[lincpimp]

You have to shim the diff in various places to remove slop, and also create a good mesh between the two gears. I will limit this explanation to the ring and pinion gears.

On a revo, the shims used to adjust the side to side fit of the ring gear/diff cup assy are 10x12mm. The pinion is 6mm in diameter, so something like a 6x8 shim would go there.

The trick is to first shim the ring/diff cup in the housing without the pinion in there. All you are looking to do is to figure out how many shims give it a good snug fit. Place the shims between the bearing and the ring gear. When you have that done, reinstall the pinion gear and see it is too tight against the ring gear. If it is, move one shim to the cup side of the diff, between the cup and the bearing. That will move the ring gear away from the pinion, to the side, and free up the gear mesh a bit.

Heres the tricky part. You need to eyeball the pinion, and determine if it is lined up with the teeth on the ring gear. It may be sitting to far forward, and require a shim between it and the inner bearing. That would move the pinion farther into the diff case. It makes sense when you do it.

You want a good mesh, but not too tight. And when you get it right, use some good synthetic grease on the gears.