Air Brake Inspection and Leak Test

sd mm 42.09.001

Important: If any of the tests in the following procedure fail, refer to  of the 108SD and 114SD Workshop Manual to test individual air brake components and valves.

    Warning: Some steps in this operation require the parking brakes to be released. Make sure the vehicle is on a level surface and all tires are chocked. Failure to do so could result in the vehicle rolling, causing personal injury and/or vehicle damage.

  1. With the vehicle parked on a level surface, shut down the engine, apply the parking brakes, and chock all tires.
  2. Completely drain all air reservoirs.
  3. Install accurate test gauges in the primary and secondary reservoirs.
  4. Start the engine and run it at a fast idle.
  5. Record reservoir pressures when the low-pressure warning turns off.
  6. Record governor cut-out pressure and air dryer purge pressure.
  7. Reduce service air pressure by applying and releasing the service brakes several times, and record governor cut-in pressure.
  8. Charge the air system to governor cut-out, shut down the engine, and apply the parking brakes.
  9. Allow pressure to stabilize for one minute.
  10. Observe the installed service reservoir gauges. The pressure should not drop more than 10 psi (69 kPa) within five minutes.
  11. If necessary, start the engine and charge the air system. Shut down the engine and release the parking brakes.
  12. Make and hold a full service brake application, allowing the pressure to stabilize for one minute. Observe the installed service reservoir gauges. The pressure should not drop more than 15 psi (103 kPa) in five minutes.
  13. With the air system at full pressure and the engine idling, perform the following:

    • On trucks, operate the parking brake control valve and note that the parking brakes apply and release promptly as the control valve knob is pulled out and pushed in on the spring brake axles only.

    • On tractors, operate the trailer supply control valve knob. Note the air coming out of the trailer control coupling. Operate the park control knob and note that the parking brakes apply and release promptly as the knob is pulled out and pushed in. Block the trailer supply coupling, and push the trailer supply control valve and park control valve knobs in. When the park control valve knob is pulled out, the trailer supply knob should also come out.

  14. Build air system pressure to cut-out and shut down the engine.
  15. Completely drain the secondary (front axle) reservoir. On vehicles equipped with a Dryer Reservoir Module (DRM) or AD-IS with the air dryer attached to the reservoir, the primary (rear axle) reservoir pressure should not drop below 65 psi (448 kPa). On vehicles equipped with single check valves, where the air dryer is not attached to the reservoir, the primary reservoir should not lose pressure.
  16. Make a service brake application. The rear axle brakes should apply and release and the brake lights should illuminate.

    On tractors, with the trailer supply knob pushed in, the trailer control coupling should deliver air during the brake application.

  17. Push the trailer air supply valve knob in. With the secondary reservoir still completely drained, slowly drain the primary reservoir and record the pressure at which the knob automatically comes out. This pressure should be 20 to 45 psi (138 to 310 kPa).
  18. Close the drain cocks, recharge the system, and completely drain the primary reservoir. On vehicles equipped with a DRM or AD-IS with the air dryer attached to the reservoir, the secondary reservoir pressure should not drop below 65 psi (448 kPa). On vehicles equipped with single check valves, where the air dryer is not attached to the reservoir, the secondary reservoir should not lose air pressure.
  19. On tractors only:
    1. Start the engine and build the system air pressure to governor cut-out.
    2. Shut down the engine and leave the parking brakes released.
    3. Completely drain the primary reservoir.
    4. Make a modulated service brake application by depressing the brake pedal. The front brakes should apply and release and the brake lights should illuminate. In addition to the front brakes, with the trailer supply knob pushed in, the trailer control coupling should deliver air during the brake application.
  20. On trucks only:
    1. Start the engine and charge the air system until governor cut-out.
    2. Shut down the engine and leave the parking brakes released.
    3. Completely drain the primary reservoir.
    4. Make a modulated service brake application. Both front and rear brakes should modulate. At a steady full brake application, the pressure should not drop more than 10 psi (69 kPa) within five minutes.
  21. Drain all reservoirs and remove the gauges from the service reservoirs. Close the reservoir drain cocks.
  22. Remove the chocks from the tires.
Note:
Parent topic: Brakes
Document Number: 0000120463
Manual Publication Date: 2024-05-23
Topic Publication Date: 2024-10-30