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. 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. 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 number 1 from the dimension in measurement number 2.

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 Normal Wear, Eaton

1. Block the wheels.
2. Cage the rear air brake chambers. Refer to Caging the Rear Air Brake Chamber .
3. Raise the vehicle and support the vehicle with safety stands. Refer to Lifting and Jacking the Vehicle in General Information.
4. Turn the air brake automatic slack adjuster adjusting hex clockwise until the brake linings contact the brake drum.
5. Rotate the air brake automatic slack adjuster adjusting hex counterclockwise 180 degrees (1/2  turn).

A minimum of 17.62 N·m (13 lb ft) is necessary in order to overcome the clutch. You will hear a racheting sound.

6. Measure the air brake chamber pushrod stroke. Refer to Air Drum Brake Adjustment .
7. Repeat Steps 4-6 on each wheel until all of the brakes are adjusted.
8. Lower the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
9. Uncage the rear air brake chambers. Refer to Caging the Rear Air Brake Chamber .
10. Check for proper brake operation.
11. Apply the parking brake.
12. Remove the wheel blocks.

Air Drum Brake Adjustment Normal Wear, Rock Slack

1. Block the wheels.
2. Cage the rear air brake chambers. Refer to Caging the Rear Air Brake Chamber .
3. Raise and support the vehicle with safety stands. Refer to Lifting and Jacking the Vehicle in General Information.
4. Adjust the brakes using the following steps:

4.1.	Disengage the pawl assembly with a screwdriver.

4.2.	Turn the air brake automatic slack adjuster adjusting nut until the brake linings contact the brake drum.

4.3.	Rotate the air brake automatic slack adjuster adjusting nut 180 degrees (½ turn).

5. Release the pawl.
6. Measure the air brake chamber pushrod stroke. Refer to Air Drum Brake Adjustment .
7. Repeat Steps 4-5 on each wheel until all of the brakes have been adjusted.
8. Lower the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
9. Uncage the rear air brake chambers. Refer to Caging the Rear Air Brake Chamber .
10. Check for proper brake operation.
11. Apply the parking brake.
12. Remove the wheel blocks.