[simplechamp]

Yes, you always want to check and re-shim your diffs after a rebuild. You want to shim both the pinion gear so there is no play front to back, and the ring gear so there is no play side to side. Play on either gear will allow it to "walk into" the other gear and cause binding and excess wear. Shimming the pinion gear will adjust how much area of the teeth are in contact with the ring gear. Shimming the ring gear will set the mesh between the two gears.

I'm not sure about the pinion gear, but the ring gears should use standard 13mm I.D. 16mm O.D. shims (thickness is usually 0.1-0.3mm). They will slide right over the outdrives.

Many will tell you shimming is almost an art, you just have to get the feel for it by practice. A perfect shim will be totally smooth throughout a complete rotation, but also have little to no play between the gears. For the pinion you want most of the pinion to be engaging the teeth on the ring gear, but don't go too far or the pinion will rub on the diff case. For the ring gear I usually start with a few shims on one side (pushing the ring gear towards the pinion, it will be too tight at the start), and move one shim over to the other side at a time until it feels perfect. If you are using brand new gears you want to shim a bit on the tight side (might feel a little notchy, but not too much), and the gears will wear in a bit on the first run or two (then you check them and see if any adjustment is needed). If the gears are used you can shim a tad looser.

After running for awhile you will notice a bit of play forming again in the drivetrain. At this point the gears have worn a bit, but should still have some life left, and you can re-shim them. Check to see if they are wearing evenly, something like a ring gear wearing more in one spot could indicate it's wobbling a bit. Eventually the gears will be worn past the point of shimming, and you can replace them.