Originally posted by boudreaux If they are the 7 or 8 speed,they interchange. 9 speed are thinner and are lager in diameter due to more teeth. If both mechs are 9 speed, no problem.
I've been running a 9sp XT rear derailleur and LX 9sp cassettes/hubs on my MTB for about 4 years with NO problem. I ran an XT for a while but one of the dinky cassette "arms" broke under load so went back to LX for the price and durability.
I've also used second-hand lx jockey wheels in the XT with no prob.