1974 PontiacTrans Am Gears - Pontiac Tech

Since we were replacing all the old bearings, we employed a hammer and a long drift to drive the inner and outer pinion-bearing races out of the case, taking care not to let the drift slip and gouge the bearing seats.

With all the parts removed, we were off to the parts washer. Even parts that weren't going to be reused were cleaned and thoroughly inspected to determine any problems. Our old parts passed with flying colors.

After the seats for the pinion-bearing races were wiped with clean rags and solvents, we applied a light coat of silicon spray, and Bryan drove the new races into place with a brass drift.

We used a bearing press to remove the old inner pinion bearing. Why bother when we'll be installing a new bearing on the new pinion? We needed to see how many shims were behind the bearing and measure their thickness. This will be the starting point for the shim pack to set the pinion depth and our final backlash setting.

The original shims were in good enough shape to be reused after a trip through the parts washer. If they hadn't passed inspection, our Ratech kit came with new replacement shims that we could have substituted.

With the shims under it, we pressed the new inner pinion bearing into place. Bryan then mocked up the remaining parts to show the final installation order of the inner bearing, crush collar, and outer bearing. Not pictured are the new pinion seal, yoke, washer, and pinion nut that will secure the assembly.

Sans the crush collar, we installed the pinion with the shims, lightly oiled inner bearing and outer bearing, and the nut. Next, we tightened the nut in small increments to achieve the required bearing preload of 14-19 in-lb of drag. This step would normally be followed by measuring the pinion depth, but Bryan only does that when an unknown shim pack is used. When reusing an existing pinion-shim pack, he prefers to install the pinion, carrier, and ring gear, and run a pattern to determine if the depth is already correct. (Editor's Note: For a general description of how to check pinion depth, see "Maximum-Effort Fourth-Gen 10-Bolt," Oct. '06.)

We then turned our attention to the carrier and ring gear. Bryan headed back to the press to remove and install the carrier bearings on each end. We used a liberal dose of silicone spray prior to pressing on the new bearings.

Next, we removed the old ring gear, keeping in mind that on the GM 8.5-inch, 10-bolt differential, the bolts are reverse-threaded (left-hand). Bryan has seen more than one ring gear ruined by having the impact set incorrectly and stripping out threads.

Since the new ring gear is a tight fit on the carrier, Bryan put the carrier in the freezer for a few hours and then placed the ring gear in the oven at 200 degrees to heat it. The combination of hot and cold allowed the ring gear to easily drop into place. We used red Loctite on every ring-gear bolt. The bolts were then brought to the proper torque in three steps to the final torque setting of 65 ft-lb using a crisscross pattern to pull the gear down evenly against the carrier.

After prelubing all the bearings, Bryan installed the carrier with the new ring gear, carrier bearings, and races on the differential case. We reinstalled the shim amounts that were in place when we disassembled the unit between the carrier race and housing as a starting point for setting the backlash.

Bryan torqued the carrier caps to 60 ft-lb. Some instructions say snugging the caps is adequate, but he believes it's better to measure with the caps at full load.