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My rear deraileur is bent. How to fix?

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My rear deraileur is bent. How to fix?

Old 10-14-06, 12:14 PM
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Torellian
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My rear deraileur is bent. How to fix?

I just got back a mtb that was stolen from me 1.5 years ago----click to read about it http://www.bikeforums.net/showthread...92#post3217292

I noticed that, among other things, the rear deraileur is slightly bent inward. It seems to be bent at the place where it is attached to the frame. There is no way to get proper leverage to try bending it back while it is still on the bike, so I thought taking it off would be of help, but I'm not experienced in such things and have never removed major components before. There is a big bolt in the center that looks like it attaches the whole thing to the frame by the rear hub. Would removing this bolt remove the deraileur, and is anything their under any kind of tension that would be released upon its removal? I'm hoping it's a simple bolt off/bolt on kind of thing. Should I do this, or is it best left to a mechanic?

When I try riding, the chain sometimes shifts from the gear I'm on to the next one and back again without me wanting it to. I thought maybe the deraileur not being lined up right might be causing this.
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Old 10-14-06, 12:40 PM
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San Rensho 
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Sounds like a bent der hanger.

If its a steel frame, you can bend it back. Put an allen key in the bolt that holds the der onto the hanger, grab the allen key with a vise grip and bend the hanger back into place.

Or, remove the der, and use a a very large adjustable wrench to grab the hanger and bend it back.
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Old 10-14-06, 02:14 PM
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Originally Posted by San Rensho
Or, remove the der, and use a a very large adjustable wrench to grab the hanger and bend it back.
Bad, bad, bad idea. Trying to realign the derailleur hanger without a bolt of somekind in the hole can ovalize the mounting hole. I don't know how to fix it after that happens.

I've been successful in clampong a big crescent wrench over both the derailleur and hanger to bend it back straight. If the OP has a 9 or 10 cogs on the cassette, they're pretty picky about proper alignment. He'll probably be better off with having a shop use the correct tool to realign the hanger.
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Old 10-15-06, 10:56 AM
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Originally Posted by Retro Grouch
Bad, bad, bad idea. Trying to realign the derailleur hanger without a bolt of somekind in the hole can ovalize the mounting hole. I don't know how to fix it after that happens.

I've been successful in clampong a big crescent wrench over both the derailleur and hanger to bend it back straight. If the OP has a 9 or 10 cogs on the cassette, they're pretty picky about proper alignment. He'll probably be better off with having a shop use the correct tool to realign the hanger.
How can it damage the threads? The adjustable is grabbing the entire hanger and bending it from where it attaches at the drop-out.
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Old 10-15-06, 04:37 PM
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I think Retro Grouch meant that the derailleur bolt hole would be warped so as to be not perfectly circular, but I also think it sounds like your method is performed with a bolt in the hole...
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Old 10-15-06, 04:45 PM
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Either get yourself one of these http://parktool.com/products/detail....=48&item=DAG-1, or take it to a shop. Shouldn't cost you too much to get it fixed.
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Old 10-16-06, 10:23 AM
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To clarify my situation, my frame is aluminum. And it looks like it is the deraileur hanger that is bent. The number of gears in the rear cassette is 8. The chain keeps skipping back and forth from 1 gear to another and back again while I'm pedaling.
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Old 10-16-06, 04:31 PM
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Aluminum takes less kindly to bending back than steel does. The question is: "Can you ride it the way that it is?" If the answer is no, then you have nothing to lose by trying. The "A" way to do it is with a derailleur hanger guage tool. You might be able to get it close enough by clamping the mother of all adjustible wrenches over the derailleur and hanger together.
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Old 10-16-06, 06:17 PM
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By any chance do you have a detachable derailleur hanger? Aluminum frames most often do have a separate, detachable, replaceable hanger. It might be a cheap and easy fix.
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Old 10-17-06, 12:38 PM
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I just got back from the bike shop. They took a look at the derailleur and everything else on the bike and concluded that a good tune-up would be in order. The crank in front is also making a loud metalic "ping" when I pedal, so that also needs to be dealt with. He said everything together should cost about $60. He said the bike still looks like it's got plenty of life left in it, so I guess I'll go for it.

Thank you all for your advice on my situation. I was hoping I could take care of bending back the deraileur myself, but there seems to be other issues too, so I'll just get it all done at once.
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