CDL Air Brakes TestAir Brake System PartsHard
A driver is inspecting a truck and finds that the front brake limiting valve is set to 'low pressure' mode. Under what conditions should this setting typically be used?
- AWhen performing a pre-trip inspection.
- BWhen driving on slippery surfaces.
- CWhen the vehicle is heavily loaded.
- DWhen driving on dry, paved roads.
Show answer & explanationAnswer & explanation
Correct answer: B. When driving on slippery surfaces.
The front brake limiting valve, found on older vehicles, reduces air pressure to the front brakes by about half. This was intended for use on slippery surfaces to reduce the risk of front-wheel lock-up, which could lead to loss of steering control. Modern ABS systems have largely made this manual valve obsolete.
Why the other options are wrong
- A. The valve setting is for driving conditions, not for inspection procedures.
- C. Heavy loads require more braking power, making 'low pressure' mode unsuitable.
- D. On dry roads, full front braking power is generally desired, so 'normal' pressure would be used.
Front Brake Limiting Valve
An older system component that allows the driver to reduce air pressure to the front brakes by about half, primarily to prevent front wheel lock-up and loss of steering control on slippery surfaces.
- Found on older vehicles without ABS.
- Reduces front brake pressure by approximately 50%.
- Should be used with caution and primarily on slippery roads.
Memory trick: Slippery roads, gentle front brakes.