Chain slipping off the jockey wheels

mitchgixer6 Posts: 729
edited August 2018 in Workshop
Hi all

Had a DNF last night night in a club TT. Eventually I lost a jockey wheel some how. That's what ended my race.

Changing into the small chainring the chain jumped off the jockey wheels and jammed in the rear mech plates. This happened twice, the 2 times I went for the 34 ring. Obviously realised there was an issue with the shifting so rode the rest of the race in the big ring. Eventually though I had to stop as the upper jockey wheel eventually came clean off.

Anyone have any ideas on why this might have happened? Possibly the bolt had came loose giving the wheel too much lateral play? Just wanting to explore all options to try and prevent it happening again.

Thanks folks.


  • fenix
    fenix Posts: 5,437
    It'd be a heck of a coincidence to have another issue as well as the jockey wheel.

    If that's fixed that should be it sorted.
  • keef66
    keef66 Posts: 13,123
    In 50 years of cycling I can't say I've ever encountered a chain jumping off a jockey wheel or a jockey wheel going missing completely. Indeed the only issue I ever had was rounding off the little hex sockets when trying to dismantle a cage and remove the jockey wheels for deep cleaning / lubrication (I ended up buying a new mech more cheaply than I could find the spare parts...)

    Can't think of any explanation other than the one you've come up with; the bolt was working it's way out, allowing the cage to splay apart and the chain to slip off the jockey wheel. Not sure why that should have been worse in the small ring with presumably less tension though...

    New jockey wheel, bolt, threadlock?
  • My CX has been playing silly whatsits recently with the chain periodically coming off the upper jockey wheel and running between it and the side plate. The bike was still rideable, only causing enough drag to slow me down my 1-1.5mph, and there wasn't much in the way of noise that I could tell.

    Once I realised what was happening I put it in the workstand and had a closer look. The bolt wasn't exactly tight, nor was it ready to fall out, but there was some side-to-side play in the bearings regardless. Only a couple of mm, but with the teeth being worn (the bikes done about 8000 miles in mostly winter riding) it was probably enough to cause the chain to occasionally miss engaging with the teeth causing it to slip/drop off the side.

    Fitted some new jockies last night and the commute into work today was noticeably quicker, quieter, and with the chain still where it should be.
  • fenix
    fenix Posts: 5,437
    My mates badly maintained rear mech exploded on a hill once. I think it was the bolts on the jockey wheels that went. We had jockey wheels flying past our heads like Martial Arts throwing stars.
  • Thanks for the replies folks. Can only presume its been a loose bolt. To be honest it's not something I ever check, but will put it down to experience and start checking from now on.

    Super weird as the bolt which was still attached was mega tight to get off....