CDL General Knowledge TestDriving SafelyHard
During a pre-trip inspection, a commercial driver notices that the brake adjustment rods (pushrods) on several air brake chambers extend more than 2 inches when the brakes are fully applied. What does this indicate?
- AThe slack adjusters are properly lubricated.
- BThe brakes are out of adjustment and need attention.
- CThe air compressor is over-pressurizing the system.
- DThe brakes are correctly adjusted.
Show answer & explanationAnswer & explanation
Correct answer: B. The brakes are out of adjustment and need attention.
Excessive pushrod travel (more than 2 inches for most types of air brakes) indicates that the brakes are out of adjustment. This means the slack adjusters are not correctly compensating for brake lining wear, leading to reduced braking effectiveness and potential safety hazards. Correctly adjusted brakes would have less travel, lubrication is unrelated to travel distance, and compressor issues would affect pressure, not pushrod length.
Why the other options are wrong
- A. Slack adjuster lubrication is important for proper function, but it does not directly indicate whether the brakes are in adjustment.
- C. An over-pressurizing air compressor would affect the system's air pressure, not the physical travel distance of the brake pushrods during application.
- D. Correctly adjusted brakes will have minimal pushrod travel, typically less than 2 inches, not more.
Excessive Brake Pushrod Travel
A condition in air brake systems where the pushrod extends too far when the brakes are applied, indicating that the brakes are out of adjustment.
- Typically, more than 2 inches of travel is excessive.
- Means the slack adjusters are not compensating for wear.
- Leads to reduced braking effectiveness and potential brake fade.
Memory trick: Pushrod too long, brakes feel wrong, time to tighten, make them strong.