Home › CDL Practice Tests › Air Brakes Questions › Question 2
In a dual air brake system, what does the primary system typically control?
- A.Only the trailer parking brakes
- B.Only the front steering axle brakes
- C.The service brakes on the rear drive axles
- D.The horn and the air suspension only
Correct answer
C. The service brakes on the rear drive axles
Why
In most dual systems the primary circuit operates the rear service brakes, while the secondary circuit operates the front axle. Keeping the circuits separate is what preserves some braking if one side develops a leak.
Manual topic: Air Brakes - Dual Air Brake Systems · From the Air Brakes practice bank (AB-002).