Originally Posted by
jpaschall
These questions seem to cropping up quite a bit lately, so I'll jump on the bandwagon. I've got a Deore MT-62 RD and I'm wondering if I can use it to shift 8-speeds with the Shimano 8-speed bar ends. The RD is technically designed for 7-speed, but Velobase says it will shift 8 fine. Is that all I need to know? No problems here?
For the most part, there is no difference between a 7/8/9/10 speed Shimano derailleur. That's not true with really early generation Dura-Ace stuff, and some other exceptions, but its a known quantity in the cyclocross scene where they mix/match kit commonly across "speeds."
Shimano and Campagnolo - Can't We All Get Along? - Cyclocross Magazine - Cyclocross News, Races, Bikes, Photos, Videos
From that piece:
Does it matter what Shimano rear derailleur you use? Not really. There’s no such thing as a Shimano 7, 8, 9, or 10-speed rear derailleur. As long as you avoid pre-9-speed Dura Ace rear derailleurs, everything will work great.