Differential Install: Small Details Make a Big Difference (Part 1)

Taking care of the details requires knowing which details are important, and having the discipline to check every detail on every job. Here is a partial list of details that we have found to make a difference when assembling a differential.

Pay very close attention to the bearing hubs on the carrier case. If the old carrier bearing spins on the case, the new bearing will not fit tight and will also spin. Any wear due to a spinning carrier bearing will cause the backlash to open up and the ring & pinion gears will eventually break.

Look carefully at the side gear bores and thrust washer surfaces to make certain they are not worn or galled. Make sure the cross pin shaft bores fit the cross pin tightly.

Check the ring gear flange with a dial indicator to make sure there is minimal or no run-out.

There are a lot of opinions as to how much carrier run-out is acceptable. We have seen as little as 0.005″ cause problems and we have seen differentials work fine with 0.009″ or more. The main thing that we look at is backlash variation. Keep the backlash variation under 0.005″ if possible. In a perfect world no variation would be the goal. However, even with a straight case the backlash can vary 0.005″ without any negative consequences, so this is an area where each assembler will have to decide how much they are willing to allow.

Also look closely at the spider gears and cross pin shaft. The spider pinion gear and side gear teeth should be without pits or chips, and should not show any signs of heavy wear at the base of the contact patch. The spider pinion gears should not have any heavy wear or galling on the inside where they contact the cross shaft, and the cross pin shaft should show no more than light; even wear on the surface that contacts spider pinion gear without scratches or galling.

The pinion yoke is another part that can cause a lot of problems if it is not in good shape. It is good idea to inspect the ears or shoulders that retain the universal joint. If there is any wear in these areas it is best to replace the yoke. Also inspect the seal surface closely. Small grooves or light rust can sometimes be polished away, but any irregular spots can cause the seal to leak if they do not polish out completely. Repair “redi sleeves” are available to press on the yoke and replace the seal surface of my popular models. These sleeves work fair in most cases but usually do not hold up as long as a new yoke

The most often overlooked problem that we have found with yokes is the splines. On some models the splines seem to last forever, and on some they loosen up quickly. The splines should always fit tight and it should take a lot of pressure or pounding to drive the yoke down until it seats against the outer pinion bearing. One other area to inspect on the yoke is the surface that touches the outer pinion bearing or slinger. If this surface has light wear it can be filed down flat with a hand file as long as the surface is kept true and is not filed unevenly.

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