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Difficulty: MediumBrake System Components Inspection

A commercial driver is preparing to verify the mechanical condition and free play of manual slack adjusters during a pre-trip inspection. In what chronological sequence should the driver perform these inspection steps?

  1. 1Chock the vehicle wheels securely on level ground.
  2. 2Release the parking brakes by pushing in the cab supply valves.
  3. 3Pull firmly on each manual slack adjuster using a pry bar or gloved hand.
  4. 4Measure the pushrod stroke distance to ensure free play does not exceed one inch.

Answer

The proper inspection order begins with securing the vehicle with wheel chocks, releasing the parking brakes, pulling the slack adjuster with a pry bar, and finally measuring the pushrod movement to confirm it does not exceed one inch.
The vehicle must first be secured with wheel chocks before releasing the parking brakes to prevent rolling. Releasing the parking brakes relieves spring tension so the pushrod can move. The driver then manually pulls the slack adjuster using a pry bar and measures the resulting pushrod stroke to verify it is within the legal one-inch free play tolerance.

Step-by-Step Solution

1
Place wheel chocks around the tires while parked on level ground.
The combination vehicle is mechanically restrained from accidental movement.
Releasing spring brakes on an unchocked vehicle creates an extreme roll hazard.
2
Disengage the parking and emergency brakes from inside the cab.
Air pressure holds back the spring brakes, taking mechanical clamping tension off the pushrod.
Pushrod free play cannot be physically tested while spring brakes remain applied.
3
Grasp the slack adjuster with a gloved hand or pry bar and pull vigorously away from the brake chamber.
The pushrod extends outward to the limit of its mechanical clearance.
Manual leverage reveals internal mechanical lash between the pushrod clevis and brake shoes.
4
Measure the travel distance between the chamber face and the pushrod marking.
The exact free play measurement is determined and compared against the maximum allowable threshold.
Manual slack adjusters with more than one inch of pushrod movement require immediate adjustment before operating.

Key Concept

Manual Slack Adjuster Pushrod Free Play Inspection Procedure
Estimated Time:1m 15s
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Topics

Brake System Components Inspection

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