CDL Air Brakes TestInspecting Air Brake SystemsMedium
A driver is conducting a pre-trip inspection. After fully charging the air system (125 psi), the engine is turned off, and the parking brake is released. The driver then applies the service brake fully for one minute. What is the maximum allowable air pressure drop for a combination vehicle during this test?
- A1 psi
- B3 psi
- C4 psi
- D2 psi
Show answer & explanationAnswer & explanation
Correct answer: C. 4 psi
For a combination vehicle, the maximum allowable air pressure drop during the applied service brake test is 4 psi in one minute. This test checks for leaks in the service brake system.
Why the other options are wrong
- A. 1 psi drop is for a straight truck or bus, not a combination vehicle.
- B. 3 psi drop is not a standard maximum for this specific test on a combination vehicle.
- D. 2 psi drop is for a straight truck or bus with the parking brake off, but not a combination vehicle.
Applied Service Brake Leak Test (Combination Vehicle)
A test to check for air leaks in the service brake system of a combination vehicle by applying the foot brake for one minute and observing the pressure drop.
- Combination vehicle: Max 4 psi drop in 1 minute.
- Straight truck/bus: Max 3 psi drop in 1 minute.
- Performed after charging system and releasing parking brake.
Memory trick: Combination four, no leaks or more!