Derailleur Question-
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  1. #1
    mtbr member
    Reputation: Ultimate G's Avatar
    Join Date
    Jul 2004

    Derailleur Question


    I need to replace my rear derailleur. I am trying to learn how to pick out the best replacement.

    I have a 2002 Shimano XT 8 speed.

    1. What do I need to know when I'm picking out a new derailleur?
    2. Is it important to get another 8 speed, or will a 9 speed fit, too?
    3. Any problems using a Deore or SLX? Are all models of SLX the compatable, or are there other variables I need to match up?
    4. The old derailleur was 85mm between cogs - how do I verify this measurement when ordering a new derailleur?


  2. #2
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
    Join Date
    Nov 2007
    1. Brand, cage length, top-normal vs. low-normal, 10-speed vs. not 10-speed, Shadow vs. not Shadow.
    2. A 9-speed is fine. A 10-speed is not fine. It has to be Shimano.
    3. Nope. They're lower component groups than XT, but work fine. Not all models of SLX will be compatible - avoid 10-speed. My bike gets Deore until I stop breaking them before I wear them out.
    4. Dunno. I've never seen it given as a measurement. However, Shimano MTB derailleurs do come in two cage lengths. SGS is "long cage" and most triple crank drivetrains will require it. GS is "medium cage," sometimes confusingly referred to as "short cage," and double and single ring drivetrains can use it and should perform a little better.

    Most derailleurs are high-normal. These shift to a more difficult gear when you click the little tension release button. I'd replace my derailleur with another of the same, unless I had a reason to try the other kind. There's some acrimony about Shadow vs. non-Shadow. I have a Shadow on my MTB and non-Shadow on my 'cross bike. (Previous MTB derailleur was also non-Shadow.) I think the Shadow derailleur is cool. The housing doesn't have nearly as much of a bend before it reaches the stop on the derailleur, and I think spring tension is higher. Shimano claims the Shadow model is also lower profile, and you're less likely to tear it off while riding. I don't know if it really makes a difference. I do think there's a little difference in the angle of the linkage, such that someone who needed to use the B-screw to get their old non-Shadow derailleur to clear the largest cogs, especially if it's a 36t or something, won't need it as much anymore. This is part of why my 'cross bike got non-Shadow - long-term plans for that drivetrain include going back to a road cassette.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

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