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Hanger alignment or just bad indexing?

me-109me-109 Posts: 1,910
edited October 2015 in MTB workshop & tech
So my lad wrote off another rear mech today. SRAM X5, pulley cage separated from body.looks like it lost the retaining clip and the two came apart. I was able to replace with a new X7 and have installed with new inner and outer cables. Shifts pretty well up to 2nd, then wants to bypass it and go straight to first. Trim the indexing to get 2nd fine and then the top end gears run out and get noisy, or it tries jumping past 8th.

This was worse before I swapped the outers, I think, but I just can't get them all correct. If I line up behind the bike then it looks like the mech pulleys aren't vertical, with the lower one closer to the wheel. Might be my imagination though as it was hanging from a roof beam.

Posts

  • cooldadcooldad Posts: 32,599
    So take the hanger off and check it is straight.

    If the mech was trashed there's a good chance it isn't.
    I don't do smileys.

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  • Yes, your hanger is bent.

    Leave the hanger on, use an alignment tool to line it up with your wheel after checking your wheel is straight and fitted correctly. You cannot do it any other way. As dropouts wear, alignment drifts, especially if the dropout type is such that the wheel interface is carbon and not part of the hanger.
    A new hanger bolted on an old frame is seldom aligned well.
    New bikes out of the box are seldom aligned well.
    Buy an alignment tool, very cheap nowadays.


    Problem solved.
  • cooldadcooldad Posts: 32,599
    Really? Seriously? ^^^^^^^^^^^^^
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • me-109me-109 Posts: 1,910
    Hanger alignment it was. Too late last night to take it off and check. Just a slight tweak to straighten.
  • Yes Cooldad, really, seriously.
    You very, very rarely see a new bike out of the box with a straight hanger alignment.

    First thing for gears when building is always align the hanger.
    Some shops don't and the variability in the tune of their bikes is amazing.
  • cooldadcooldad Posts: 32,599
    You're making a bit of a mission out of something simple. We're not talking TdeF pros.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The RookieThe Rookie Posts: 27,811
    As long as the upper jockey wheel is aligned under the relevant sprocket and the chain not clipping neighbouring sockets it will work just fine, my hack bike had a very twisted mech, I twisted it back vaguely straight and it all works just fine.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • drlodgedrlodge Posts: 4,826
    As long as the upper jockey wheel is aligned under the relevant sprocket and the chain not clipping neighbouring sockets it will work just fine, my hack bike had a very twisted mech, I twisted it back vaguely straight and it all works just fine.

    If the hanger isn't aligned, the jockey wheels won't line up under the relevant sprocket properly. Becomes more sensitive on higher geared bikes (10-11 speed) and the more the rear derailleur rotates on its pivot as it moves up/down the cassette.
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  • The RookieThe Rookie Posts: 27,811
    True, but as nothing is ever exact there is a tolerance within which it will work, they may be quite tight or quite generous, but it certainly doesn't have to be within microns/seconds.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
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