Rear Air Brake Relay Valve Operational Check Operational Check

1. Block the wheels.
2. Start the engine.
3. Charge the air supply to the air compressor governor cut-out point.
4. Stop the engine.
5. While you check each wheel, ask an assistant to apply the brakes hard and then release the brakes several times.

•	Ensure that the brakes apply and release promptly at each wheel.

•	If the brakes do not apply and release promptly, overhaul or replace the relay valve.

6. Remove the wheel blocks.

Rear Air Brake Relay Valve Operational Check Leakage Test

1. Block the wheels.
2. Start the engine.
3. Charge the air system to the air compressor governor cut-out point.
4. Stop the engine.
5. Release the brake pedal.



6. Inspect the exhaust port and the area around the exhaust port retaining ring for air leakage. Air leakage less than a 25.4 mm (1 in) bubble in 3 seconds is acceptable.

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

7. Ask an assistant to apply the brake pedal firmly.
8. Inspect the exhaust port for air leakage. Air leakage less than a 25.4 mm (1 in) bubble in 3 seconds is acceptable.

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

9. Inspect the outside of the valve where the cover joins the valve body for air leakage. Air leakage is not pemissable.

If any bubbles appear, overhaul or replace the relay valve.

10. Remove the wheel blocks.