808 diff schim?

Hi, dont know if i spelled it correct but should i shim My diffs? I have taken it apart to clean it and noticed that the front pinion can be pulled 1-2mm front to back and the back 2mm or so. I bought it last summer used and drove it at the track à few times, no problem, no signs of wear what so ever but wondering if I should shims the diff and what size if thats the case. Running tekin 1700 truggy combo with 5s. Thanks

[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.

[lincpimp]

Good writeup simple.

Setting pinion depth is important, as you want as much of the pinion contactying with the ring gear as possible. Some diff setups are easier to see inside when partially assembled than others. I usually try to shim the pinion till it almost touches the diff cup, so I know the max amoiunt of the inion teeth are contacting with the ring. Then shim the ring gear as described above.

New gears will be notchy, but will wear in. You might have them smooth through most of the rotation, then they get notchy in a few teeth, that is fine, as they will wear in.