CDL Air Brakes TestInspecting Air Brake SystemsMedium
A driver is performing a pre-trip inspection on a vehicle equipped with automatic slack adjusters. Which of the following is the correct procedure for checking the adjustment of these slack adjusters?
- ADrain all air from the system, then visually inspect the slack adjuster for excessive movement.
- BManually turn the adjusting nut until the pushrod travel is within limits, then recheck.
- CApply the parking brake and attempt to rock the vehicle back and forth to check for play.
- DEnsure the air system is fully charged, then make multiple full brake applications and visually check pushrod travel.
Show answer & explanationAnswer & explanation
Correct answer: D. Ensure the air system is fully charged, then make multiple full brake applications and visually check pushrod travel.
Automatic slack adjusters are designed to adjust themselves during normal brake applications. To check their adjustment, the air system should be fully charged, and then several hard brake applications should be made. If the pushrod travel is still excessive after this, the slack adjuster is likely faulty and needs repair, not manual adjustment.
Why the other options are wrong
- A. Draining air and inspecting for movement is not the primary way to check automatic slack adjuster adjustment.
- B. Manually adjusting automatic slack adjusters is generally discouraged and can damage them or mask underlying issues.
- C. Rocking the vehicle checks the parking brake holding ability, not the adjustment of service brake slack adjusters.
Automatic Slack Adjuster Check
The procedure to verify the proper functioning and adjustment of automatic slack adjusters without manual intervention.
- Do NOT manually adjust automatic slack adjusters.
- Check by making multiple full brake applications.
- Observe pushrod travel; if excessive, adjuster is faulty.
- Air system must be fully charged for the check.
Memory trick: Auto-adjust? Full air, hard press, then assess!