CDL Combination Vehicles TestCombination Vehicle Air BrakesMedium
A driver is performing a pre-trip inspection on a combination vehicle. After building full air pressure (120 psi), the driver applies the service brakes and holds them for one minute. The air pressure drop should not exceed what amount for a combination vehicle?
- A1 psi
- B3 psi
- C4 psi
- D2 psi
Show answer & explanationAnswer & explanation
Correct answer: C. 4 psi
This question refers to the 'Applied Air Brake Leakage Test'. For a combination vehicle, the air pressure should not drop more than 4 psi in one minute after applying the service brakes, indicating a healthy system without excessive leaks.
Why the other options are wrong
- A. 1 psi is an unnecessarily strict limit; some minor leakage is expected.
- B. 3 psi is a common distractor but not the correct limit for combination vehicles.
- D. 2 psi is the limit for single vehicles, not combination vehicles.
Applied Air Brake Leakage Test (Combination)
A test performed during a pre-trip inspection where the service brakes are applied and held to check for excessive air leakage. For a combination vehicle, the pressure drop should not exceed 4 psi in one minute.
- Tests the integrity of the entire brake system.
- Performed after full air pressure is built.
- Excessive drop indicates a leak requiring repair.
Memory trick: Four wheels on a combination vehicle, so 4 psi is the limit.