Front derailleur chain rub, both ends... after many adjustments
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  1. #1
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    Front derailleur chain rub, both ends... after many adjustments

    Good afternoon guys,

    I have a ~3 year old Colnago C-RS with Shimano 105 front derailleur - I fairly sure it's a FD-5800 since the cranks are FC-5800. I was having some minor chain rub on the large chainring so I decided to fix it. The cable adjuster was max'd out so I decided to just readjust the whole thing. I disconnected the cable, set L & H stops, set cable tension. I've done this now about ten times and I cannot find the right tension so that there's no chain rub on either end. I've done many a front and rear adjustments over the years and never had an issue to get things dialed in right.

    So for now, I've settled for L chain rub since for me it's less annoying. If any of you guys could provide a tip, I'd be grateful.

    JT

  2. #2
    'brifter' is f'ing stupid
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    If the 5800 is set up correctly the big chainring trim will be minimal, then the shift to the small ring, the small ring trim will be much more noticeable, at least a few mm's. Is this what you're seeing? Is the cage parallel w/ the rings? Is the support screw set properly?
    #promechaniclife

  3. #3
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    Maybe give it a little more on the H and L stops?

  4. #4
    'brifter' is f'ing stupid
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    Without seeing the OP's bike it's pretty much worthless to offer any specific advice, and this can cause major problems.
    #promechaniclife

  5. #5
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    For the first ~18 months, I had no chain rub on either end. In the last 6 months or so I had 'some' rub on the big chainring/smallest cog. I would say it was more than normal; it was noisy. That's why I decided to work on the FD. The cage is parallel to the rings; it has never been moved nor shifted position as far as I can tell. It appears as if the cable tension range isn't as wide as it needs to be. I know that's a function of the front shifter and it's 'set'. There's no cable hangup either.

    I'll post a picture of the FD from above or from whatever angle shows the alignment.
    Last edited by hobiedog; 07-04-2020 at 05:51 AM.

  6. #6
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    Quote Originally Posted by mackgoo View Post
    Maybe give it a little more on the H and L stops?
    The stops are set a tiny bit wider than the cable allows. I can move the FD by hand on either end (against cable tension on big chainring end and against spring tension on small chainring end) enough to clear the chain. And I'm not looking for even a 1/32" gap.... I understand that the chain may touch and I can deal with that, but not the significant noise.

  7. #7
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    Quote Originally Posted by hobiedog View Post
    The stops are set a tiny bit wider than the cable allows. I can move the FD by hand on either end (against cable tension on big chainring end and against spring tension on small chainring end) enough to clear the chain. And I'm not looking for even a 1/32" gap.... I understand that the chain may touch and I can deal with that, but not the significant noise.
    If the full throw of the FD due to cable tension isn't far enough, sounds obvious to me, loosen the cable a hair.

  8. #8
    'brifter' is f'ing stupid
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    Quote Originally Posted by mackgoo View Post
    If the full throw of the FD due to cable tension isn't far enough, sounds obvious to me, loosen the cable a hair.
    This will only work on the 'low' side and would make the 'high' side worse.
    #promechaniclife

  9. #9
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    Quote Originally Posted by cxwrench View Post
    This will only work on the 'low' side and would make the 'high' side worse.
    You're right. GCE here. So tweak it by tightening a hair.

  10. #10
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    So for 18 months all's fine? Nothing had been changed? Cable stretch?

  11. #11
    'brifter' is f'ing stupid
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    Quote Originally Posted by mackgoo View Post
    So for 18 months all's fine? Nothing had been changed? Cable stretch?
    Cables do not stretch, ever. Housing compresses, ferrules get seated all the way, but hte cable does not get longer. I would recommend the OP change out his cables and housing as there might be enough wear inside the housing to cause problems. Or...the cable might be just starting to fray in the shifter. It's pretty rare on the front derailleur side but it does happen.
    #promechaniclife

  12. #12
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    Regardless of the mechanism. Take up the slack.

  13. #13
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    Yep, first 18 months hardly any chain rub on either end. I have noticed that downshifting the FD is quite a bit slower now. I'm starting to think it may be cable fray, housing friction or both..... enough that the FD spring can't overcome it on the low end. That would affect the travel range, which is the main symptom.

  14. #14
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    Two things to check:

    Make sure that your lever hasn't somehow shifted on the bar.

    Pull out and inspect the shift cable for fraying at the shifter end. If the lever feels spongy, then fraying is likely.

    Sent from my Lenovo TB-8705F using Tapatalk

  15. #15
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    Can anyone who can remove a tubless tire from a rim stretch a cable if he gets excited on a quick shift?
    BANNED

  16. #16
    'brifter' is f'ing stupid
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    Quote Originally Posted by duriel View Post
    Can anyone who can remove a tubless tire from a rim stretch a cable if he gets excited on a quick shift?
    Do you ALWAYS have to be that guy? Don't you ever tire of it?
    #promechaniclife

  17. #17
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    Quote Originally Posted by cxwrench View Post
    Do you ALWAYS have to be that guy? Don't you ever tire of it?
    I certainly do....

  18. #18
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    Quote Originally Posted by hobiedog View Post
    Yep, first 18 months hardly any chain rub on either end. I have noticed that downshifting the FD is quite a bit slower now. I'm starting to think it may be cable fray, housing friction or both..... enough that the FD spring can't overcome it on the low end. That would affect the travel range, which is the main symptom.
    Probably unlikely, but any chance the cage somehow got squeezed so that it's narrower? Another thing to consider is that you have been adjusting things with the "trim click" in place rather than with the shifter fully released for the small chainring. But new cables/casings is likely the first step to a fix. If the new cables don't fix it, you can just keep the old ones for a future replacement since the experiment would confirm that they are still good.

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