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I have had issues with noisey drivetrain and inconsistent shifting despite indexing adjustment. I have found wear on the top jockey wheel cage, is this normal or should the chain not rub here? Does this indicate a bent derailleur / hanger? derailluer

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  • Since that is the top I am not suspecting bent derailleur. Is there a shim/space on that pulley on the wrong end by any chance. Do you have room to put a spacer in? Is the chain by any chance the wrong size? – paparazzo Sep 10 '14 at 19:40
  • To the best of my knowledge (i don't have it in front of me) there are no spacers, there is play side to side in the guide pulley but not sure how much is within spec, it has not had much use from new. Chain is as fitted new, a side plate fractured on the chain so it has a powerlink in it – ultimate Sep 10 '14 at 19:49
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    LBS have confirmed it is normal and only contacting on upshifts which apparently is normal – ultimate Sep 11 '14 at 17:13
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In my experience it is usually the derailleur hanger that gets bent. After all derailleur hangers are built to be the weakest point so that in case something hits the derailleur neither the frame nor the derailleur is damaged. The hanger is just a 15$ part.

There is a derailleur hanger alignment gauge, which bike shops use to check whether the hanger is bent:

http://www.parktool.com/product/derailleur-hanger-alignment-gauge-dag-2

One can even use this tool to bent the hanger back if it is only slightly offset. If you ask nicely and come with the derailleur unscrewed your lbs should check that for free, it only takes 2-3 minutes.

If the hanger is ok then the derailleur might indeed be bent. But the first thing to check is the hanger.

(All this advice under the precondition that the derailleur was correctly mounted, adjusted and only matching components have been used (no 10 speed shifter on a 9 speed drivetrain, no different generations in the parts, only compatible SRAM/Shimano mixup, etc.)

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I'd say that yes, that indicates a bent derailleur. A bent hangar would cause faulty shifting, but wouldn't cause wear like that. That wear implies that the chain line off, and the chain is rubbing the derailleur cage.

There's a chance you can just replace the cage/pulleys and fix the problem, but I'm not sure.

If you remount the derailleur is there any visible misalignment? The cage should be straight, and the pulleys should be in line with each other and should rotate in the same plane (e.g. they shouldn't be cock-eyed with respect to one another).

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