CDL General Knowledge TestAir Brakes (if applicable)Easy
A truck driver is performing a pre-trip inspection. They notice that when the brake pedal is fully depressed, the pushrod on a service brake chamber moves less than 1 inch. The brakes appear to be working. What is the most likely implication of this observation?
- AThis indicates normal operation for a properly adjusted air brake system.
- BThe slack adjuster is likely out of adjustment, requiring manual adjustment.
- CThe air compressor is not building sufficient pressure to fully actuate the brakes.
- DThe brake linings are likely worn out and need replacement soon.
Show answer & explanationAnswer & explanation
Correct answer: A. This indicates normal operation for a properly adjusted air brake system.
A pushrod travel of less than 1 inch when the brake pedal is fully depressed typically indicates that the slack adjuster is properly adjusted and the brakes are in good working order.
Why the other options are wrong
- B. An out-of-adjustment slack adjuster would typically result in excessive pushrod travel (more than 1 inch), not less.
- C. Insufficient air pressure would lead to weak braking and potentially excessive pushrod travel if the chamber attempts to compensate, or no travel if pressure is too low to engage the brakes at all.
- D. Worn linings would usually result in excessive pushrod travel, not less than 1 inch.
Pushrod Travel Inspection
Checking the distance the pushrod moves out of the brake chamber when the service brakes are applied, indicating slack adjuster adjustment.
- Should be less than 1 inch on most brake types.
- Excessive travel indicates maladjustment or wear.
- Part of pre-trip inspection.
Memory trick: Slack Adjuster: Just Right, Not Too Far, Not Too Close