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Rear derailleur hanger - stripped threads

GarryboyGarryboy Posts: 344
edited January 2014 in Workshop
Hi all,
I had an off a couple of weeks ago, right hand side down, rear derailleur took a hit and hanger bent.
I managed to pull it back into line and bizarrely the gears seem ok.

However, I wanted to replace it, but in haste I've managed to strip the thread (head) on one of the bolts that attach the hanger to the frame. It's basically rounded.

I can live with it for now and could poss use a hanger alignment tool to tune it, but it will need to come off eventually!

Any tips?

Posts

  • majormantramajormantra Posts: 2,094
    Are the threads in the hanger or the frame? If the former (which is more common), you might just be able to break the bolt and push the remains out of the hole in the frame. If the thread is in the frame, you'll have to figure out a way of extracting it properly, I would think. A bit tricky with such small bolts.
  • GarryboyGarryboy Posts: 344
    Cheers - the bolt goes into the hanger first, then the frame.

    It's a carbon frame (alloy dropouts), so bit worried about using too much force (perhaps unnecessarily worried).

    The bolts are really small, but have pretty wide heads
  • majormantramajormantra Posts: 2,094
    That would mean threads in the frame.

    Could you cut a slot in the bolt head with a Dremel type disc, perhaps?
  • just drill the head off bolt with a drill 0.1mm smaller than the bolt diameter. then the remaining shank of the bolt should just unwind out.
  • keef66keef66 Posts: 13,123
    So was it a small hex socket in the screw head? Presumably countersunk so it's flush with the face of the mech hanger when installed?

    Best bet is to get hold of a suitably sized screw and stud extractor bit. Carefully drill a pilot hole into the centre of the screw, then follow that with the stud extractor. Once it starts to bite it should free the screw.

    Or if you don't want the hassle / expense / fear of breaking it yourself, any self respecting LBS should be able to do it in a couple of minutes.
  • GarryboyGarryboy Posts: 344
    Thanks all, I guessed a drill might come into the equation!
    Was also gonna have a try with a torx key, one size up from the hex key size - will have a go this weekend
  • keef66keef66 Posts: 13,123
    Garryboy wrote:
    Thanks all, I guessed a drill might come into the equation!
    Was also gonna have a try with a torx key, one size up from the hex key size - will have a go this weekend

    That's always an option; tap it in so it bites a bit before you try to turn it.

    Tiny hex sockets always make me nervous; I've replaced the bottle cage bolts on my winter bike for ones that take a larger allen key.
  • crankycrankcrankycrank Posts: 1,830
    Garryboy wrote:
    Was also gonna have a try with a torx key, one size up from the hex key size -
    Yes, try the torx first before breaking out the heavy machinery. If this fails try drilling just the bolt head off, remove the hanger and you may have enough exposed bolt to twist off with some pliers.
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