Another common problem is a bent clutch disc, if alignment pins weren't used during the last installation, it's easy for the installer to become fatigued and allow the transmission to hang from the pilot shaft, bending the plate. Alignment pins are easy to make. Just cut the heads off the proper size bolts and cut a slot in the ends to allow installation and removal with a large screwdriver. They support the transmission in alignment and make the whole job easier. Here's a shot taken that last time I did a clutch install:
[IMG]http://img28.imageshack.us/img28/7816/bellhousingbolts.jpg[/IMG]Worn out motor mounts can also cause clutch chatter, by allowing the engine to flop around during engagement.
