EXHAUST PIPE ASSY.MODIFICATION SERVICE AND PARTS UPDATE

SUBJECT: EXHAUST PIPE ASSEMBLY MODIFICATION (SERVICE AND PARTS UPDATE)

VEHICLES AFFECTED: 1991 W4 WITH AUTOMATIC TRANSMISSION

SERVICE INFORMATION:

The exhaust pipe assembly has been modified to include an Exhaust Bracket and Shims for certain NPR (W4) series vehicles manufactured as 1991 models. The modification was precipitated because the exhaust pipe flange area leading to the muffler may crack at very low vehicle mileage due to insufficient structural support. This exhaust pipe modification affects those vehicles with Automatic Transmissions ONLY. The new parts will contribute necessary support and increase durability/ reliability of the exhaust assembly.

To ensure these results, it will be necessary to modify the existing exhaust pipe assembly with these new parts.

SERVICE PROCEDURE:

The following are the procedures used to perform the Exhaust Pipe Modification. Refer to Figure 1 for parts identification.

1. Disconnect battery and chock wheels.

2. Install Exhaust Brake Bracket (1) to frame rail on pre-drilled holes and torque bolts to 17 N.m (13 ft. lbs.) (Figure 2).

3. Install Mounting Rubber (2) to Exhaust Brake Bracket (1) and torque bolt to 13 N.m (10 ft. lbs.).

4. Install the two-piece Exhaust Pipe Bracket (3) and (4) loosely, making sure the HEAT SHIELD is directly under the Mounting Rubber (2) and is facing the REAR of the vehicle.

5. Install the nut and flat washer to join the Exhaust Pipe Bracket (3) and (4) to the Mounting Rubber (2) and torque nut to 13 N.m (10 ft. lbs.).

6. Torque the Exhaust Pipe Bracket (3) and (4) bolts to 13 N.m (10 ft. lbs.).

7. Loosen the two nuts off the muffler flange studs, then install the two (2) Shims (5) to each outer side of the studs between flanges (see Figure 3). Torque nuts to 37 N.m (27 ft. lbs.).

8. Reconnect the battery and unchock the wheels.

SERVICE PARTS INFORMATION:

Kit Number Model -------- ---------- 97047012 W4 or W4-FL

The kit consists of the following components:

Part Number Description Quantity ------------ -------------------------------------- --------- 97046784 Bracket, Exhaust Pipe (with Heat Shield) 1 97046785 Bracket, Exhaust Pipe 1 97045684 Bracket, W4 and W4-FL Exhaust Brake 1 97046147 Bracket, W4-ST Exhaust Brake 1 97046148 Mounting, Rubber 1 97046036 Shim 2 94009373 Washer, Rubber Mounting 2 94009041 Nut, Rubber Mounting (2) and Exhaust Pipe 4 Bracket (2) 94008846 Bolt, Exhaust Brake Bracket (M10 X 1.25, L=30 mm) 2 94009475 Nut, Exhaust Brake Bracket 2 94009490 Bolt, Rubber Mounting (1) and Exhaust Pipe 3 Bracket (2) (M8 X 1.25, L=30 mm)

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.