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new chain skips on jockey wheel

i have replaced a shimano 9 speed chain with kmc 9 speed. It is routed correctly and changes up/down ok (11-28 rear 50-34 front) but the chain slips off jockey wheel when pedlling - worsewhen in small chainring. I read on another post abot mtb 3x9 set up that someone had similar issue but was not sure if it was fixed bt replacing cassette.

I have tried with another wheel /cassette (11-28) same issue - although both cassettes are not new.

If i put bike upsidedownand spin pedals i can "fix" issue by holding jockey cagecouple of mm outwards. However there has been no change/damage/etc rear derailleur.

Any ideas ??


  • bondurantbondurant Posts: 858
    It sounds like your gears need re-indexing, even though you say nothing has changed. If the chain is coming sideways off the jockey wheel, when the jockey wheel should be directly underneath the sprocket it feeds, then it needs re-aligning.
  • DeVlaeminckDeVlaeminck Posts: 8,466
    Have you had the jockey wheels out at all?
    [Castle Donington Ladies FC - going up in '22]
  • mr.colinmr.colin Posts: 5
    no jockey wheel not been changed.
  • mr.colinmr.colin Posts: 5
    the only thing changed was the chain - and had to slightly increase cable tension using barrel adjuster to get gears indexed.
  • bondurantbondurant Posts: 858
    I'd start over with the indexing.
  • focuszing723focuszing723 Posts: 6,005
    I'm sure you have, but make sure the chains are the same length.
  • david37david37 Posts: 1,313
    causes given you can force it a couple of mm and the problem goes

    bent hanger - check and straighten

    bent derailleur - look directly down through cassette and jockey wheel should be straight. bend back to achieve straight or replace

    if its only at either end of cassette check the limit screws are set properly

    ensure no contact between derailleur jockey wheels and cassette. - adjust b screw accordingly

  • mr.colinmr.colin Posts: 5
    the good news is that tweaking limit screws has stopped the rattle....but somehow i have can no longer get into 13-11 sprocket - although to be honest i am not fit enough/strong enough to need them!

    so probably ride as is until local bike shop re opens its workshop!

  • PMarkPMark Posts: 153
    If you didn't have this issue before you changed chains, then it will probably ether be the cassette or front chain ring is worn.

    Had this issue 2 years ago when I installed a new chain at the same time as getting some new wheels. I initially though it was the wheels, but problem was there on my old pair. I then went around changing everything trying to fix it:
    -rear derailleur (although I upgraded to one that supported 34t so wasn't a total loss)
    -rear cassette
    -derailleur hanger
    -chain (again)
    -gear cables
    -front derailleur
    -then finally got a whole new crank with chain rings and that solved the problem (I could of just changed the chainrings, but thought I might as well get a shinny new crank at the same time).
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