What holds spring brakes in the released position while you are driving normally?

• A.The weight of the vehicle itself
• B.Air pressure compressing the powerful spring inside the brake chamber
• C.Electrical current from the alternator
• D.A mechanical latch on the brake pedal

Why

Spring brakes are applied by spring force and released by air pressure working against that spring. Lose the air and the springs apply the brakes on their own, which is why they double as parking and emergency brakes.

Manual topic: Air Brakes - Spring Brakes · From the General Knowledge practice bank (GK-107).

Practice this subject as a full test

More Powertrain & Brake System Basics questions

• What does the air compressor governor do once air tank pressure reaches its cut-out setting, which is typically around 125 psi?
• At about what air pressure does the governor cut the compressor back in so the system can rebuild pressure?
• What is the job of the safety valve fitted to the first air tank reached by the compressor?
• Why does an air dryer matter to the health of an air brake system?
• Some older air systems use an alcohol evaporator. What problem is it meant to prevent?