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Difficulty: MediumBrake System Components Inspection

An operator inspects the foundation air brake components on a commercial combination vehicle. Which of the following findings indicates that a manual slack adjuster is out of adjustment and requires maintenance?

  1. A
    The pushrod extends 1/2 inch from the brake chamber when pulled by hand with the parking brakes released.
  2. B
    Zero pushrod movement is observed when pulled by hand while the spring parking brakes remain fully applied.
  3. Pushrod free play exceeds 1 inch when pulled firmly by hand with the parking brakes disengaged.Answer
  4. D
    The angle between the pushrod and adjuster arm forms approximately 90 degrees when the service brakes are fully applied.

Answer

Pushrod free play exceeding 1 inch when pulled firmly by hand with the parking brakes disengaged indicates an out-of-adjustment condition requiring service.
On commercial vehicles equipped with manual slack adjusters, free play travel of the pushrod should not exceed approximately 1 inch when pulled firmly by hand with the parking brakes released and wheels chocked.

Step-by-Step Solution

1
Determine the proper procedural condition for checking manual slack adjuster free play.
Vehicle must be on level ground with wheels chocked and parking brakes released so the pushrod can move freely.
Keeping the parking brakes applied locks the foundation brake assembly, preventing an accurate free play measurement.
2
Compare observed mechanical tolerances against CDL foundation brake safety thresholds.
Manual slack adjuster pushrod movement must not exceed approximately 1 inch when pulled firmly by hand.
Excessive pushrod stroke causes brake lag, reduced stopping torque, and potential foundation brake failure.

Key Concept

Manual slack adjuster free play inspection threshold
Estimated Time:1m 0s
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Topics

Brake System Components Inspection

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