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B-screw adjustment not working

FSPTNFSPTN Posts: 13
edited July 2018 in Workshop
Hi, I just installed a new cassette on my bike and now the guide pulley, chain and largest rear cog are all rubbing together at the back when I'm in the smallest chain ring and largest sprocket. When I tighten the b-screw the wee "pivot" with protruding notches, which I think is supposed to contact the derailleur hanger, is just sliding past in both directions. Does anyone know how to fix this? I'm not totally sure how it works but as far as I can see the wee notch is supposed to catch the hanger and then the derailleur body will change angles. I tried tightening the derailleur mounting bolt but it didn't push it on any further. The hanger looks straight to me but it could be a hair off line.

Any help appreciated.

Posts

  • cooldadcooldad Posts: 32,601
    Try a picture.
    I don't do smileys.

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  • jgsijgsi Posts: 5,029
    Without the aid of pictures and reading your subjective description, it sounds like you have cross threaded the rear mech.
    If this is a like for like replacement then its user error and a new hanger.
  • If the B-screw is missing the hanger laterally, I could only assume that the rear derailleur is not fully tightened onto the hanger.

    If you're suggesting that the B-screw is not having an impact on the clearance between the jockey wheel and the cassette, firstly ensure that the B-screw is fully screwed in, if there is still insufficient clearance - try removing the B-screw and screwing it in from the underside - letting the head of the screw make contact with the derailleur hanger - this trick normally allows for another few teeth on the cassette than officially advertised.
  • laurentianlaurentian Posts: 1,890

    If you're suggesting that the B-screw is not having an impact on the clearance between the jockey wheel and the cassette, firstly ensure that the B-screw is fully screwed in, if there is still insufficient clearance - try removing the B-screw and screwing it in from the underside - letting the head of the screw make contact with the derailleur hanger - this trick normally allows for another few teeth on the cassette than officially advertised.

    Alternatively, buy a longer (1") screw.
    Wilier Izoard XP
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