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I have just installed a new rear derailleur (Shimano Acera - RD-M360-SGS), and I feel like that the pulley has a weird angle (image below). It does shift but not sure if it's healthy. Any idea what could've gone wrong? Is it just a faulty item?

Edit (reason for installing new derailleur): The derailleur hanger got bent, shifted down to 1 on the way home and the derailleur got pushed into the spokes: derailleur was beyond repair, but spokes survived. My local shop straightened out the hanger for me

enter image description here

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    Hard to tell for sure from the picture, but it looks like something is bent. Why did you replace the old one? – Daniel R Hicks Oct 11 '20 at 14:02
  • the derailleur hanger got bent, shifted to 1 and the derailleur got pushed into the spokes: derailleur was beyond repair, but spokes survived. My local shop straightened out the hanger for me. Now that I took it apart again it seems like there should remain some bend though... – amateur Oct 11 '20 at 14:21
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    Yeah, probably the hanger is still a hair bent. – Daniel R Hicks Oct 11 '20 at 14:41
  • Replaceable derailleur hangers are usually very affordable and easy to swap in if you can find a matching one. Looks from the photo like yours is replaceable, I think. – Armand Oct 11 '20 at 21:19
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Often a bent derailleur will kick the bottom of the cage inwards. In your case the derailleur is twisted around the vertical axis so the 'front' edge of the cage is pointing outwards.

The first thing I'd check is that you do not have the mounting bolt cross-threaded.

I'd also take the derailleur of the frame and check that that it is not bent.

The hanger may not have been properly straightened, and it might still have a vertical axis twist. Did the shop use a proper hanger alignment tool? Using a proper tool with ensure the threaded bolt hold is parallel to the wheel axle.

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  • Thank you (and all of you) for the helpful comments. The mounting bolt is not cross-threaded (very happy) and the derailleur is straight as much as I can tell (the pulley is parallel with the mounting bolt). The shop didn't use an alignment tool, but I don't blame them as they offered to just hammer it out (for free) after I bought the replacement derailleur... In any case, I see that the hanger is still bent so I'm working on fixing it. Thanks again!! – amateur Oct 11 '20 at 20:03
  • @amateur: The safest way would be to get a new hanger. Bending a hanger back might damage the structure of the metal and cause it to snap unexpectedly. Consider a hanger like a fuse in an electric circuit that blows to protect the circuit from overload. Also, if the RD was caught by the spokes, keep an eye on them. Some may still snap long after the incident. – Carel Oct 11 '20 at 20:13
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Some modern derailleurs indeed come purposefully bent from the factory, but yours doesn’t look right. I think your hanger is bent inwards, but it’s hard to guarantee that from a photo.

Try removing the hanger and placing it on a flat surface, like a piece of glass or something. Shine a light from one side and see if you can see light peeking out from underneath, indicating a bend.

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Looks bent but could be optical distortion from the camera. Did you watch the mechanic bend back the derailleur hanger? They should use a special derailleur hanger alignment tool which makes sure it’s straight, not just eyeball it. It would be very unusual for a new derailleur to come bent out of a sealed box.

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    Even without the special tool the mechanic should be able to reach into his box of spare parts and pull out, I'm thinking, a front axle that has the same diameter and thread as the hanger bolt. Screw that in with a lock nut and you have a very good indicator of "straight", plus it's easy to put a pipe over the axle to convince it to move in the proper direction. – Daniel R Hicks Oct 11 '20 at 16:30
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    @DanielRHicks: That’s my point, a front axle will work for a rough alignment, but I’d expect a mechanic to do better. They should at least use a whole front wheel (instead of just the axle) which makes eyeballing much easier. – Michael Oct 11 '20 at 17:56
  • How many times have you done this? – Daniel R Hicks Oct 11 '20 at 18:14
  • @DanielRHicks: Once, with a whole front wheel. – Michael Oct 12 '20 at 5:28
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Maybe the derailleur shaft (axle, pivot) or hook (the frame's hanger for the derailleur) is curved.

It is not healthy for the chain rollers and will increase wear over time.

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