Remove the wheel, the 8 bolts that hold the axle in. If it has nuts holding the axle remove the nuts & hit the axle hard with a hammer being careful not hit the studs. Pull the axle shaft out. If it has a nut with notches in it, there will be a lock tab in one of the notches. Bend it out & screw the nut out with a hammer & punch. Remove the lock spider & screw the 2nd nut out. Than slide the hub & drum off if the brakes will alow it. If the axle has large hex nuts you will have to get a special socket to fit it. Pull the seal out of the hub. It is available at any parts store. If you need a new lock spider the are available at GM dealers. Coat the bearings with diff. grease & put some in the hub. Reassemble the parts in reverse order. Tighten the inner nut enough to remove any free play. Try it several times, this adjustment is critical. Fill the diff. completly full or a little overfull to make shure it gets back to the bearings.
