CDL Combination Vehicles TestCombination Vehicle Air BrakesMedium
When inspecting a combination vehicle's air brake system, you discover that the slack adjusters on several brake chambers move more than one inch when pulled by hand. What is the correct course of action?
- AThe vehicle is unsafe to drive and requires immediate repair/adjustment.
- BThis is normal play for slack adjusters; continue the inspection.
- CRecord the finding and drive cautiously to the nearest service center.
- DAdjust the slack adjusters immediately and recheck their travel.
Show answer & explanationAnswer & explanation
Correct answer: A. The vehicle is unsafe to drive and requires immediate repair/adjustment.
Slack adjusters that move more than one inch (or sometimes 3/4 inch, depending on jurisdiction/manufacturer) indicate that the brakes are out of adjustment. Brakes that are out of adjustment will not brake effectively and can lead to uneven braking, increased stopping distances, and potential brake failure. This is a critical safety defect that renders the vehicle unsafe to drive.
Why the other options are wrong
- B. Excessive slack adjuster movement (more than 1 inch) is NOT normal; it indicates maladjustment.
- C. Driving with brakes out of adjustment is unsafe and illegal. It must be fixed before driving.
- D. While adjustment is needed, the question asks for the 'correct course of action' regarding driving. The vehicle is unsafe *before* adjustment.
Slack Adjuster Inspection
A pre-trip inspection to check the free play or stroke of the slack adjusters on air brakes. Excessive movement (typically more than 1 inch) indicates that the brakes are out of adjustment and require immediate attention.
- Check by pulling on the slack adjuster by hand.
- Movement should not exceed 1 inch (or 3/4 inch, check local regs).
- Out of adjustment brakes are unsafe and must be corrected.
Memory trick: Slack Adjuster Stroke Shows Safety.