SFN-20231006C_Replace an air horn valve

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TICO Document #: SFN-20231006C (formally TES 200)

Description of Procedure: Replace a leaking plastic air horn valve

Parts Required:

  • VALVE, AIR HORN 90482 (QTY 1)

  • FITTING-ELBOW,45°1/4"TUBE PUSH-ON X 1/4" NPTM, BRASS 40881 (QTY 1)

  • SCREW, PAN HEAD, PHILLIPS, STAINLESS STEEL,#10-32 X 1 LONG 800447 (QTY 1)

  • NUT, #10-32 18-8 STAINLESS NYLOK 2 800424 (QTY 1)

  • WASHER, FLAT, SAE, #10, SS 80232 (QTY 2)

This procedure is for the replacement of a leaking plastic air horn valve (see Figure #1) located in the interior cab to the upper left of the driver’s head.

Instructions:

  1. Park the vehicle on a flat surface, and apply the parking brake and chock wheels. If your company utilizes a “Lock Out, Tag Out” policy, you should employ it during this procedure.

  2. Drain the air from the air tanks by locating and pulling on the air drain cables. These cables are located at or around the “AIR RESERVOIR DRAIN” label affixed near or on the frame rail. (See Figure #3.)

    CAUTION: Multiple drain locations could be present. Inspect the area to verify that all of the air tanks are drained of chassis air.

  1. Remove the existing plastic air horn valve from the cab wall and associated mounting hardware. Disconnect lanyard and the air lines from the “push-to-connect” fittings, taking note and marking the supply and discharge lines. (See Figures 1 & 2 above.)

  1. In the forward pre-existing mounting hole, apply some silicone sealant in the hole and install the #10-32 x 1” screw (P/N 800447) and #10 flat washer (P/N 80232). Insert hardware from the outside of the cab inward. Install the second #10 flat washer (P/N 80232) and 10-32 Nylok nut (P/N 800424) and tighten. Remove excessive sealant.

  1. Remove one of the brass fittings from the plastic valve and install it in the discharge port of the cast valve. Install the new brass fitting (P/N 40881) in the supply port of the cast valve.

  1. Install one of the removed bolts, installing from the outside in, and feed through the cast valve to the first bolt location. (See Figure 4). Rotate the cast valve counterclockwise until the cast valve comes into contact with the nut on the bolt installed with sealant.

  1. With the cast valve in this position, use the valve as a guide and VERY SLOWLY drill a 1/8” pilot hole from the inside of the cab through to the outside. Try not to chip the gel coating on the exterior surface.

  2. From the outside of the cab, slowly drill a 3/16” hole using the 1/8” diameter hole as a guide.

  1. Repeat the same process and finish drilling a 1/4” hole using the 3/16” diameter hole as the guide.

  1. With the remaining hardware from the removal of the plastic valve, secure the cast valve through the 1/4” hole that was just drilled.

  1. Reconnect the lanyard and appropriate supply and discharge airlines.

  1. Start the vehicle and inspect the lines for leaking. Pull on the lanyard to test the cast valve for operation.

  1. Remove “Lock Out, Tag Out” plaque.

  1. Return vehicle to service.