Actually.....
Maybe you overheard shimming, but not transmission shimming itself. Sometimes when using an aftermarket flywheel, turned down flywheel or aftermarket clutch the distance between the throwout bearing and pressure plate increases too much.
The only way to fix this is to shim the pivot ball that the fork pivots on.
http://www.youtube.com/watch?v=omAw-TgCYzM
Threaded Mode