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Difficulty: MediumBrake System Components Inspection

To accurately measure pushrod free play on an S-cam air brake assembly equipped with manual slack adjusters, how must the vehicle be configured and tested?

  1. A
    Apply the parking brakes fully, leave the wheels unchocked, and pry the slack adjuster outward to verify zero movement.
  2. Chock the wheels, release the parking brakes, and pull firmly on each slack adjuster by hand to verify it moves no more than about 1 inch.Answer
  3. C
    Set the tractor parking valve, run the engine at high idle, and verify that the angle between the pushrod and adjuster arm remains strictly at 45 degrees.
  4. D
    Keep the parking brakes released on an incline without wheel chocks, press the service brake pedal halfway, and check for up to 2 inches of free play.

Answer

Chock the wheels, release the parking brakes, and pull firmly on each slack adjuster by hand to verify it moves no more than about 1 inch.
To verify pushrod free play on manual slack adjusters, the vehicle must first be secured with wheel chocks so the parking brakes can be safely released. With the spring brakes released, pulling firmly on the slack adjuster by hand should produce no more than approximately 1 inch of pushrod travel where it connects to the slack adjuster arm.

Step-by-Step Solution

1
Secure the vehicle on level ground using wheel chocks.
The vehicle is mechanically prevented from rolling.
The parking brakes must be released during testing, requiring wheel chocks to prevent unintended vehicle movement.
2
Release the parking (spring) brakes from inside the cab.
Air pressure compresses the power spring inside the brake chamber.
Releasing spring brake tension removes clamping force on the foundation brake components, allowing manual movement of the pushrod and slack adjuster.
3
Use a gloved hand or pry bar to pull each slack adjuster away from the brake chamber.
The pushrod stroke travel distance is measured at the clevis pin.
If a manual slack adjuster moves more than approximately 1 inch (2.54 cm2.54\text{ cm}), the brake assembly is out of adjustment and requires mechanical service.

Key Concept

Manual slack adjuster pushrod free play inspection protocol and safety setup
Estimated Time:1m 0s
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Topics

Brake System Components Inspection

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