CDL Air Brakes TestInspecting Air Brake SystemsMedium
A technician is inspecting a vehicle's air brake system and observes that the brake chambers at one axle have significantly different pushrod travel when the service brakes are applied. One chamber shows 1 inch of travel, while the other shows 2.5 inches. The maximum allowable pushrod travel for this type of chamber is 2 inches. What is the most appropriate conclusion?
- AThe difference in travel indicates a problem with the air supply to that axle.
- BThe brake chamber with 2.5 inches of travel is out of adjustment and requires attention.
- CBoth brake chambers are within acceptable limits, but one is less efficient.
- DThe brake chamber with 1 inch of travel is too tight and needs adjustment.
Show answer & explanationAnswer & explanation
Correct answer: B. The brake chamber with 2.5 inches of travel is out of adjustment and requires attention.
The maximum allowable pushrod travel for this type of chamber is 2 inches. A pushrod travel of 2.5 inches exceeds this limit, indicating that the brake is out of adjustment and will not provide proper braking force. The 1-inch travel is within limits.
Why the other options are wrong
- A. Different travel on the same axle suggests a mechanical issue with the brakes themselves, not a general air supply problem.
- C. 2.5 inches is not within acceptable limits.
- D. 1 inch is within the 2-inch limit and does not necessarily indicate it's too tight; it's just well-adjusted.
Brake Pushrod Travel
The distance the pushrod moves out of the brake chamber when the service brakes are applied. Excessive travel indicates improper brake adjustment.
- Measured from the brake chamber to the slack adjuster.
- Indicates how much slack is in the brake system for that wheel.
- Different chambers have different maximum allowable travel, typically 1.5 to 2.5 inches.
- Exceeding maximum travel means the brake is out of adjustment and unsafe.
Memory trick: Pushrod's reach, if too far, puts your safety far afar.