Chain jumping off changing to big ring

mitchgixer6
mitchgixer6 Posts: 729
edited February 2019 in Workshop
Hi all.

Been having some issues with my new bike recently. I'm running Ultegra 6800 with a KMC X11 chain.

1 shift out of about 20 the chain will drop when changing from the small ring to big ring and is getting caught between the chain set and chain stay. At first I thought I was unlucky with hitting bumps at the wrong time but yesterday it cost me time in a race so really need to get it sorted.

It's almost as if the teeth don't pick up the chain properly once it his the pick up pins and throws the chain to the inside where it drops off the chain set.

Any ideas what to check? I can't adjust the FD to shift further out or the pick up pins hit the inside of the FD cage, it's at the limit already.

Comments

  • wongataa
    wongataa Posts: 1,001
    It sounds like the FD is in the wrong position and/or the stop screw is in the wrong position if the chain can come of either of the chainrings. The tension could be out too maybe.

    Try disconnecting the shifter cable and removing the front derailluer. Then set it up from scratch using the instructions from Shimano. See the tech docs section of their website for info.

    I once had similar issues when my chain would occasionally come off. I did the above and it has been fine since.
  • mitchgixer6
    mitchgixer6 Posts: 729
    I've done this many times already as I've had a real headache getting the trim to work properly. As it is it's not working correctly with the trim, and the verdict from the LBS is that it'll never work properly. I think the frame is optimised for Di2 so the trim on the FD can't be made to work correctly without modifying the hanger which I'm not prepared to do just now.
  • slowbike
    slowbike Posts: 8,498
    a photo of the FD and how it's set up compared to the chainset would be helpful.
  • mitchgixer6
    mitchgixer6 Posts: 729
    14304225625_a7b2a2889c_b.jpg

    14300875241_25f2738421_b.jpg

    14117690397_078157b27d_b.jpg
  • drlodge
    drlodge Posts: 4,826
    mitchgixer6 wrote:
    1 shift out of about 20 the chain will drop when changing from the small ring to big ring and is getting caught between the chain set and chain stay.

    I don't get this, you say this happens when moving from small to big chainring? I can understand if the chain comes off like this when moving from big to small, but fail to see how the chain can go between the chainring and stays if the FD is pushing the chain *away* from the frame?
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  • mitchgixer6
    mitchgixer6 Posts: 729
    Indeed. It's got me stumped too hence the post. I feel I'm fairly competent with maintenance. I built the bike myself. I installed a chain catcher to avoid it coming off on the inside as you describe.

    It's like the chain get's lifted off the wee ring by the shift pins but doesn't mesh with the teeth so it then drop off the inside of the wee ring where it then get's caught in behind the chainset against the chanstay. I don't think it's the limit screw or the tension. If either of them were out then it would push the chain the other way.

    Bottom picture shows the bike in the biggest 53x11. I can't move the FD much either way or it will rub.
  • slowbike
    slowbike Posts: 8,498
    Sounds very odd.

    With no logic behind what it's doing - ie why doesn't it just not shift rather than fall off the inner ring too - why not change components until it doesn't happen any more?

    First one to do would be the chain itself.
  • mitchgixer6
    mitchgixer6 Posts: 729
    That's what I was thinking to try.

    I did think at first it was because I had a standard gear cable in there instead of the Polymer coated one. It was pretty stiff to shift like that and I thought maybe the FD wasn't moving far over enough, but I installed the Polymer cable last week and it has been much easier to shift. I thought that had solved the issue until it dropped yesterday.
  • jackc6549
    jackc6549 Posts: 30
    I dont mean to doubt/criticize your work but are you sure you installed the reversible cable 'diverter' thingy the correct way for your bike? i'm not sure how relevant it is but its worth checking. I didnt get any instructions with mine so checked the online instructions. i'd originally (before reading the instructions) had installed it incorrectly.

    If its not shifting to the big ring consistently, it sounds like either the cable tension is a bit low or your high limit screw is too tight.

    edit: ah, just saw your pic of 53x11, looks like theres ample tension and clearance for it too shift with no problem.
  • mitchgixer6
    mitchgixer6 Posts: 729
    Thanks for the replies everyone.

    Yes definitely installed the converter in the correct position. It was pretty obvious which way it should go, wasn't as if it was close between the settings.

    Was out for 50 miles today and tested it a fair bit but was shifting perfectly. I get a funny feeling it might be one of these things I never get to the bottom of.......
  • reme-luke
    reme-luke Posts: 122
    Your not the only one mitchgixer6 out today I had the exact same thing happen to me twice ultegra 6800 when moving from small to big ring drops the chain off the inside of the small ring. Never done it before and apart from those two times it shifts faultlessly.
  • mitchgixer6
    mitchgixer6 Posts: 729
    Sorry to hear you had the same issue but glad to know I'm not the only one!

    Out if interest what chain are you running?
  • reme-luke
    reme-luke Posts: 122
    Ultegra 6800 it's a bizarre issue hopefully like you say it's just one of those things and doesn't continue.
  • mitchgixer6
    mitchgixer6 Posts: 729
    I've a funny feeling it's something to do with the lift pins and how they interact with the teeth. But then again Shimano have been making chain rings for long enough you'd think they wouldn't make any errors there.

    I'm just thankful my frame has a metal protection plate for chain suck or else my carbon would be wrecked!
  • PBDav
    PBDav Posts: 1
    Sorry to restart an old thread, but did anyone ever get to the bottom of this? Just started having very similar issues when I replaced my old 2013 Dura Ace 9000 52/36 with exactly the same (52 had worn out). Tried all the same things - reinstalling the FD as per Shimano Dealer Manual, DA chain on correct way round etc. but still having problems.

    Thanks!
  • mugensi
    mugensi Posts: 559
    Have you tried toeing the FD out slightly using the little hidden screw that presses against the seat tube?
  • richp77
    richp77 Posts: 12
    Resurrecting again. Having the same issue when shifting under load from 36 to 52 and the chain falls off inwards. Worn chain rings, chain or toe out the fd? Did anybody find a definitive solution? Thanks in advance.

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