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  1. #1
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    Derailleur/Crankset compatability

    Has anyone tried running a 3x front derailleur on a 2x crankset(XTM785)?

    I had a post a while back where I was having shifting issues with the 785 crank(2x). I have an XT 3x front derailleur that I was wanting to try on this setup and was hoping it might work.

    The reason for this is that I am not happy at all with how my bike shifts. I originally had SLX shifters(3x only) a non series M552 3x crank(large ring removed and replaced with a bash), XT 3x front derailleur(limit screws adjusted to not shift past mid ring) and a set of Middleburn rings(26/36). This setup shifted flawlessly.

    Well, in my infinite wisdom I decided to upgrade(so I thought) to a set of XTR shifters, XTR 2x front derailleur and a new XT M785 2x crankset. I reinstalled the 26/36 rings and a Blackspire 2x specific defender bash ring. I never could get this to shift up to the big ring without skipping. When I set the clearance on the front derailleur to Shimano specs, it would hit the bashring when shifting to the large ring. I called Blackspire and was told I need to raise the derailleur to just barely clear the bash ring. I did this and it would shift but it skipped quite a bit. I then removed the bash ring and readjusted the derailleur back to Shimano specs and it really did not shift any better than it did with the bash ring installed.
    I was told by the LBS that the aftermarket rings would not shift as well as the Shimano rings due the them not having as good of a ramp profile or the number of pins the Shimano rings have(funny that they shifted great on the 3x crank before though).
    I have now replaced the aftermarket rings with the Shimano rings that came with the crank(26/38). They don't shift ANY better than the aftermarket rings did. In order to get it to shift with any reliability, I have to let the outer limit set so that the derailleur will actually over shift a little. This means I have to really mash on the shifter and let it completely shift before I let off of the lever.

    I'm thinking if I replace the front derailleur with a 3x that's made to have a little more clearance over the chain rings, it might allow it to shift like before and hopefully I can still retain the bash ring. I really want to go back to a 36 tooth ring instead of the 38.

    This is getting very frustrating. I know this thing SHOULD shift properly.

    I've even had it to the bike shop several times and they haven't had any better luck than I had. If it matters, this is on a Santa Cruz Tallboy Lt.

    thanks
    Dave

  2. #2
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    Mostly the difference between 2x and 3x FDs is tooth capacity. What exactly is the problem you are having?

  3. #3
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    Quote Originally Posted by jlmuncie View Post
    Mostly the difference between 2x and 3x FDs is tooth capacity. What exactly is the problem you are having?
    I cannot get my bike to shift properly from the small ring to the big ring with the 2x derailleur. Everything is now set up for 2x(shifter, derailleur and crank set). If I raise my 2x derailleur up enough the clear the bash guard(its the new defender which mounts to the outside of the 785 crank), it won't shift properly. When everything was originally set up as a 3x (3x shifter, 3x derailleur and 3x crank with a 26/36/bash) it shifted great. I've read that the 3x derailleurs were built so they would shift properly while having greater clearance over the chain rings(I guess because they were designed to originally clear the outer 42 tooth factory ring on a 3x) If so, that would allow me to move the derailleur up to clear the bash ring while still allowing it to shift.

    I just didn't know if the throw on the derailleur would be the same. I've heard of people using 2x derailleurs with a 3x shifter but never the other way around.

    Dave

  4. #4
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    Is it only hard to shift when on the larger cogs in back? What kind of BB do you have? Is there any possibility that you shifted the chain line out slightly when you changed cranks? Are you soft-pedaling when you shift?

  5. #5
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    Quote Originally Posted by jlmuncie View Post
    Is it only hard to shift when on the larger cogs in back? What kind of BB do you have? Is there any possibility that you shifted the chain line out slightly when you changed cranks? Are you soft-pedaling when you shift?
    Actually, whats weird is that it seems to shift a little better while in the bigger cogs. It's an XT external bottom bracket. I have a 73mm so I have one shim on the drive side(identical to how it came from the factory). I am peddling at a steady cadence when I try to shift. No different than when I had it set up as a 3x. I know if I have any strain on the pedals(like going slightly uphill) while shifting, it won't hardly shift at all. With the old setup, it didn't matter how I was peddling, it shifted nearly instantly.

    Does the 3x derailleur have the same "throw" as the 2x? I know the detents are in the shifter and not the derailleur but I don't know if one click on the shifter will move a 3x more or less than one click with a 2x. I may have to just give it a try this weekend if I get the chance. What gets me is that the LBS hasn't been able to get it right either.

    Dave

  6. #6
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    Is your XTR 2x FD a 9sp or 10sp? The 9sp ones were designed for a cable pull of 11mm, and the 10sp ones for a cable pull of 7mm. Shimano shifters (whether 9sp or 10sp) pull 11mm on the first shift and 7mm on the second. So, if you're using a 9sp double FD and have it set up on the second shift (which the mode selector on the newer 10sp shifters forces you to do when in 2x mode), it will not move far enough and will cause the problems you are describing.

  7. #7
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    Quote Originally Posted by PerthMTB View Post
    Is your XTR 2x FD a 9sp or 10sp? The 9sp ones were designed for a cable pull of 11mm, and the 10sp ones for a cable pull of 7mm. Shimano shifters (whether 9sp or 10sp) pull 11mm on the first shift and 7mm on the second. So, if you're using a 9sp double FD and have it set up on the second shift (which the mode selector on the newer 10sp shifters forces you to do when in 2x mode), it will not move far enough and will cause the problems you are describing.
    Yeah, I forgot to mention that mine is a 10 speed(Dynasys). Gonna try the 3x derailleur this weekend and see if it clears up the problem.

    Thanks for the reply.
    Dave

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