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  1. #1
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    Rear derailleur cage broken

    Hello,

    At the weekend I did a rear cassette, chain and jockey wheel change. Whilst cleaning the derailleur cage a small piece of metal broke off (as in photo). The result was that the rear derailleur mech is constantly jumping back and forward, and the chain is jamming around the front chain ring. I backtracked and put the original jockey wheels back on however the problem remains. Is it possible that the metal broken from the derailleur cage is causing this? I thought it was just a guide but perhaps it acts as something to do with tension? Any help greatly appreciated.
    Thanks
    Steve
    Attached Thumbnails Attached Thumbnails Rear derailleur cage broken-shimano-alivio-m4000.jpg  


  2. #2
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    I'm sure it is the problem. The broken metal is probably allowing the cage to flex under load which causes the chain to move left/right and that's why you get the jumps.
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  3. #3
    BOOM goes the dynamite!
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    Need an actual pic, but if your cage is broken that would cause the problem you describe.

  4. #4
    EAT MORE GRIME
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    30 bucks for a new Alivio at Chainreaction right now, on sale
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  5. #5
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    Soooo, I replaced the broken derailleur cage but the problem remained. I popped my old chain back on and instantly the problem went away so my front chain rings were worn to the shape of my worn out chain.

    I had my local bike shop change these, who also noticed that the BB was worn out, so I let them replace it also. When I got the bike back the front derailleur wouldn't shift down onto the granny ring. On further inspection the front derailleur is moved fully across and is butting against the frame, adjusting the limit screw won't bring it in any tighter as it looks as though it could do with moving further towards the frame (which it can't without denting the frame). Could it be that the new BB is shorter than the old, thus making the angle of the front derailleur closer to the frame than as before?

  6. #6
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    ^entirely possible the bb needs a spacer or is incorrect size
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  7. #7
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    Quote Originally Posted by captainp View Post
    I had my local bike shop change these...Could it be that the new BB is shorter than the old, thus making the angle of the front derailleur closer to the frame than as before?
    So they offered to fix it for you, only to create more problems that they should have foreseen? Maybe find a new shop too... in the future.

    Regarding the BB width, it should have come with spacers if positioning/chainline is adjustable. And in that case the mechanic should have known to use the spacers. I'm not sure that's the case, not knowing your original chainline to begin with. The FD should not be touching the frame as that is outside the limits of any chaingring, though it is hard to picture it the way its described.

    Imo, this is a problem the shop introduced and they are the ones liable to fix it.

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