Rubbing jockey wheel

StillRolling
StillRolling Posts: 6
edited July 2015 in MTB workshop & tech
My wife has a 2013 Giant Escape – standard in all respects.
Lately the upper jockey wheel of the RD has started rubbing on the largest sprocket (OK on higher gears). I have tried adjusting the b tension screw – tightening it fully, but to no avail.

Now I have reached the limit of my tech knowledge :oops: . Can anyone help?

Tech spec – RD is Shimano Acera, cassette is Shimano TZ31 14-34, 7s.

Comments

  • mattyfez
    mattyfez Posts: 638
    Check your derailleur is screwed into its frame bracket properly, mine managed to work itself loose, (oops! )

    check for bent derailleur bracket.. I think mine is bent or the spring is shot as I have to slack the bolt that holds the derailleur to the bracket off, or when on biggest rear cog, the chain jumps off and gets trapped between the cassette and spokes, even with the H screw maxed out.
  • StillRolling
    StillRolling Posts: 6
    Thanks mattyfez.

    RD seems solid and pretty straight. No obvious damage (memsahib always takes it quite gently anyway) and indexing is fine. Spring may be an option as there seems to be no "stop" to hold back the RD.
  • cooldad
    cooldad Posts: 32,599
    Post some pictures.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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  • The Rookie
    The Rookie Posts: 27,812
    Check that the B-screw is actually pushing on the stop on the mech hanger.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • StillRolling
    StillRolling Posts: 6
    Pictures attached. You can see the b screw fully against the stop, but this doesn't stop the jockey wheel from moving into contact with the low gear on the cassette. Is there some way I can tighten the spring or is there some other adjustment in the mech? (I ask this before I start to dismantle it !!)

    Many thanks
  • coulddobetter
    coulddobetter Posts: 812
    Try a longer b screw .
  • Rightarmbad
    Rightarmbad Posts: 216
    Chain has worn out and elongation is allowing the jockey wheel to rotate up into the cluster.
    Replace chain and cluster as necessary.
  • StillRolling
    StillRolling Posts: 6
    Chain has a 2mm+ stretch over 12 links = reading my Haynes bike book suggests that its time for a new one. I'll try that first.

    Thanks all.
  • The Rookie
    The Rookie Posts: 27,812
    The Mega range freewheel often needs a longer B-screw than base mechs have.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • StillRolling
    StillRolling Posts: 6
    Thanks everyone.
    Fitted a new cassette - 14-28 instead of the oem 14-34 - jockey now not riding on the cassette.
    New chain to follow.

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