CDL General Knowledge TestAir Brakes (if applicable)Hard
A technician is troubleshooting a dual air brake system where the primary (rear axle) air tank pressure consistently drops faster than the secondary (front axle) air tank pressure during a static leakage test. What is the most likely area to investigate first?
- AThe air compressor governor settings.
- BThe air lines and brake chambers associated with the rear axles.
- CThe air dryer's purge valve.
- DThe front axle's brake adjustment.
Show answer & explanationAnswer & explanation
Correct answer: B. The air lines and brake chambers associated with the rear axles.
If the primary (rear axle) air tank is losing pressure faster, it indicates a leak in the portion of the system supplied by that tank. The most common components in this circuit that could leak are the air lines and brake chambers for the rear axles. Investigating these components first will likely identify the source of the rapid pressure drop.
Why the other options are wrong
- A. Governor settings affect cut-in/cut-out, not differential leak rates between tanks.
- C. The air dryer purge valve affects overall system moisture and air loss during purging, not a differential leak between primary and secondary tanks during a static test.
- D. Front axle brake adjustment would affect front braking, not the primary tank's leak rate.
Dual Air System Differential Leak
If one air tank in a dual air brake system loses pressure faster than the other during a static test, the leak is likely in the components supplied by that tank.
- Primary tank supplies rear brakes.
- Secondary tank supplies front brakes.
- Rapid drop indicates a leak in its circuit.
- Focus investigation on relevant components.
Memory trick: Primary drops, rear brakes are the cause, check those lines without pause.