Air Drum Brake Adjustment Pushrod Stroke Measurement

Refer to Maintenance Schedule in Maintenance and Lubrication.

Measure the pushrod stroke in order to determine if the brakes are acceptably adjusted. 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.
3. Apply and release the brakes to decrease the air pressure to 690  kPa (100 psi) if necessary.



4. Check the duel air pressure gauge in order to ensure that the air pressure in the air reservoirs is 690 kPa (100 psi) with the engine off and that the rear air brake chambers (spring brake chamber section) is released.
5. 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.



6. Have an assistant apply and hold one full brake application.
7. 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).
8. Release the brakes.
9. Calculate the adjusted air brake chamber stroke at each brake.

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

9.2.	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 .

9.3.	Adjust the brakes if the pushrod stroke is greater than the specifications. Refer to Air Drum Brake Adjustment .

Air Drum Brake Adjustment Normal Wear Adjustment

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. Adjust the brakes.

4.1.	Disengage the pawl assembly with a screwdriver.

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

4.3.	Rotate the slack adjuster adjusting nut 180 degrees (1/2 turn).

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

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 slack adjuster adjusting hex clockwise until the brake linings contact the brake drum.
5. Rotate the 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 have been adjusted.
8. Lower the vehicle.
9. Uncage the rear air brake chambers. Refer to Caging the Rear Air Brake Chamber .
10. Check for proper brake operation.
11. Set the parking brake.
12. Remove the wheel blocks.