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for the first time I am doing basic drivetrain maintenance and I noticed slight play in my rear Shimano XT 12SPD mech. It does not occur at the place where the derailleur is connected to the hanger but elsewhere. I marked it on the image (https://i.imgur.com/gDWjizm.png and also below the text) . Is it normal or is it something I should worry about?

Here is a video: https://youtube.com/shorts/d01kTdtmv8c?feature=share

thank youenter image description here

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  • Does it work ok?
    – David D
    Commented Dec 31, 2023 at 20:56
  • Well yes. When I was riding, I didn't notice anything weird. I was just surprised it moves there, as well and don't know what it is.
    – samokosik
    Commented Dec 31, 2023 at 21:57

2 Answers 2

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Some play in this area, which is kept static under chain tension, is normal.

Problem areas where play can develop would be in the parallelogram pivots, which would affect accuracy. That failure mode is commonly seen at Altus/Alivio/Claris/Sora level but the higher models are generally more reliable.

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  • That makes me calmer. May I ask, though, what are parallelogram pivots?
    – samokosik
    Commented Jan 1 at 21:25
  • First search on the term "parallelogram" using a web search engine. Parallelogram is a geometry term, and the images that come up are a traditional parallelogram shape. Note, even a square is a parallelogram, but not what is first though of when the term is used. Now look at your rear derailleur, the part that moves side-to-side to move the chain from one cog to another. That part of the rear derailleur pivots on four pins/pivot points to move the chain back and forth on the cassette. THAT is the parallelogram, and the pivot points it pivots on are the points you are asking about.
    – Ted Hohl
    Commented Jan 2 at 2:14
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The rotation of the derailleur at that point (that area is the "B-axle" of a derailleur) is normal. Although it does not rotate at this point in normal use, it can allow the derailleur body to swing up out of the way of an obstacle it encounters on a trail.

One thing to note about these types of derailleurs and this area involves the inner, thin piece just outside the derailleur hangar. The piece just inside your area of rotation. This is called the B stopper plate and a projection on its inside is to rest on the B tension stop of the derailleur hangar (that's the little terminal tail at the bottom of the bikes derailleur hangar). So it's good to occasionally check that the tab on the stopper plate is in contact with the derailleur hangar. Certainly check this situation when running down any shifting troubles that may come up.

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