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  1. #1
    your god hates me
    Reputation: Bob Ross's Avatar
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    Help! RD won't take up chain slack!

    This problem just started appearing with my 7-year-old Ultegra 6700 rear derailler:

    The entire RD assembly no longer swings all the way rearward to take up the chain slack when I shift towards smaller cogs.

    It seems to be most prevalent when I'm in the small chainring, to the point where I can't use the 5 smallest cogs or the chain goes too slack to shift and often too slack to engage the drivetrain & propel the bike forward reliably.

    It's less of an issue when I'm in the big chainring, but still causes skipping and misshifting in those smaller cogs.

    Thinking the problem might be dirt/gunk impeding the return spring -- I'm just presuming there is a "return spring" that controls this aspect of an RD's function, hell if I know -- I removed the RD from the bike and gave it a good soaking/cleaning with Simple Green, followed by a liberal dousing with WD-40. That seemed to cure the misbehavior for one or two rides, but now it's happening again.

    So...what's going on, and what's the cure?

    Looking at an exploded parts view here I gather that coily spring that's part of the "B-Axle Assembly" could be the culprit? Is that something my LBS can easily replace? Is that something I can buy at my LBS and replace myself? Is there some other part or sub-assembly that's more likely the culprit? Or is my entire RD shot, in need of replacement?

    Thanks.

  2. #2
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    You probably just need to take the derailleur apart (the b-axle stuff) and clean it thoroughly, lube it, and put it back on the bike. I've seen this same problem many times and it's rare the derailleur needs to be replaced. Remove the clip and take it apart, it's very easy.
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  3. #3
    RoadBikeReview Member
    Reputation: No Time Toulouse's Avatar
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    Also, you may have tightened the mounting bolt too much.
    I'm upping my standards;
    Up yours!

  4. #4
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    Reputation: MR_GRUMPY's Avatar
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    Possible internal broken spring???? I had a C-Record derailleur that did that.....Try all the other cures first before giving up.
    If your opinion differs from mine, ..........Too bad.
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  5. #5
    Forever a Student
    Reputation: MMsRepBike's Avatar
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    use a torque wrench

  6. #6
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    use a torque wrench

  7. #7
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    Quote Originally Posted by No Time Toulouse View Post
    Also, you may have tightened the mounting bolt too much.
    Seriously? That's not possible.
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  8. #8
    RoadBikeReview Member
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    If you haven't disassembled the derailleur and cleaned it up, then I'd say the spring is toast.

    Happened to me and a Shimano Deore derailleur. One day it was fine, the next...

    Help!  RD won't take up chain slack!-derailleur1.jpg

  9. #9
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    Reputation: velodog's Avatar
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    The only thing that I can suggest is to just lean that bike against a wall and ride your Sachs.
    Too old to ride plastic

  10. #10
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    Quote Originally Posted by Bob Ross View Post
    Looking at an exploded parts view here I gather that coily spring that's part of the "B-Axle Assembly" could be the culprit? Is that something my LBS can easily replace? Is that something I can buy at my LBS and replace myself? Is there some other part or sub-assembly that's more likely the culprit? Or is my entire RD shot, in need of replacement?

    Thanks.
    https://www.modernbike.com/shimano-d...-axle-assembly

  11. #11
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    Quote Originally Posted by MR_GRUMPY View Post
    Possible internal broken spring????
    If that spring broke then the idler cage would just be hanging loose - not taking up any chain at all. cwrench has the right answer: take it apart, clean it, lube it. In that process the OP will find if something is bent/broken.

  12. #12
    RoadBikeReview Member
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    All I have to add is WD-40 is not a proper lubricant. Great for cleaning things but not for chains, pulleys, etc.

  13. #13
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    Quote Originally Posted by loxx0050 View Post
    All I have to add is WD-40 is not a proper lubricant. Great for cleaning things but not for chains, pulleys, etc.
    Didn't intend to use it as lube, point was to use a water displacer after the Simple Green soak.

  14. #14
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    Quote Originally Posted by Bob Ross View Post
    Didn't intend to use it as lube, point was to use a water displacer after the Simple Green soak.
    Don't worry, there is enough oil in WD to work ok on most things as a lubricant. People have been doing it for decades and not had any problems. It's not like it's devoid of oil...it's certainly better than nothing.
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  15. #15
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    There seem to be a few misconceptions about WD-40. I had the same misconception about WD-40 being a great water displacer and parts freer, but lousy lubricant. Our very own Mike T. here on RBR set me straight in a thread on one of our favorite beaten to death topics - chain lube! You can check it out on Wikipedia. Their formula is somewhat of a trade secret, but it's pretty much a mix of mineral spirits and petro based oil. See below and scroll down to Mike's posts:

    https://tinyurl.com/yd7vtkj8
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