CDL Air Brakes TestInspecting Air Brake SystemsHard
During a pre-trip inspection, a driver observes that the brake pushrod on a service brake chamber extends by 1 1/2 inches when the service brakes are fully applied. The brake chamber is a Type 30. What does this indicate?
- AThe brake is over-adjusted and requires loosening.
- BThe brake is properly adjusted and within limits.
- CThe brake is out of adjustment and needs to be tightened.
- DThe brake chamber diaphragm is ruptured and needs replacement.
Show answer & explanationAnswer & explanation
Correct answer: C. The brake is out of adjustment and needs to be tightened.
A Type 30 brake chamber has a maximum allowable pushrod travel of 2 inches. If the pushrod extends 1 1/2 inches, it is still within the maximum limit, but it's close and indicates the brake is out of adjustment and needs to be tightened to ensure optimal braking performance and to prevent exceeding the limit during normal operation.
Why the other options are wrong
- A. Over-adjustment would result in very short pushrod travel or brakes dragging.
- B. While within the absolute maximum, 1 1/2 inches for a Type 30 is at the higher end, suggesting it's not 'properly adjusted' for optimal performance, but rather 'out of adjustment'.
- D. A ruptured diaphragm would cause air to leak and the brake to not apply or apply very weakly, not necessarily just excessive pushrod travel.
Brake Pushrod Travel (Type 30)
For a Type 30 brake chamber, the maximum allowable pushrod travel is 2 inches. Optimal adjustment aims for less travel, typically around 1 to 1.25 inches.
- Type 30 chamber: Max travel 2 inches.
- Excessive travel indicates maladjustment.
- Maladjustment reduces braking efficiency and increases stopping distance.
Memory trick: Pushrod's reach, know its limit, 2 inches for a Type 30, don't miss it!