• This topic has 7 replies, 5 voices, and was last updated 5 years ago by Yak.
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  • Rear mech woes
  • Bez
    Full Member

    I seem to have a rear shifting problem which, despite nearly 30 years of pretty painless fettling of derailleur drivetrains, I’m struggling to solve.

    The frame is a Cube Attention SL 2017 and the build is new. Drivetrain is 9 speed. I’ve had a go with two mechs (first a brand new long-cage M370 Alivio, then an old medium-cage M750 XT) and two cassettes (first a Sunrace 11-36, then a Shimano 11-32). According to the spec sheet, the full bike was specced with a 10sp drivetrain using an M781 XT Shadow Direct Mount mech and a Shimano 11-36 cassette. I’ve tried setting this up both as a (slightly makeshift) 1x drivetrain and as a 2x. Finally, it’s worth noting that my knowledge of MTB kit mostly dates from 10-30 years ago, so I may be ignorant to some nuances of modern mechs.

    First problem is this: neither mech will reach the lowest gear (largest sprocket). Looking from the rear of the bike, the mech hanger appears to sit around 1cm outboard of the dropout where the QR nut sits. This is unlike my other bikes where the mech is at most a couple of mm outboard of the dropout face. To illustrate the point, the M750 was taken from one of my (fully functional bikes) and before I adjusted the stops it lined up with third gear, ie the position of the hanger on this bike is further outboard by two gears’ worth of distance. Which would be fine, but even if I back out the stop screw as far as possible, neither mech will quite reach first gear.

    So: either the mech mounting point needs to come back inboard, or modern mechs are designed to operate over a different range and I need to find a suitable mech.

    Then there’s the other problem, which is that the upper jockey wheel sits very close to the sprockets. In the four lowest gears of the 36 cassette it’s enough to cause a lot of rumbling and even some skipping of the chain; with the 32 cassette it’s a little better, but the M370 mech is still pretty flaky and while the M750 is just about tolerable in second gear, if I could get it to reach first it would still have issues.

    So: the mech mounting point appears to be either too far rearward, too high, or both; or modern mechs are designed to operate over a different range of mounting positions and I need to find a suitable mech.

    If I wasn’t out of date with MTB kit I’d say the mech hanger was bollocks (it’s not damaged: it’s clearly straight) and I’d see if I could find a generic one to replace it. But maybe derailleurs have moved on enough that they’ve required different frame designs, even for basic XS frames with QR axles…?

    Either way it seems I need to buy more kit, which is annoying (especially after having to buy a second set of brakes when the frame wouldn’t take BB7s) so I figured I’d best check whether I’m missing anything simple before trying something else…

    Should I look for a new hanger? A(nother) new mech? Or go proper 1x with a radically different mech and cassette?

    bigyan
    Free Member

    You need a stanard mech hanger, or a direct mount mech (some mechs you can remove the link on to make them direct mount

    benpinnick
    Full Member

    Probably a direct mount mech hanger, meaning you can only run Shadow mechs and you’ll either need a DM mech or remove the B link from yours.

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    scotroutes
    Full Member

    the full bike was specced with a 10sp drivetrain using an M781 XT Shadow Direct Mount mech

    I suspect this is your problem

    Yak
    Full Member

    You need a 9speed shimano direct mount mech with the b-link removed.

    Unfortunately it is neither of the mechs you have. You need something like an m4000 mech.

    Bez
    Full Member

    Right you are then, that seems a pretty firm answer 🙂 Thanks.

    *shakes piggy bank*

    Bez
    Full Member

    Thanks all. The Halfords near work had an M4000 which set me back £23 after Cycling UK discount, so I fitted it this evening (after nearly losing the spring and bushing that I wasn’t expecting to fly off when I unbolted the B Link) and hey presto, it’s running fine. Much appreciated.

    Yak
    Full Member

    Good to hear you are sorted.

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