Chain jumping off lower jockey wheel?

JesseD
JesseD Posts: 1,961
edited March 2016 in Workshop
I have just replaced the cassette, chain, outer chainring and rear mech on my bike, they were all Shimano 5800 and have been replaced with the same, apart from the rear mech was a medium cage and is now a short cage one.

I was setting up the indexing on the rear mech and noticed the chain was not sitting properly on the lower jockey wheel and was sitting on the outside of the wheel slightly, this is happening despite the indexing being spot on, the problem also seems worse in the big ring but still happens whilst in the little ring?

Any ideas what may be causing it?
Obsessed is a word used by the lazy to describe the dedicated!

Comments

  • sungod
    sungod Posts: 16,891
    is the wheel fully seated in the dropouts? (loosen qr, put weight over bike, tighten qr)

    is the chain length correct? (follow shimano instructions for the exact model of rear mech)

    is the mech hanger loose/bent? (ideally use alignment gauge)
    my bike - faster than god's and twice as shiny
  • JesseD
    JesseD Posts: 1,961
    sungod wrote:
    is the wheel fully seated in the dropouts? (loosen qr, put weight over bike, tighten qr)

    is the chain length correct? (follow shimano instructions for the exact model of rear mech)

    is the mech hanger loose/bent? (ideally use alignment gauge)

    Hi Sungod,

    I have double checked the wheel alignment and it is sitting properly, I have checked the chain length as well and that is also good. Upon looking at the mech from the back I fear it maybe a little twisted which leads me to thing either the cage is bent or the mech hanger is bent, and given its a new mech then my money is on the hanger.

    I am taking it into my LBS this morning to get the alignment checked as I don't have the tools and hopefully it is and they can sort it easily as I am racing tomorrow morning!
    Obsessed is a word used by the lazy to describe the dedicated!
  • JesseD
    JesseD Posts: 1,961
    My bet was on the rear mech hanger, took it to the shop and he pulled out a big adjustable wrench and bent the cage a bit and voila perfect shifting!

    Apparently its a well know issue with Shimano rear mechs!
    Obsessed is a word used by the lazy to describe the dedicated!