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  1. #1
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    Front Derailleur Chain Rub

    Hey,

    I have a 2x10 SRAM X9 setup and have recently installed a BBMount chain guide for a 2x10 setup and everything was good and silent until the bike was taken for a test ride.

    I don't use the 'granny ring' often but there seems to be considerable rub when applying non-driveside pressure when pedaling.

    I have tried maxing out the limit screws in the appropriate directions to the point where shifting is no longer efficient; making any further adjustment pointless.

    Is it fair to assume that the extra few millimeters that the guide has added to the chain line has caused an irreversible (and not longer adjustable) chain line spacing? Or could slight twisting of the chain be causing this?

    Am I missing something that may solve the issue?

  2. #2
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    Sounds like a cable tension issue. What gear combination(s) are you in when it rubs? Is it rubbing on the inboard or outboard side of the FD?

  3. #3
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    Cheers for replying,

    Its rubbing inboard when on the granny ring at the front and the lowest (largest sprockets) at the rear.

    Which seems strange as this is when the chainline is at its most direct.

    There is no rub whatsoever when running on the outer chainring and shifting is 100% across the drivetrain.

  4. #4
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    It does sound like the extra bit you moved the crack outboard has resulted in cable tension holding the FD out. Try starting from scratch using the instructions below.

    Park Tool Co. ParkTool Blog Front Derailleur Adjustments

  5. #5
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    Most setups have you remove a spacer when you add a BB mounted chain guide - did you?
    You can try swinging the rear of the front derailleur a tiny bit to align it better with the chainline. It won't be exactly parallel to the front chain ring but will still work OK.

  6. #6
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    It does sound like it's just a matter of adjusting the front derailleur, but what crank do you have on the bike?

  7. #7
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    Thanks for the responses.

    When out on the last ride; when on the low gears on the cassette and granny on the front; shifting to the outer ring struggles. The chain skips on the way up.
    I adjusted limit screw to help push the chain up, to get it far enough to shift causes the chain to fall off crankside when on higher cassette gears.


    I have setting up the derailleur from scratch last night but with little success. The chain will now shift from granny ring to outer ring but only when on the middle of the cassette, the lower gears cause the chain to struggle to shift and with the high gears; the same as before. The chain will jump down to the crankarm.

    Any advice?

    I have read many articles on adjustment and I have tried low and high tension routing, but the derailleur cant seem to push the chain far enough on the initial shift to get it up onto the outer ring.

    To sbchisholm I am running SRAM X9 39 - 26tooth.

    To Slash5 There was a spacer there 3/4mm which I removed and replaced with the 2mm which came with the chainguide to maintain chainline.

    Any help appreciated; I am considering getting rid of the derailleur as I rarely use the granny-ring; but as it is there I would like it to function. Its a bit anal I know but the bike has to be mechanically sound and I would like to have the confidence that my chain isn't going to jam up when out.

  8. #8
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    Your high limit on the FD is not adjusted correctly. You will need to turn it back in to keep the chain from overshifting onto the crankarm.

    Most setups will struggle if you try to shift from a small chainring to a larger one while on your largest cog in back. In this case though it does sound like you shifted the chainline out a little. Have you tried removing the BB spacer? Usually a BB mount guide will replace the existing spacer completely so you shouldn't need one.

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