For 1990-2009 cars only
- Block the wheels.
- Test the dual air pressure gauge with two test gauges.
- Install the two test air pressure gauges in the delivery lines from the valve. Install one in the primary circuit for the rear brakes and one in the secondary circuit for the front brakes.
- Start the engine.
- Charge the air system to the governor cut-out point.
- With the brake pedal released, verify that both test gauges read zero air pressure.
- Replace the application valve (4) if the gauge does not read zero.
- Apply the brake pedal.
- Check that the test air pressure gauges show the same approximate pressure as the dual air pressure gauge. The front brake pressure is normally 14-28 kPa (2-4 psi) lower than the rear brakes.
- If the pressure is too low.
- Replace the valve. Refer to Air Brake Application Valve Replacement .
- Release the foot brake.
- Check that the test gauges promptly drop to zero.
- If the gauges do not drop to zero, check the application valve (4) for sticking or a sluggish response.
- Replace the valve (4). Refer to Air Brake Application Valve Replacement .
- Move the brake pedal to several positions.
- Check that the test gauges show varying air pressures consistent with the pedal position.
- Turn off the engine.
- Drain the air system reservoirs. Refer to Draining Reservoirs .
- Remove the test gauges.
- Check the brake operation.
- Reconnect the line.
- Remove the wheel blocks.
