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 out too far when the brakes are applied. What does this indicate?
- AThe air compressor is not building enough pressure.
- BThe slack adjusters are improperly adjusted or faulty.
- CThe brake linings are worn too thin and need replacement.
- DThe brake drums are cracked and expanding excessively.
Show answer & explanationAnswer & explanation
Correct answer: B. The slack adjusters are improperly adjusted or faulty.
Excessive pushrod travel indicates that the slack adjusters are either out of adjustment or faulty. Slack adjusters are designed to maintain the correct gap between the brake linings and the drum/rotor. If they allow too much travel, the brakes won't apply with full force, leading to reduced braking ability.
Why the other options are wrong
- A. Low air pressure would affect overall brake application but not specifically cause excessive pushrod travel when brakes are applied.
- C. While worn linings contribute to longer pushrod travel, the immediate cause of 'too far' travel is usually slack adjuster issue.
- D. Cracked drums are a serious issue, but excessive pushrod travel is more directly related to slack adjuster function, not drum expansion.
Excessive Brake Pushrod Travel
A condition in air brake systems where the pushrod extends beyond its safe limit when the brakes are applied, indicating improper slack adjuster adjustment or failure, compromising braking effectiveness.
- Indicates slack adjuster issue.
- Reduces braking force.
- Increases stopping distance.
- A major safety defect requiring repair.
Memory trick: Pushrod long? Slack adjuster's wrong!