Originally Posted by
the beef
Seven's the crappy number of indexed drivetrains. It's eight, nine, and ten speeds which are in general more intercompatible. You'll most likely need a new hub.
The old 7 spd derailleur should work fine; derailleurs generally are not too speed-specific. You'll do good to invest in a narrower chain, though - trust me.
No, you don't need a new hub, just so long as you can replace the 7-speed freehub assembly on the hub with an 8-speed unit. The part cost me $24 or so.
And I'm using the original 7-speed chain on the 8-speed system, which is correct. The only difference between a 7 and 8-speed freehub is that the 8-speed unit gives room for the smallest cog.