LBS 8 vs. 9spd. derailleurs?

[keen]

"LBS 8spd./ 9spd. derailleur debate..."  
I went into my LBS today to purchase a derailleur pulley for my 9 speed XT der. The LBS mechanic noted I had a complete 8 speed drivetrain, aside from the XT Mega 9 der. He asked if my bike shifted ok? I replied- ok I guess? He stated there is a difference between 8 and 9 sp. der's. The 8 spd. pullies are 2mm wider (2mm wider cage). He showed me where there was excessive der. cage wear from the chain (wide chain ,narrow cage). I have read so many posts where many people mix and match 8/9 spd. w/ good luck & others have mixed results. Anyone notice real a difference between 8/9 spd. rear der's? I was thinking of shimming my der. cage out 2mm? Anyone attempt this? Thanx

[Simon]

Check out the files,I've posted an article on 8/9 speed compatability that should answer your questions,Simon [smiley=nod.gif]

[Gordo]

I have had some rubbing problems when running a 8 speed chain with a 9 speed deraillleurs both front and rear.

[Matno]

Definitely a problem in the front. However, I never would have imagined that the rear derailleur has chain tolerances that tight. I would think that it might cause rubbing, which you should notice when you ride (any noise drives me nuts), but how it would cause shifting problems is beyond me. As long as it's adjusted properly, it should shift fine. Many people have done this successfully (do a search on MTBR), but I can't vouch for their sensitivity to imperfection...