derailleur bumping into sprocket - was functioning fine before the ride

distro_dave

My son’s Shimano Deore XT rear derailleur (Shadow Plus, Dyna-Sys 11) was shifting fine before his ride, but after finishing, the entire derailleur is rubbing against the rear sprocket. This is not just a minor misalignment—the derailleur itself is making contact with the cassette. I understand that common causes of derailleur misalignment include: • A bent derailleur hanger • Improper derailleur installation • Incorrect B-tension screw...

Originally asked by bonhoffer on Stack Exchange (bicycles) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

I guess it's the broken part in your second image. This is the notch against which the derailleur's B screw levers to set the distance between derailleur and sprockets. Looks like there's a new derailleur hanger needed. As suggested by Criggie in the comments you might also want to inspect the derailleur itself if it has taken some related damage. Take a special look at the B screw and its surroundings. Does the part where the screw is threaded through look broken or bent? Can the screw be operated easily or does it seem to be stuck somehow? Does the direction in which the screw points look somewhat "off"? When in doubt it might be a good idea too have some bike shop inspect the thing. They...

Full answer by Benedikt Bauer: https://bicycles.stackexchange.com/a/96303 (CC BY-SA 4.0).

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