Upgrades, upgrades, upgrades...

[Megazone23]

Okay, got a quick question regarding shimming the diff. If I understand things clearly (which is likely suspect at this time), there is a shim inside the diff cup with the spider gears (Traxxas Part 3981). But in another thread re: rebuilding the diff, someone said it may be necessary to shim the diff assembly within the diff case as well, but I don't see any shims indicated in the Traxxas exploded diagram, so what size (inside and outside diam) shims should I get, and will it interfere with the bearings?