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  1. #1
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    Di2 6870 dropping chain and skipped shifts

    I'm having two minor and rare shifting problems. Each occurs less than once per ride.

    1. I'm in the big ring, going downhill, I shift into a smaller cog in the back, and the chain drops onto the small ring. If I soft-pedal, it goes back onto the big ring on its own.

    I'm wondering if I can resolve this with a very minor adjustment of the lateral angle of the FD mech. Do you think the tail might be too far in towards the frame?

    2. I shift into a larger cog in the back, and it overshifts. It goes 2 cogs and then backs down one.

    I know some people have a PERFECT experience with Di2, some need minor adjustments every so often, and others accept this sort of thing as withing the realm of acceptable performance.

    Overall, the drivetrain functions better than any other one I've ridden. I do hilly rides and shift a lot, so perhaps one bad shift per 60 miles is reasonable.

  2. #2
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    Di2 needs to be setup according to the dealers manual which many have referenced here in the past. Make sure your rear hanger is aligned and then follow the manual to the letter. That's all you need to do.

    Sent from my SM-G900W8 using Tapatalk

  3. #3
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    Deleted
    Last edited by TiCoyote; 04-05-2017 at 03:26 AM.

  4. #4
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    Wow. That sounds pretty bad then. I've installed probably 50 di2 systems and alignment plus DM setup is all I've needed for flawless shifting. You didn't mention the support bolt for the front but assume you did if you followed the DM. What frame is this? As well, make sure screws that hold hanger in are torqued and loctite so that hanger is stiff and retains alignment.

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  5. #5
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    This doesn't solve your problem, but I would just confirm what goodboyr says above. What you are describing is not at all a "normal" problem with Di2, or any other current 11sp groupset, which pretty much all shift wonderfully. Either you have some old components in play here (cassette, chain, chainrings) or something went wrong with the install.

    The fact that it is overshifting tells us that something isn't right with the setup. If the hanger really is straight then the RD is not set up right. I don't have as much experience setting up Di2 as goodboyr does, but in the thousands of times I've shifted my multiple di2 bikes, I've never had the RD overshift or even touch one of the other cogs.

  6. #6
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    sounds to me like your high limit on the front DR needs to go outboard a bit more - the only reason it would come off the big ring would be the angle puts the chain up against the FDR pushing it off. Or you have end play in your crank for some reason.
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  7. #7
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    1. I think your hunch sounds correct, I'd for sure at least start there.

    2. Nothing is coming to mind right off.
    use a torque wrench

  8. #8
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    I went back to square-1 and checked out the rear derailleur hangar. It was a little out of alignment, so I straightened it up.

    Before the alignment, when I tuned the rear derailleur with the E-Tube software, the correct setting seemed to be +13. Now, it looks like the setting is +9.

    I also backed off the high-end limit a bit, and I tightened the support bolt, which pushes out the tail of the FD a bit.

    I haven't had a chance to ride it, but I'll keep you updated.

    Thanks for the advice!

  9. #9
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    I started two threads about this, so I'm going to paste this reply in both of them. I hope that is okay.

    I replaced the RD hanger with a Wheels Mfg. The new one is a bit softer and easier to align as others mentioned. It turns out both the original and the Wheels were equally out of alignment, so I'm guessing that they were both straight, but the frame is about out of alignment. I understand that his is common for frames, and straightening the hanger is a good practice when building up a frame.

    Next, I removed the FD and repositioned it. This took a few tries. The best method seemed to be moving the low end adjustment outboard until the outside edge of the cage lined up with the big ring. I also needed to angle the tail of the cage in further than I would expect, and then turn the support bolt a little further than the .5mm that the DM suggests. This means that the support bolt is doing more work, and therefore giving the FD more support.

    At this point, everything was shifting accurately, and the skipped shifts and dropped chains had gone away.

    Finally, I replaced the chain and cassette, which I do every spring anyway, and now everything runs great.

    The only remaining issue is that I get some noise when the chain is cross-geared to the big/big combo. I didn't have that issue before I started this process. Perhaps the FD was out of alignment to the extent that it allowed for cross-chaining, but was causing other interference?

  10. #10
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    Quote Originally Posted by TiCoyote View Post
    I started two threads about this, so I'm going to paste this reply in both of them. I hope that is okay.

    I replaced the RD hanger with a Wheels Mfg. The new one is a bit softer and easier to align as others mentioned. It turns out both the original and the Wheels were equally out of alignment, so I'm guessing that they were both straight, but the frame is about out of alignment. I understand that his is common for frames, and straightening the hanger is a good practice when building up a frame.

    Next, I removed the FD and repositioned it. This took a few tries. The best method seemed to be moving the low end adjustment outboard until the outside edge of the cage lined up with the big ring. I also needed to angle the tail of the cage in further than I would expect, and then turn the support bolt a little further than the .5mm that the DM suggests. This means that the support bolt is doing more work, and therefore giving the FD more support.

    At this point, everything was shifting accurately, and the skipped shifts and dropped chains had gone away.

    Finally, I replaced the chain and cassette, which I do every spring anyway, and now everything runs great.

    The only remaining issue is that I get some noise when the chain is cross-geared to the big/big combo. I didn't have that issue before I started this process. Perhaps the FD was out of alignment to the extent that it allowed for cross-chaining, but was causing other interference?
    Sounds to me like your original problem was a combination of a slightly bent hanger along with a FD that wasn't quite in the right position. And it sounds like you fixed it!

    As for your big/big combo "noise": is the noise the chain rubbing the FD cage, or is it just gear noise (i.e. chain on cogs)? I ask because I find that with a new chain and cassette, using the shimano recommendation for chain length, the big/big combo will often just have a lot of regular "chain noise" compared to others – this is just the extreme angle combined with the large rear cog. If it's chain noise, ignore it.

    If the FD cage is rubbing then there is a micro trim adjustment for the FD; shimano calls it the 'electrical adjustment'.

    It's described in the manual, but it works like this:
    1. Put the bike in the big/big combo.
    2. Press and hold the junction A button to put the bike in adjustment mode.
    3. Use the buttons designed to move the FD so as to micro-adjust (just as you do the RD) the FD so that inner plate of the cage clears the inside of the chain by .5mm.
    4. Press junction A button to take it out of adjustment mode.

  11. #11
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    I've messed around with the FD trim a lot, and I can't seem to get the inner edge that close to the chain. It seems like the cage is just too wide. I'm sure I'm doing something wrong though.

    In answer to your question though, I'm not really sure whether it's regular chain noise or FD rub. It seems to happen on the road but not when the bike is on the stand.

  12. #12
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    Quote Originally Posted by TiCoyote View Post
    I've messed around with the FD trim a lot, and I can't seem to get the inner edge that close to the chain. It seems like the cage is just too wide. I'm sure I'm doing something wrong though.

    In answer to your question though, I'm not really sure whether it's regular chain noise or FD rub. It seems to happen on the road but not when the bike is on the stand.

    This sounds like the FD cage is not parallel and the right height to start with. Either or both of which could cause issues. And/or the fasteners aren't torque to spec.

    BTW you did set the bracing screw with its protective plate on the frame...right?
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