Air Brake Application Valve Operational Check Operational Check

1. Block the wheels.
2. Install accurate test gauges into the front and rear dual application valve circuits.
3. Start the engine.
4. Charge the air system to the air compressor governor cut-out point.
5. Stop the engine.



6. Test the delivery air pressure in both the front circuits and the rear circuits.

6.1.	Depress the brake pedal to several positions between fully released and fully applied.

6.2.	Check the delivered air pressure on the test gauges in order to see that the pressure varies equally and proportionality with the movement of the brake pedal.

After you release a full brake application, verify that the reading on the test gauges falls off to zero promptly. With both service air reservoirs at the same pressure, the rear brake circuit delivery air pressure will be about 14 kPa (2 psi) greater than the front brake delivery air pressure. This is a normal condition for this valve.

7. If the dual application valve does not operate as described, overhaul or replace the dual application valve.
8. Drain the air reservoirs.
9. Remove the test gauges.
10. Start the engine.
11. Charge the air system to the air compressor governor cut-out point.
12. Stop the engine.
13. Test the brake for proper operation.
14. Remove the wheel blocks.

Air Brake Application Valve Operational Check Leakage Test

1. Block the wheels.
2. Tilt the cab. Refer to Cab Tilting in General Information.
3. Remove the upper inner fender panel. Refer to Body Front End.
4. Lower the cab. Refer to Cab Tilting in General Information.
5. Start the engine.
6. Charge the air system to the air compressor governor cut-out point.
7. Stop the engine.
8. Tilt the cab. Refer to Cab Tilting in General Information.
9. Ask an assistant to apply the brake pedal.
10. Inspect the exhaust port and the body of the dual application valve for air leakage. Air leakage of a 25.4 mm (1 in) bubble in 3 seconds is permitted.

If air leakage is excessive, overhaul or replace the dual application air valve.

11. Install the upper inner fender panel.
12. Lower the cab. Refer to Cab Tilting in General Information.
13. Test the brake for proper operation.
14. Remove the wheel blocks.