Gears jumping after rear derailleur knock - why?

Discussion in 'Cycling Equipment' started by docsuperb, Apr 28, 2011.

  1. docsuperb

    docsuperb New Member

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    As if trying a tight turn at low speed with overtight Look Keos and paying for it with a sore knee and high embarrassment factor wasn't punishment enough, I've now discovered I must've bashed the rear derailleur when I hit the deck. This is annoying for two reasons:

    1. It's not the first time I've had gear problems after a crash
    2. I don't really know what the problem is.

    I've got a 9-speed Ultegra rear mech (original 2004 Bianchi ML3 issue) and I suspect the derailleur has been bent inwards (when I'm in the lowest gear, the cage is now knocking against the spokes).

    What I'd like to know is whether I should try and fix it myself (if so, how); should I take it to a shop and get them to repair it (probably looking at, say, £50 for the job) or should I just get a replacement rear-mech (as it's seen about 5000km+ anyway).

    Any thoughts appreciated - apart from comments on my cycling ability :p

    Cheers
     
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  2. alfeng

    alfeng Well-Known Member

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    If your bike's frame is steel, then YOU can align the derailleur hanger ...

    • Either use a fairly large (10" to 12") adjustable crescent wrench OR a similarly large pipe wrench + two pieces of scrap plywood-or-equivalent to prevent marring the SOFT metal of the dropout-and-derailleur-hanger
    • Use about what you estimate to be 5 lbs of force ... BE GENTLE ... the metal is softer than you might think ... with the leverage, it will be almost as yielding as an inexpensive wire coat hanger.
    • Repeat as necessary.

    You can CHECK for alignment by taking a piece of very STIFF cardboard or small piece of scrap of whatever is handy that you have and attach it to the derailleur hanger with some packing tape if you don't have a 10x1 bolt -- when the hanger is aligned the scrap should be parallel to the bike's central plane and/or rear wheel (presuming that the wheel is true).

    NB. If the frame's derailleur hanger is alloy, then you will need to replace it sooner-rather-than-later!




    .
     
  3. vspa

    vspa Active Member

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    it could well be the frame dropout the one with damage, in that case a new mech won't solve it,
     
  4. docsuperb

    docsuperb New Member

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    Thanks.

    It's an aluminium frame and has a replaceable hanger (onto 3rd one now).

    The hanger itself has some play in it so wonder if I should start with that and at least try and tighten it up first.

    Thanks for the reply.
     
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