CDL General Knowledge TestCombination Vehicles (if applicable)Hard
A driver is inspecting the brake chamber pushrods on a combination vehicle. The maximum allowable brake stroke for a Type 30 brake chamber is 2 inches. If the pushrod extends 2.25 inches when the brakes are applied, what does this indicate?
- AThe brake linings are worn and need to be replaced soon.
- BThe brakes are correctly adjusted and operating efficiently.
- CThe slack adjuster needs to be adjusted, or there is a problem with the braking system.
- DThe air compressor is not building enough pressure to fully apply the brakes.
Show answer & explanationAnswer & explanation
Correct answer: C. The slack adjuster needs to be adjusted, or there is a problem with the braking system.
A pushrod stroke exceeding the maximum allowable limit (2 inches for a Type 30 chamber) indicates that the brake is out of adjustment. This could be due to a faulty automatic slack adjuster, worn brake linings, or other issues within the brake system that require immediate attention and repair.
Why the other options are wrong
- A. While worn linings can cause excessive stroke, the immediate indication is maladjustment; replacement is a subsequent step after diagnosis.
- B. A stroke exceeding 2 inches indicates an out-of-adjustment brake, not correct operation.
- D. Insufficient air pressure would affect all brakes, but an individual brake chamber showing excessive stroke points to a specific adjustment or component issue, not just overall pressure.
Excessive Brake Stroke
An excessive brake pushrod stroke indicates the brake is out of adjustment, requiring investigation and repair of the slack adjuster or other brake components.
- Beyond maximum allowed limit.
- Indicates maladjustment.
- Requires immediate repair.
Memory trick: Long stroke, system broke; check the slack, get on track.