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Question

Difficulty: EasyBrake System Components Inspection

To safely and accurately check the free play on manual slack adjusters, what must a driver do before pulling the pushrod by hand?

  1. A
    Keep the parking brakes fully engaged and shut down the engine
  2. Chock the wheels, park on level ground, and release the parking brakesAnswer
  3. C
    Press and hold the service brake pedal down while reading the pushrod markings
  4. D
    Apply the trailer hand control valve while leaving the tractor brakes released

Answer

Chock the wheels, park on level ground, and release the parking brakes so the pushrod can move freely when pulled by hand.
To verify the mechanical free play of a manual slack adjuster, the foundation brake linkage must be relaxed. Chocking the wheels ensures the vehicle cannot roll, and releasing the parking brakes allows the driver to pull the pushrod by hand to confirm it moves no more than about 1 inch.

Step-by-Step Solution

1
Secure the vehicle against rolling on level ground by placing wheel chocks firmly against the tires.
The commercial vehicle is physically secured from moving without relying on mechanical brakes.
Releasing parking brakes without chocks creates a serious runaway hazard.
2
Release the parking brakes from inside the cab to disengage the spring brake chambers.
Air pressure releases the spring tension holding the foundation brake components.
If parking brakes remain set, the pushrods are held rigid and manual slack adjuster free play cannot be physically checked.
3
Pull firmly on each slack adjuster pushrod by hand to check travel distance.
The pushrod moves freely up to the adjustment limit (typically no more than about 1 inch on manual slack adjusters).
This verifies proper stroke adjustment and confirms the brake linkage is neither seized nor excessively worn.

Key Concept

Manual Slack Adjuster Inspection Procedure
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Topics

Brake System Components Inspection

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