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Difficulty: MediumBrake System Components Inspection

A driver is conducting an applied pushrod stroke measurement on a commercial vehicle's air brake chamber to verify foundation brake adjustment. In what sequential order should the driver execute the following procedure?

  1. 1Secure the vehicle with wheel chocks on level ground and release the spring parking brakes.
  2. 2Mark the pushrod with chalk or a marker at the exact point where it exits the brake chamber housing.
  3. 3Have a helper make and hold a full service brake application of 90 to 100 psi.
  4. 4Measure the distance from the chamber housing face to the reference mark on the extended pushrod.
  5. 5Compare the measured stroke against the Commercial Vehicle Safety Alliance (CVSA) out-of-service limit for that chamber size.

Answer

1. Secure the vehicle with wheel chocks on level ground and release the spring parking brakes. 2. Mark the pushrod with chalk or a marker at the exact point where it exits the brake chamber housing. 3. Have a helper make and hold a full service brake application of 90 to 100 psi. 4. Measure the distance from the chamber housing face to the reference mark on the extended pushrod. 5. Compare the measured stroke against the Commercial Vehicle Safety Alliance (CVSA) out-of-service limit for that chamber size.
The correct sequence begins by safely securing the vehicle with chocks and releasing the parking brakes so the pushrod returns to its baseline resting position. A zero-point mark is made where the rod exits the chamber. Next, a full 90 to 100 psi service brake application extends the pushrod. The distance from the chamber housing to the mark is then measured and compared against the maximum legal stroke limit for that specific brake chamber size.

Step-by-Step Solution

1
Chock the wheels and fully release the parking/emergency brakes.
The vehicle is safely held in place while air pressure holds the spring brakes released, allowing the pushrods to fully retract.
Accurate baseline measurement requires the pushrod to be in its completely retracted rest position without spring brake force applied.
2
Place a distinct chalk or pen mark on the pushrod right at the exit point of the chamber face.
A zero-point reference indicator is established.
Without a zero-point reference mark on the retracted rod, total extension travel cannot be accurately measured.
3
Charge the air system and apply 90 to 100 psi of service brake pressure.
Service air pressure forces the diaphragm forward, extending the pushrod and rotating the slack adjuster.
Standard applied stroke testing requires full operational service pressure to seat the brake linings firmly against the drums.
4
Measure the linear displacement from the chamber face to the mark with a ruler.
The exact operating pushrod stroke is obtained in inches or millimeters.
Linear measurement directly determines how far the pushrod travels under full service application.
5
Cross-reference the measured distance with the maximum allowable stroke chart for the specific brake chamber type and size.
A pass/fail determination is made regarding brake adjustment compliance.
Verifying that pushrod travel does not exceed safety thresholds ensures adequate reserve braking power.

Key Concept

Applied pushrod stroke measurement protocol and brake chamber adjustment criteria.
Estimated Time:1m 30s
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Topics

Brake System Components Inspection

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