Operational Test
- Apply the parking brake.
- Block the wheels.
Remove the differential lock relay valve. Refer to
Differential Lock Relay Valve Replacement.
- Install an air pressure gage in a common control and supply air line connected to the control and supply ports of the differential lock relay valve.
- Install an air pressure gage into the delivery port of the differential lock relay valve.
- Gradually apply air pressure to the common control and supply line. As the pressure increases, observe the two air pressure gages.
| 5.1. | Note the common control and supply line air pressure gage when air pressure is delivered to the delivery port. |
| 5.2. | The common control and supply line inlet pressure should be at 290 kPa (42 psi) when air pressure is provided to the delivery port of the differential lock relay valve. |
| 5.3. | If the test does not result in the above conditions, repair or replace the differential lock relay valve. |
- Slowly reduce the common control and supply line inlet air pressure. As the pressure decreases, observe the two air pressure gages.
| 6.1. | Note the common control and supply line air pressure gage when air pressure from the delivery port is exhausted from the exhaust port. |
| 6.2. | The common control and supply line inlet pressure should be at 193 kPa (28 psi) when air pressure is vented through the exhaust port. |
| 6.3. | If the test does not result in the above conditions, repair or replace the differential lock relay valve. |
- Remove the air pressure gage from the delivery port of the differential lock relay valve.
- Remove the air pressure gage in a common control and supply air line connected to the control and supply ports of the differential lock relay valve.
- Install the differential lock relay valve. Refer to
Differential Lock Relay Valve Replacement.
Air Leakage Test
- Apply the parking brake.
- Block the wheels.
- Start the engine. Charge the air system to the air compressor governor cutout point.
- Stop the engine.
- Switch the differential lock control valve lever to the ON position.
- Inspect the supply, control and delivery ports for air leaks using a soap solution. Air leakage is not allowed. If any leaks are present, repair or replace the differential lock relay valve.
- Inspect the exhaust port for air leaks using a soap solution. A slight bubble leakage is allowed. If air leakage is excessive, repair or replace the differential lock relay valve.
- Drain all of the air reservoirs. Refer to
Air Brake Reservoir Draining.
- Remove the supply and control air lines from the differential lock relay valve. Refer to Air Brakes.
- Install an auxiliary common air supply and control line into the differential lock relay valve.
- Remove the delivery port air line from the differential lock relay valve.
- Install a plug into the delivery port of the differential lock relay valve.
- Apply 69 kPa (10 psi) of air pressure to the auxiliary common air supply and control line.
- Inspect the exhaust port for air leakage. Air leakage less than a 25.4 mm (1.0 in) bubble in 5 seconds is acceptable.
- If the air leakage is too much, repair or replace the differential lock relay valve.
- Remove the air pressure from the auxiliary common air supply and control line.
- Remove the plug from the delivery port of the differential lock relay valve.
- Install the delivery port air line into the differential lock relay valve.
- Install the supply and control air lines into the differential lock relay valve.
- Start the engine. Charge the system to the air compressor governor cutout point.
- Stop the engine.
- Inspect for air leaks using a soap solution.
- Remove the wheel blocks.
