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  1. #1
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    Derailleur hangers breaking for no reason?

    While trail riding today, the derailleur hanger on my FS bike broke, for no apparent reason. I didn't get a branch caught in the drivetrain, I didn't hit a rock, and the chain didn't bind up in the cassette. It just snapped, and not even under a great deal of pedalling force.

    This ever happen to anyone else here? The only thing I can think of is that it wasn't a factory hanger, but an aftermarket brand (NSB - North Shore Billet). It wasn't even that old - maybe a few months, with very low mileage.

    Any ideas on this?

  2. #2
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    If you checked and can't find the reason then it's just one of those freak incidents. Replace the hanger, if it breaks a again then you've overlooked something. At least that's what I'd do.

  3. #3
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    They break for a reason, even if the reason isn't apparent later.

    Among the common reasons for breakage besides those listed and putting the RD into the spokes, are a stiff link binding as it goes through the RD cage (you won't feel this happening), or the B screw set to close so the upper pulley touches the sprocket through the chain.

    Note also that a hanger can break long after an incident. The first rock or shock bends or partly cracks it, then it takes a second incident of much lower force to part it. In some cases vibration alone can part a cracked hanger.

    breakaway hangers are a trade off, since they have to be made intentionally weak so as to reliably break before the dropout, and maybe even before the RD.

    When you but your replacement, buy a spare at the same time, then make sure all is 100% when you finish the installation, and inspect the new one from time to time.
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    The key to solving any problem is to understand and address the underlying cause.

  4. #4
    Give it a crank
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    One more thing that can break a DH is chain that is too short. When you go put it on the big ring and big rear sprocket, if the chain is too short, the DH will be instantly history. There are many ways to get a short chain, some are: chain repair that eliminated some links, replacing a crankset with larger rings, replacing a rear derailleur, and other surprises.

  5. #5
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    I think the bigger issue is what the OP stated and that it is not the original hanger, but a billet piece from an aftermarket company. Id be willing to bet they used an inferior aluminum to machine the product.

  6. #6
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    Quote Originally Posted by Mtn-Rider View Post
    One more thing that can break a DH is chain that is too short. When you go put it on the big ring and big rear sprocket, if the chain is too short, the DH will be instantly history. There are many ways to get a short chain, some are: chain repair that eliminated some links, replacing a crankset with larger rings, replacing a rear derailleur, and other surprises.
    I could see that being a possible cause, but I've been running the same setup on my bike for a number of years.

    Quote Originally Posted by FBinNY
    Among the common reasons for breakage besides those listed and putting the RD into the spokes, are a stiff link binding as it goes through the RD cage (you won't feel this happening), or the B screw set to close so the upper pulley touches the sprocket through the chain....

    When you but your replacement, buy a spare at the same time, then make sure all is 100% when you finish the installation, and inspect the new one from time to time.
    Might have been a stiff link - there was one that seemed to bind a little bit.

    Definitely going to buy a spare to carry with me - I normally do have one in my pack, but I forgot that time.

    Thanks to everyone for the answers. Much appreciated.

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