rear dropout alignment

dieselgeezer Posts: 231
edited September 2009 in Workshop
Anyone got thoughts on the following? Carbon frame with replaceable rear dropout. Earlier this year I had a bit of an off & the bike landed on the rear mech. Never gave it much thought until now. Was setting up the rear mech limit screws when I thought I'd measure tha accuracy of the rear mech hanger. In a vertical plane there's about 10mm variation & in the horizontal about 20mm. Should I be bothered about this? Also, as the replaceable dropout is an aluminium casting would it have bent when dropped on the rear mech? or would it have snapped?
-- "I am but a spoke in the wheel of life" -- Ghandi


  • Yes, the alu can bend a little before breaking and yes, it sounds like it needs to be straightened. You'll need a rear mech alignment tool to straighten it properly but there is the chance that the alu will crack or be weakened. If in doubt take it to the LBS. Shouldn't be too expensive for them to do it.
  • Wappygixer
    Wappygixer Posts: 1,396
    A few mil can make a huge difference to gear shifts so yes get it sorted.
    You will need the correct tool like this
    Once you've bought it it will always come in handy.
  • If you do buy this tool, be aware that it uses the rear wheel as a base for adjustment. Your rear wheel therefore needs to be true laterally.
  • Thanks for the info. Just ordered the alignment tool.I assume it's unlikely to snap the hanger or mess up the frame. Fingers crossed!
    -- "I am but a spoke in the wheel of life" -- Ghandi
  • Thanks for the info. Just ordered the alignment tool.I assume it's unlikely to snap the hanger or mess up the frame. Fingers crossed!
    Just try to do as little bending as possible meaning you don't want to overcorrect and then have to bend it back again to get the correct alignment. Alu will only take a few tweaks before it will start to crack. By the way I'm guessing what you're referring to as the dropout is actually called a mech/derailleur hanger. Dropouts are what holds the wheels. Good for you for getting the tool and doing it yourself!
  • methinks you might be better off buying a replacement mech hanger, assuming that is what is replaceable. I would be wary of using such an alignment tool on a carbon bike. I think they are primarily designed for methal frames.
    I have only two things to say to that; Bo***cks
  • alfablue
    alfablue Posts: 8,497
    Isn't this tool really for Ti and steel frames? Almost all Alu frames and all carbon have replaceable hangers, if the hanger is bent, this should be replaced, not use part of the carbon frame to exert leverage to bend it back :shock:
  • generally i'd take the hanger off and hammer it flat...

    then check it. You tend to get non-replacable hangers on ti and steel frames and those can be bent back most of the time.

    Any aluminum hanger i'd bent back i'd also order a replacement at the same time.
  • You still have to make sure that even a new replacement hanger is aligned properly due to the possibility of the hanger mount being bent. Not usually the case but it can happen. The tool is a good investment because just falling over, leaving it to get jostled around at bike racks or throwing your bike in your car your hanger can get bent. I just helped a guy last week who couldn't figure out why his rear mech was so tweaked since his bike has never been down. Turns out he throws his bike in the boot of his car and ties it down tightly with a rope, with the bike resting on it's right side of course. :shock:
  • hmmm, i'd say yes it's a good investment, i use one fairly regularly, but there are much more important things :lol: