Chain/Deraillieur Jumping?

Question

Ok, to start, here are the stats. Specialized, Hardrock Pro, 26" Weinmen (spelling may be off) Disc rims with a Shimano 8spd cassette. New Shimano 8/9spd rear mtb. deraillieur and an 8 spd "Z" chain. The Problem: My chain/old deraillieur were working fine with the cassette. next thing i know, my two smallest sprockets on the cassette are jumping/skipping/grinding when I shift into them. I saw that the cassette bolt was loose, so I tightened that down. Then replaced the chain. But it was still problematic. So, I decided it must be the derailleur and went off and replaced that. But even with the two new additions, the chain, or cassestte or derailleur is stilllll jumping/grinding. I dont know if anyone else has had this problem, please help!!!

Answer 1

Sounds to me like there may one of several problems, and one problem may have caused the others...

1) The cassette cogs may not be fully engaged on the freehub body. COMPLETELY remove the cassette again and reinstall. Make sure to include the correct spacers if necessary.

2) Because the cassette was loose and you tried to ride you may have twisted a cog OR bent the derailleur hanger OR pulled the dropout out of alignment. These issues must be addressed at a shop that has the correct tools.

3) These might sound dumb, but you should check anyway... Do you have an 8 speed Shimano shifter? SRAM will NOT work. Is your derailleur Shimano Alivio or greater (Deore/LX/XT)? Most models below that are not 8 speed compatible. Do you have an 8 speed chain? SOME 7 or 9 speed models will do exactly what you explain since the links are too wide or too narrow to fit on the cogs.

EDIT: One other thing that I assume you already checked... make sure there are no stiff links in the chain!