CAMPAIGN: REAR AXLE WHEEL BEARING SEIZURE

Models: 1991 W7R042 GMC Forward

General Motors of Canada has determined that certain 1991 W7R042 GMC Forward vehicles have defective rear axle wheel bearings. These wheel bearings have improperly machined inner races which can cause excessive friction under some operating loads, resulting in seizure of either the inner or outer bearing at very low mileage. This bearing seizure can cause noise, possible rear wheel lockup, or possible rear wheel separation. If lockup or separation occurs while the vehicle is in motion, a vehicle crash could occur without prior warning.

To correct this condition, dealers will replace the inner and outer bearings and oil seals on both sides of the rear axle.

VEHICLES INVOLVED

Involved are 21 1991 W7R042 GMC Forward vehicles listed below:

J8DM7A1U1M3200144 J8DM7A1NXM3200478 J8DM7A1N1M3200630 J8DM7A1U1M3200151 J8DM7A1N8M3200494 J8DM7A1U5M3200654 J8DM7A1U4M3200211 J8DM7A1N1M3200496 J8DM7A1UOM3200657 J8DM7A1U9M3200379 J8DM7A1U4M3200497 J8DM7A1U2M3200661 J8DM7A1U4M3200385 J8DM7A1U9M3200513 J8DM7A1U6M3200663 J8DM7A1U6M3200405 J8DM7A1NXM3200531 J8DM7A1U3M3200667 J8DM7A1U7M3200459 J8DM7A1U3M3200572 J8DM7A1NXM3200674

All affected vehicles have been identified by the VIN listing provided to involved dealers with this bulletin. Any dealer not receiving a listing was not shipped any of the affected vehicles.

DEALER CAMPAIGN RESPONSIBILITY:

Dealers are to perform this campaign on all involved vehicles at no charge to owners, regardless of kilometres traveled, age of vehicle, or ownership, from this time forward.

Whenever a vehicle subject to this campaign is taken into your new or used vehicle inventory, or it is in your dealership for service, you are to ensure the campaign correction has been made before selling or releasing the vehicle.

Owners of vehicles recently sold from your new vehicle inventory are to be contacted by the dealer, and arrangements made to make the required modification according to instructions contained in this bulletin.

CAMPAIGN PROCEDURE:

Refer to Section 4 of the Service Policies and Procedures Manual for the detailed procedure on handling Product Campaigns. Dealers are requested to complete the campaign on all transfers as soon as possible.

OWNER NOTIFICATION:

All owners of record at the time of campaign release are shown on the attached computer listing and have been notified by first class mail from General Motors. The listings provided are for campaign activity only and should not be used for any other purpose.

PARTS INFORMATION:

Parts required to complete this campaign should be ordered through regular channels, as follows:

Part Number Description Quantity/Vehicle ----------- ------------------- ---------------- 94036686 Seal, Hub Timer Oil 2 94036690 Seal, Hub Outer Oil 2 94057671 Bearing, Hub Inner 2 94057672 Bearing, Hub Outer 2

PARTS AND LABOUR CLAIM INFORMATION:

Credit for the campaign work performed will be paid upon receipt of a properly completed campaign claim card or DCS transmission in accordance with the following:

Repair Code Description Time Allowance ---------- ------------------------------------- -------------- 2A Replace both left and right inner/outer bearings 4.5 and inner/outer oil seals

Time allowance includes 0.1 hour for dealer administrative detail associated with this campaign. Parts credit will be based on dealer net plus 30% to cover parts handling.

SERVICE PROCEDURE:

CAUTION:

If any wheel experiences damage to a single stud caused by a loose-running wheel, all studs should be replaced. A loose-running wheel may cause only one stud to break, but the other studs could be internally fatigued to the point of being damaged. Replacing only the broken stud and remounting the wheel may cause further damage and personal injury. If the stud holes in the wheels have become larger in size or distorted, replace the wheel.

REQUIRED TOOLS & EQUIPMENT

98.4 mm (3.875 inch) Hex Bearing Nut Wrench J-487 1, Three-Leg Bar Type Puller J-34577, Rear Wheel Hub Puller Pilot J-34913, Tension Scale Wheel Dolly Standard Screwdriver Solvent & Brush Mild Steel Drift

REMOVAL (Refer to Figure 2)

1. Raise the rear axle and place jack stand under the frame. Vehicle wheels must be off the floor. 2. Remove wheels from the hub (74) using a wheel dolly (see Figure 3). 3. Remove axle shaft (82). 4. Remove outer oil seal (81) from the hub (74). 5. Remove bolt (80) and washer (79), then nut (78) (use wrench in Figure 4) and outer bearing (77). 6 Remove hub (74) using JA871 and J-34577 (see Figure 5). 7. Remove ring (69) from the hub (74), and use a screwdriver to remove seal (70). 8. Remove inner seal (70) and inner bearing (7 1) from the hub (74). 9. Remove bearing cup (outer ring) from the hub (74) using a drift 10. Clean axle housing end (65) and hub (74) using a solvent and brush.

INSTALLATION OF NEW REAR WHEEL INNER/OUTER BEARINGS (REFER TO FIGURE 2) ----------------------------------------------------------------------- 1. Install new bearing cups (outer rings) using a mild steel drift to drive them in. 2. Pack the new inner bearing (71) with NLGI No. 2 or 3 multi-purpose type grease or equivalent and install in the hub (74). 3. Install new inner seal (70) with the lip outward and snap ring (69) into the hub (74). 4. Fill the hub (74) with a 990g (2.18 lbs.) grease NLGI. No. 2 or 3 multi-purpose type or equivalent and install. 5. Pack the new outer bearing (77) with grease NLGI No. 2 or 3 multi-purpose type or equivalent and install 6. Initially install nut (78) to zero torque so hub (74) spins freely, then tighten nut (78) using J-34913 to obtain bearing preload specification of 67 N (15 lbs) (see Figure 6). 7. Install new outer oil seal (81) with the lip outward and slip in axle shaft (82).

8. Install wheels on the hub (74), using a wheel dolly: make sure to tighten stud nuts finger tight first, then torque stud nuts to 465 N.m (345 ft lbs.) in sequence as in Figure 7. 9. Remove the jack stands and lower the vehicle. 10. Install "Campaign Identification Label."

INSTALLATION OF CAMPAIGN IDENTIFICATION LABEL

Clean surface of radiator upper mounting panel and apply a Campaign Identification Label. Make sure the correct campaign number is inserted on the label. This will indicate that the campaign has been completed.

Dear General Motors Customer.

General Motors of Canada has determined that certain 1991 W7 GMC Forward vehicles have defective rear axle wheel bearings. These wheel bearings have improperly machined inner races which can cause excessive friction under some operating loads, resulting in seizure of either the inner or outer bearing at very low mileage. This bearing seizure can cause noise, possible rear wheel lockup, or possible rear wheel separation. If lockup or separation occurs while the vehicle is in motion, a vehicle crash could occur without prior warning.

To correct this condition, dealers will replace the inner and outer bearings and oil seals on both sides of the rear axle.

This service will be completed for you at no charge.

Please contact your GM dealer as soon as possible to arrange a service date. This letter identifies your vehicle. Presentation of this letter to your dealer will assist their Service personnel in completing the necessary correction to your vehicle in the shortest possible time.

Further assistance, if required, may be obtained from our Customer Assistance Centre, toll free, by calling 1-800-263-3777, or if you live in Quebec, 1-800-263-7854.

We are sorry to cause you this inconvenience; however, we have taken this action in the interest of your continued satisfaction with our products.

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.