Air Drum Brake Adjustment Pushrod Stroke Measurement

Check your maintenance schedule for the recommended service intervals.

Measure the pushrod stroke in order to determine if the brakes are acceptably adjusted (1). The pushrod travel should be less than the maximum allowable stroke listed in the Dimensional Specifications Table. Refer to Air Drum Brake Component Specifications .

The stroke is the difference between the released air brake automatic slack adjuster position and the applied air brake automatic slack adjuster position. The applied position must be measured at 550-620 kPa (80-90 psi) air pressure in the brake chamber assemblies when the brakes are fully applied.

1. Start the engine to increase the air pressure to 690 kPa (100 psi) if necessary.
2. Stop the engine. Apply and release the brakes to decrease the air pressure to 690  kPa (100 psi) if necessary.



3. Check the dual air pressure gauge in order to ensure the correct air pressure. Verify that the air pressure in the air reservoirs is 690 kPa (100 psi) under the following conditions:

•	The engine is OFF

•	The rear air brake chambers, spring brake chamber section, are released

4. For (X) measure the distance between the brake chamber assembly mounting surface and the center of the air brake chamber clevis pin on all of the brakes.
5. Have an assistant apply and hold one full brake application.
6. For (Z) measure the distance between the brake chamber assembly mounting surface and the center of the air brake chamber clevis pin on all of the brakes with the brakes applied at 550-620 kPa (80-90 psi).
7. Release the brakes.
8. Calculate the adjusted air brake chamber stroke at each brake using the following method:

8.1.	Subtract the dimension in measurement (X) from the dimension in measurement (Z).

8.2.	The difference between the two dimensions is the adjusted air brake chamber stroke. The adjusted air brake chamber stroke must not be greater than the stroke length shown in the Dimensional Specifications Table. Refer to Air Drum Brake Component Specifications .

8.3.	Adjust the brakes if the pushrod stroke is greater than the recommended values. Refer to Air Drum Brake Adjustment .

Air Drum Brake Adjustment Arvin-Meritor/Gunite

Check your maintenance schedule for the recommended service intervals.

Measure the pushrod stroke in order to determine if the brakes are acceptably adjusted (1). The pushrod travel should be less than the maximum allowable stroke listed in the Dimensional Specifications Table. Refer to Air Drum Brake Component Specifications .

1. Block the wheels.
2. Perform the Push Rod Stroke Measurement procedure to see if adjustment is needed.




Important: Automatic slack adjusters should never be manually adjusted in an effort to correct excessive chamber pushrod stroke. Manual adjustment of the automatic slack adjuster can result in a degradation of slack adjuster performance over time. If pushrod stroke is out of adjustment, determine root cause of excess stroke by checking the chamber clevis, clevis pins, brake return springs, camshaft bracket, camshaft bushings, and related foundation brake components for wear or damage. Replace any worn or damaged components. Also ensure that the clevis jam nut is not loose. If the pushrod stroke is still out of adjustment, replace the slack adjuster.

3. To adjust the chamber stroke or slack adjuster setting, perform the following:

3.1.	Disengage the pawl (1) by using a flat-bladed tool to lift the button on the pawl assembly at least 1/32 inch.

3.2.	Turn the manual adjustment nut (2) 1/8 turn counterclockwise until the linings touch the drum.

3.3.	Back off the linings by turning the manual adjuster nut (2) a 1/2 turn in the opposite direction.

3.4.	Rotate the drum to check for clearance.

3.5.	Remove the flat-bladed tool from the pawl (1).