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I have a fairly new Shimano rear derailleur on a cheap department store MTB a friend gave me. Recently the derailleur (particularly the jockey wheels) have started to rub against the chassis in high gears. I tried reseating it on the hanger at a larger angle, but even as far as it will go, it just wants to spring back until it hits the chassis. The best I can get it has it with very little clearance.

Here are some pictures:

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Zoomed in so we can see the derailleur hanger (with "Hole A") that is bolted to the frame. It doesn't move when the axle is loosened.

enter image description here

I don't particularly care for the paint job, but I do want it to stop hitting against the chassis and risk affecting operation. How do I fix it?

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2  
You mounted it wrong - the derailleur should "tuck back" like in this picture: bikebuyers.com/images/rover_26_7_speed_women_red_derailleur.jpg –  Batman Jun 1 at 21:31
    
The other factor is chain length. At a short chain length it will not wrap as far. You don't want to take out too many lengths as then it will now have enough length to go over largest gears in front and back. –  Blam Jun 1 at 21:46
    
Definitely something is screwed up. Compare to this image where the chain is on about the same cog. It may or may not be mounted wrong, but it looks pretty likely that the chain is too long. The chain should just barely be long enough to fit the two largest cogs with the derailer fully stretched out. –  Daniel R Hicks Jun 1 at 22:00

3 Answers 3

To clarify, these Shimano Tourney derailleurs have their spring-loaded pivot at a different place to where they attach to the derailleur hangar. Pivot B is not a pivot at all, and shouldn't be free to move. However, it is currently attached at the wrong angle. The angle made between the hangar and the rigid part of the derailleur should be more acute, as in this image.

Correct mounting of RD-TX55

Note that there is a protruding tab on the derailleur's attachment point, and on the hangar itself. These tabs should be pressed against each other, such that the arrangement prevents that part of the derailleur from rotating in an anticlockwise direction relative to the hangar. I've highlighted the tabs that need to mate together in the image below.

Derailleur and hangar tabs highlighted

You may need to fine tune the chain length and derailleur adjustment further, follow the Shimano service instuctions for RD-TX55.

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Your chain is too slack. Get a chain breaker tool (the cheap ones are about ten bucks) and shorten your chain by about three or four links.

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I am going to post my comment as an answer so you don't just start taking out links

Put font and rear on the largest gears
From there take out links
If you take out too many links then it won't have room to go on the largest path

If the hanger is not really designed for that bike you might have a case of you can't take out enough links
But not all the bad - I bet if you have the front derailleur on the bigger gear you can put the rear on the smallest - so you do have access to the tallest gear

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