Bent rear mech. hanger

Steve I
Steve I Posts: 428
edited January 2008 in Workshop
I clumsily knocked my bike over today and the mech. hanger is slightly bent, enough to throw the gears out of adjustment. Is it feasible to try and bend it back with an adjustable spanner? I was thinking of removing the rear mech. and leaving the hanger in place on the frame. Doing it this way I'd be able to see when it comes straight as I lever it gently.

Comments

  • HarryDd
    HarryDd Posts: 21
    When I've had to straghten the rear hanger (e.g. getting it back after a flight) I've usually just wrapped the rear mech in cloth to save my hands & pulled it out. Not seeing if your damage is the same I'm not sure if the same would work.

    I've heard that when you do straighten it the move should be made in one go (or at least as few as possible) as all bending weakens the metal & the more moves the more damage done.
  • redddraggon
    redddraggon Posts: 10,862
    What material is the frame?

    Is it a replaceable hanger?

    If the frame isn't steel or Ti, and the hanger isn't replaceable you might be a bit screwed.
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  • robbarker
    robbarker Posts: 1,367
    The repair depends on what your frame is made of and whether the hanger is fixed or replaceable.

    If the hanger is replaceable, it's usually best to replace it, although a minor tweak back is OK. If it's fixed, it's relativelty straightforward with a steel frame, scary with titanium, buttock-clenchingly, bannister-chewingly scary with aluminium and impossible with carbon fibre.

    If you need to tweak, Ideally you need to do it with a derailleur allignment gauge - your LBS should have one.
  • Steve I
    Steve I Posts: 428
    Thanks for the replies. The frame is aluminium, as is the replaceable hanger. I've done this in the past on a steel frame with fixed hanger, it's a doddle like you say Rob.
  • Steve I
    Steve I Posts: 428
    Update - and for any future readers. I had a go a straightening the hanger in situ after unbolting the rear mech. It was immediately obvious that the small bolt wasn't going to hold it firmly enough, if I'd persisted I reckon the hollow bolt would have broken. Anyway, I whipped the hanger off the bike and used 2 adjustable spanners to straighten it. It took about 4 attempts and quite a bit more force than I thought it would have. I used the kitchen work surface as a guide and straightened it until it was flat on the surface with no rocking.

    Just put it all back together. The gears are working perfectly and the mech. is hanging down straight as it should be . I've decided though that this is a temporary repair and I'm going to fit a new one ASAP. I reckon it could be a life saver to have a spare one of these with me on rides and the straightened one will do just fine.

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