Home › CDL Practice Tests › Air Brakes Questions › Question 29
If the air pressure in both dual circuits drops very low, what additional system is designed to stop the vehicle automatically?
- A.The air conditioning clutch
- B.The retarder in its lowest setting only
- C.The spring brakes, which apply mechanically as air pressure is lost
- D.The trailer breakaway cable alone
Correct answer
C. The spring brakes, which apply mechanically as air pressure is lost
Why
Spring brakes are held off by air pressure, so a serious loss of air lets the springs apply the brakes on their own. That fail-safe design is why total air loss still ends with the vehicle stopping rather than rolling free.
Manual topic: Air Brakes - Dual Air Brake Systems · From the Air Brakes practice bank (AB-029).