CDL Air Brakes TestDual Air Brake SystemsMedium
During a road test, a commercial vehicle driver experiences a sudden loss of air pressure in the front axle's brake system. Due to the vehicle's dual air brake system, what would be the immediate consequence for the vehicle's braking capability?
- AThe parking brake will automatically engage to stop the vehicle safely.
- BIncreased braking power in the rear axle to compensate for the front loss.
- CTotal loss of all braking power for the entire vehicle.
- DReduced braking power, primarily affecting the front wheels, with rear wheel braking still functional.
Show answer & explanationAnswer & explanation
Correct answer: D. Reduced braking power, primarily affecting the front wheels, with rear wheel braking still functional.
A dual air brake system separates braking for the front and rear axles. If the front system fails, the rear system (primary) will still provide braking, albeit with reduced overall stopping power and potential steering issues.
Why the other options are wrong
- A. The parking brake is a separate system and does not automatically engage due to a service brake system failure while driving.
- B. The rear axle's braking power does not automatically increase; it continues to function as designed, but the overall vehicle braking is compromised.
- C. This is precisely what a dual system is designed to prevent; it ensures some braking remains.
Dual System Failure Consequence
If one of the two independent air brake systems (primary or secondary) fails, the other system continues to provide partial braking capability.
- Primary system typically controls rear brakes.
- Secondary system typically controls front brakes.
- Failure of one system means loss of braking for its controlled axle(s).
Memory trick: Front brakes gone, rear brakes on, still slow, but not gone.