
- D.Disconnect the emergency line and drive around the lot
Correct answer
C. With the engine off, fan the brakes to reduce air pressure and confirm the parking brake control pops out and the spring brakes apply on their own in the low-pressure range
Why
Spring brakes are held off by air pressure, so losing that pressure must apply them automatically. Fanning the system down verifies that fail-safe action and shows the approximate pressure where the control pops out.
Manual topic: Air Brakes - Brake Inspection · From the Air Brakes practice bank (AB-133).