AXLE SHAFT END PLAY CHECKING PROCEDURE

MODELS: 1978-1980 CABALLERO

GMC is aware that some owners have expressed concern regarding the axles on their 1978 to 1980 GMC Caballero's due to a recent media release. Should a customer request that the axle shafts on their 1978 to 1980 GMC Caballero be inspected, at the customer's expense, dealers should use the following procedure:

1. Raise the vehicle on a hoist. Mount a dial indicator on the axle housing behind either rear wheel. Rest the indicator point against the back side of the wheel or the edge of the brake drum. Refer to Figure No. 1.

2. Measure the end play of each axle shaft by grasping the tire with both hands and pushing outboard until axle shaft is felt to bottom. Zero indicator. Refer to Figure No. 1.

3. Again grasp the tire with both hands and pull inboard until axle shaft is felt to bottom. Remove hands from the tire and read the indicator. Record the indicator reading of each rear axle. Refer to Figure No. 1.

4. The readings obtained in Step No. 3 should be compared with the specifications in Chart I.

CHART I

Maximum Allowable End Play For Each Axle

Standard Limited Slip Mileage Axle Axle

0 to 25,000 .050" (1.270 mm) .080" (2.032 mm) over 25,000 .060" (1.524 mm) .100" (2.540 mm)

5. If the end play reading equals or is less than the end play specification in Chart I, Step 4, at the mileage indicated, no additional checking is required.

If the end play reading exceeds the end play specification in Chart I, at the indicated mileage, the following steps should be per- formed.

6. Remove the axle carrier inspection cover and drain the lubricant.

7. Using a screwdriver, pry between the differential pinion shaft and the end of the axle shaft to obtain maximum clearance. Refer to Figure No. 2. Insert a feeler gage between the differential pinion shaft and the end of the axle shaft to obtain a second end play reading. Record the feeler gage reading. If this reading still exceeds the end play specification in Chart I, Step 4, the axle shaft should be removed from the vehicle so the actual thickness of the axle end button can be measured.

8. Measure the axle end button thickness on the axle, using a vernier caliper. Record the vernier caliper reading. Compare this measurement to the specifications in Chart II. Refer to Figure No. 3.

CHART 11

Maximum Allowable Axle End Mileage Button Thickness

0 to 25,000 .170" (4.318 mm) over 25,000 .160" (4.064 mm)

9. If the axle end button thickness measurement obtained in Step 8 is equal to or greater than the minimum allowable axle end button thickness in Chart II, at the mileage indicated, no additional checking is required and the axle shaft should be reinstalled.

If the axle end button thickness measurement is less than the minimum allowable thickness in Chart II, at the mileage indicated, the axle shaft and the differential pinion shaft should be replaced using the procedure in the applicable service manual. For replacement, axle shaft part number 551818 and differential pinion shaft part number 22507586 should be used. To ensure that parts will be obtained as soon as possible, they should be ordered from WDDGM on a C.I.O. order with no special instruction code, but order on an advise code (2).

10. After new parts are installed, or original axle is reinstalled, verify that axle shaft end play is below the maximum allowed in Chart I. If it is not, contact your Zone Office as soon as possible.

11. Install the axle carrier cover using a new cover gasket and fill housing with the proper lubricant.

12. Lower hoist.

The following are suggested labor times for checking axle shaft end play.

a) Check axle shaft end play with a dial indicator on both axles .3 Hr.

b) Check axle shaft end play with a dial indicator and insert feeler gage and check distance between differential pinion shaft and both axle ends .4 Hr.

Until further notice, GMC is requesting that all axles and pinion shafts, which are replaced because the parts do not meet the specifications in this procedure, be retumed for Engineering evaluation. In the event a vehicle is encountered that requires the above parts, GMC will pay for the parts and labor, and in this case no charge should be made to the customer for inspection as it is included in the labor operation. The zone office should be contacted for claim authorization. Existing labor operation numbers and labor times should be used for axle shaft and pinion shaft replacement. UPS shipping charges for parts return should be included as sublet on the warranty claim. Include a copy of the repair order with the parts being returned. The repair order must contain the VIN, mileage, axle code number from the right front inboard side of the axle housing tube, and the readings obtained in Steps 3, 7 and 8 in the above procedure. Place the repair order in an envelope and attach it to the parts.

Parts are to be returned to the following address:

Metallurgical Department, GM Research ATTN: George H. Robinson GM Technical Center Warren, Michigan 48090

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.