CDL Combination Vehicles TestInspecting Combination VehiclesHard
During a pre-trip inspection of a combination vehicle, you are checking the brake adjustment. The pushrod on a cam-type brake with a 6-inch brake chamber moves 1.5 inches when the brakes are applied. What does this indicate?
- AThe slack adjuster is over-lubricated.
- BThe brakes are correctly adjusted.
- CThe brake lining is too thin and requires replacement.
- DThe brakes are out of adjustment and need attention.
Show answer & explanationAnswer & explanation
Correct answer: D. The brakes are out of adjustment and need attention.
For a Type 6 brake chamber, the maximum allowable pushrod travel before adjustment is 1 inch. A pushrod travel of 1.5 inches significantly exceeds this limit, indicating that the brakes are out of adjustment and require immediate attention to ensure safe braking performance.
Why the other options are wrong
- A. Over-lubrication of the slack adjuster would not directly cause excessive pushrod travel, though it's not ideal.
- B. Correct adjustment for a Type 6 chamber is typically less than 1 inch; 1.5 inches is excessive.
- C. While thin brake lining can contribute to excessive travel, the primary indicator here is the pushrod movement itself, which points to an adjustment issue first.
Brake Pushrod Travel
The distance a brake pushrod moves when the brakes are applied, indicating the adjustment status of the foundation brakes.
- Excessive travel means brakes are out of adjustment.
- Maximum travel limits vary by brake chamber type.
- Out-of-adjustment brakes reduce braking effectiveness.
Memory trick: Pushrod too far, brake's not there!