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I recently changed the rear tire and paid no attention to the original working state of the rear derailleur. After a miserable attempt at resembling, I lost what I now think was the Derailleur bolt and nut (one flat side, curved elsewhere) during a short ride. It's since been replaced with whatever nut and screw I could find laying around.

Like the first attempt (with all the original parts still available) at reattaching the wheel, after a hard pedel, especially uphill, the wheel will move from centered. The tire rubs against the frame creating enough resistance to make pedaling feel impossible.

The rear dropout has a small screw hole and a large triangle cutout. I cannot find a configuration that allows the derailleur to screw into the small hole, and so am fastening it using the larger triangle.

Is the placement of the derailleur the problem? Do I just need to turn the nuts holding the axle on a little harder?

after the axle has slipped down: derailleur position worn nut rubbing against the wheel

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It sounds to me like you've worked yourself up into a state of confusion. I'd recommend going to your bike shop and asking them to sort it, if only so that you have a reference point for next time. It is a trivial job so won't cost much. –  PeteH Jul 29 at 6:42
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In the future you should not disassemble any part of the derailleur to remove the wheel. You just need to loosen the two axle nuts. –  Blam Jul 29 at 14:14

3 Answers 3

up vote 4 down vote accepted

You've lost the derailleur hanger mounting nut. Don't worry, they're dead cheap. Without it the hanger won't stay in place without the wheel nuts done up tight. You can get away without one (see matt's answer), but it's not ideal. It's better and less fiddly to use a proper mounting nut:

Derailleur hanger mounting nut

enter image description here

The way you've set it up now is totally wrong - the triangle-shaped hole is just a cutout in the rear dropout - it isn't designed to have anything mounted to it. I presume the other hole of which you speak is a mudguard or rack mounting eye.

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awesome pictures! –  rusl Aug 30 at 8:16

That configuration is quite dangerous and clearly wrong. Do not ride the bike like that. Do not just tighten the nuts.

I can clearly see the outline of where the derailleur was previously mounted. The derailleur should be mounted in a similar position. The small screw hole is a mount point for a carrier, which is probably why you cannot get things back how they were - it should be clear of obstruction when the wheel/derailleur are assembled.

The axle must sit fully within the drop-outs of the frame. Once the axle is done up properly it will hold the derailluer, the small screw is really a locating screw and used to hold the deraulleur when the wheel is removed.

Undo the right side nut fully, and install the wheel using the left nut to hold it reasonably firmly. Use the marks on the frame to guide you to axle location and center the wheel rim on the brakes/frame. From there, the derailluer should be able to be slotted in and the right hand nut tightened.

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Sorry was unclear. The image was taken after the axle had slipped down. I was tightening the nuts in the opposite order you suggested. Order makes a difference :) –  Will Jul 30 at 15:15

I had a similar problem with an old steel-frame bike that I "rescued." It had sliding dropouts so that the wheel could essentially be positioned forward or rearward as needed. What would happen is that the nut would come loose and one side of the axle would slide forward in the dropout causing the rub.

My solution: A small lock washer or nut on the other side of the dropout and cranking the nut really tight. That worked, although it made wheel removal kind of a pain. I ended up selling the bike before I found a better, more permanent solution though.

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