Ultegra RX rear derailleur 6800 shifter compatibility?
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  1. #1
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    Ultegra RX rear derailleur 6800 shifter compatibility?

    My setup is the Ultegra RX mechanical rear derailleur with the hydraulic 6800 series shifters.

    Is this setup compatible? No matter what I do I can't seem to get it to shift properly. I'm running a SRAM crank with 50/34 rings and an 11-32 6800 cassette.

    Is the B screw adjustment on this derailleur something that has to be exact? The only time I get decent shifting the B screw doesn't have enough tension and the chain goes slack in the 34/11.

    I checked the derailleur hanger and it's fine. Is it possible my chain is too long? When the derailleur is decently tensioned there is half one link between the derailleur top pulley and the bottom of the 32t cog in the 50/32 combo.

  2. #2
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  3. #3
    'brifter' is f'ing stupid
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    Yes they're compatible. I'm guessing the chain is too long. You shouldn't have to screw in a bunch of b-tension to keep the chain from going slack. How did you size the chain?
    Last edited by cxwrench; 1 Week Ago at 05:28 PM.
    #promechaniclife

  4. #4
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    Thanks for the link. So if I'm reading the chart right my shifters (ST-RS685) are compatible with the derailleur (RD-RX800) and the chain (CN-6800). Although some of the pats are highlighted in orange and I'm not quite sure what that means.

  5. #5
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    Quote Originally Posted by cxwrench View Post
    Yes it's they're compatible. I'm guessing the chain is too long. You shouldn't have to screw in a bunch of b-tension to keep the chain from going slack. How did you size the chain?
    I forget if I even did. I may have just taken it off the previous bike using a regular derailleur and smacked it on this. This bike has been in storage for about a year so I haven't really used it. I'll try taking a link out of the chain if I can find an extra pin laying around. Or maybe I'll just install a quick link and call it a day.

  6. #6
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    Quote Originally Posted by cxwrench View Post
    Yes they're compatible. I'm guessing the chain is too long. You shouldn't have to screw in a bunch of b-tension to keep the chain from going slack. How did you size the chain?
    Exactly this. The b-screw being turned out too far should not cause the chain to go slack. It is there to keep the jockey pulley from touching the cassette cogs.

    If your chain is going slack, your chain is too long.
    "If someone needs 200 rolls of toilet paper for a 14-day quarantine, they probably should have made a doctor's appointment way before the COVID-19 outbreak." -- Unknown

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  7. #7
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    Yep, removing one link fixed the issue. Shifting still isn't as great as my road bike but the cable routing is kinda janky and I've been spoiled by my Di2

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