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  1. #1
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    Mid cage 7800 derailleur on an 11 speed system

    I've got a near-new Dura Ace 7800 in my parts stash, bought many years ago. Call it advance planning for the day my 50/34 by 11-28 would not cut it for me (on my climbing bike). Want to stay 50/34 (do not want to go triple!) and mate with something like an 11-32 (or 34) cassette.

    Will the 7800's 10sp jockey wheels work okay? Or does this call for slapping some of the thinner 11sp pulleys on there? The other option is to just buy an Ultegra mid cage for under $100. Not sure if anybody else here attempted any of this; my topic search did not unearth anything. Thank you in advance for opinions or advice.

  2. #2
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    A 7800 derailleur won’t be able to be used with a 32t or 34t large cog. The design of that derailleur won’t allow the upper pulley won’t clear those large cogs.
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  3. #3
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    Quote Originally Posted by DaveT View Post
    A 7800 derailleur won’t be able to be used with a 32t or 34t large cog. The design of that derailleur won’t allow the upper pulley won’t clear those large cogs.
    On top of what Dave said, the 7800 is a 10-speed derailleur. It will not work with an 11-speed shifter as Shimano changed the pull ratios on their road drive trains when they went from 10-speed to 11-speed.
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  4. #4
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    Yeah, that's not gonna work at all. You should check the spec on that derailleur and you'll understand. Maybe.
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  5. #5
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    Quote Originally Posted by fast ferd View Post
    Will the 7800's 10sp jockey wheels work okay? Or does this call for slapping some of the thinner 11sp pulleys on there?
    I know you're not really asking about just jockey wheels like the wording implies, but the top pulley on 7800 has quite a bit of float. 11 speed top pulley does not. So there's that too on top of what others said.

  6. #6
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    Quote Originally Posted by cxwrench View Post
    Yeah, that's not gonna work at all. You should check the spec on that derailleur and you'll understand. Maybe.
    As far as it not working with larger cogged cassettes, won't that depend whether it's SS (short cage) or GS (mid-cage)? GS will work up to a 32T cassette on a compact double crankset, only 30T on a triple.

    But no, it won't work for all the other reasons mentioned in this thread. Buy the correct RD for the job. 105 and Ultegra are inexpensive enough and 10-speed mid-cage derailleurs are still plentiful.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  7. #7
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    Thank you for the feedback. I looked at the 9100 - for the first time just now - and it utilizes a longer cage than the 9000. It accepts up to 30t cogs and a 35t differential. Betting a 32t cog will work fine. Plus, I rarely go small/small or big/big. Hoping to find one for a decent price. Maybe eBay my GS 7800 to offset the cost. Bit of a Dura Ace snob here.
    Last edited by fast ferd; 12-22-2017 at 09:26 AM.

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