Question

How can you check to see if the spring brakes are operating properly?

Accepted Answer

Chock the wheels, release the parking brakes (press in the yellow knob), and shut the engine off.    
Step on and off the brake pedal to release the air pressure built up in the system.    
The parking brake or spring brakes should automatically come on when the air pressure falls to between 20-45 PSI.    
The knob on the dash will pop out if they are working properly.

Flashcard 8 - Air Brakes Flashcard Set for the CDL

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