CDL Air Brakes TestAir Brake System PartsMedium
A driver is inspecting a commercial vehicle and observes that the front brake limiting valve is stuck in the 'slippery' position. What effect will this have on the vehicle's braking performance?
- AReduced braking power to the front wheels.
- BNo effect on braking performance, as it's an emergency setting.
- CAutomatic engagement of the parking brake when driving.
- DIncreased braking power to the front wheels.
Show answer & explanationAnswer & explanation
Correct answer: A. Reduced braking power to the front wheels.
The front brake limiting valve, when set to the 'slippery' position, reduces the air pressure applied to the front service brake chambers by about half. This is intended for slippery conditions to prevent front wheel lock-up. If stuck in this position, it will continuously reduce front braking power, even in normal conditions.
Why the other options are wrong
- B. It has a significant effect, potentially increasing stopping distances in normal conditions or causing imbalance.
- C. The front brake limiting valve affects service brakes, not the parking brake engagement.
- D. The 'slippery' position is designed to prevent front wheel lock-up by reducing, not increasing, front braking power.
Front Brake Limiting Valve
A valve found on some older vehicles that allows the driver to reduce air pressure to the front brakes (e.g., by half) for driving on slippery surfaces.
- Typically has 'normal' and 'slippery' (or 'low') settings.
- Reduces front braking power in 'slippery' mode.
- Should be in 'normal' for most driving conditions.
Memory trick: Slippery Setting = Soft Front Stop.