A commercial vehicle with a dual air brake system has its primary system responsible for the rear axle brakes and the secondary system for the front axle brakes. If the primary system experiences a complete failure, what is the immediate consequence for the driver?
- AAutomatic engagement of the parking brake.
- BThe air compressor will stop working.
- CLoss of rear axle braking, but front axle braking remains available.
- DTotal loss of all braking capability.
Show answer & explanationAnswer & explanation
Correct answer: C. Loss of rear axle braking, but front axle braking remains available.
The fundamental purpose of a dual air brake system is redundancy. If one system (e.g., primary, controlling rear brakes) fails, the other system (secondary, controlling front brakes) remains functional, allowing the driver to retain partial braking capability. Total loss of braking would only occur if both systems failed, or if the single system in a non-dual setup failed. The parking brake will eventually engage if air pressure drops too low, but not immediately upon partial system failure. The compressor operates until cut-out or if it fails.
Why the other options are wrong
- A. The parking brake engages when overall system pressure drops significantly, not just one system failure.
- B. The compressor's operation is independent of a single system's failure, as long as it has air to compress.
- D. This contradicts the purpose of a dual air system; partial braking should remain.
Dual System Partial Failure
The scenario where one of the two independent air brake systems in a commercial vehicle fails, resulting in the loss of braking for the axles controlled by that system, while the other system remains functional.
- The vehicle retains partial braking capability.
- A low air pressure warning will activate.
- Requires immediate and careful driving action.
Memory trick: One system down means half the brakes, still enough to slow.