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After remaining unchanged (with a few exceptions like FH-7801) for nearly 20 years the Shimano freehub body spline mount has changed along with the width. I had hoped I could refit a 8/9/10 speed rear hub (FH-M756) to work with 11 speed. But the mounting face on the 11 speed freehub body is totally different compared to the old 8/9/10 design. I don't see any hope in retrofitting old hubs with new freehub bodies. Anyone found a solution short of hub / wheel replacement? The "Zinn" filing down method seems to be the only hack available for standard Shimano brand hubs.

FH-M756 freehub body Y3BD98010 cannot be replaced with FH-6800 body Y3CZ12000 (see photo).

Freehub body mount comparison

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  • I don't think I'd expect Deore XT and Ultegra to be compatible, one is MTB and the other is road
    – Vorsprung
    Commented Oct 5, 2016 at 20:02
  • @Vorsprung Many Shimano freehub bodies for hubs with standard M10 axles attach using the same interface on the hub shell without regard to being mountain or road, and many (not all) are dimensionally very similar. This gives rise to many instances where freehub bodies may be cross-compatible in the sense of being adaptable with some tweaking of dish, axle spacing, transplanting cones, etc. It's true that they usually won't be compatible in the sense of being drop-in replacements.
    – Nathan Knutson
    Commented Oct 6, 2016 at 6:00

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There is no remotely practical way of doing it. It's possible that could change in the future as 11 trickles down more, but probably not likely given that the interface is also different on the standard axle, less expensive 11-speed road hubs they've already made.

Just to be clear though, 11-speed MTB cassettes do not require a new longer freehub, because the large cog overhangs.

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    The 11 speed Ultegra pictured is required for the wider 11 speed road cassettes but not for the new crazy 40 tooth 11 speed MTB cassettes. Seems a shame that Shimano are breaking compatibility in several places across their range
    – Vorsprung
    Commented Oct 6, 2016 at 9:15
  • At the time of writing, Shimano’s HG700 and HG800 11-34 cassettes didn’t exist. However, they do now, and they fit on 10s and earlier freehubs because the last cog is cantilevered over the hub flange as with MTB cassettes. They’re an option for road riders, whereas the MTB cassettes might be too big for many rear derailers.
    – Weiwen Ng
    Commented Dec 12, 2020 at 12:21
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I just put an 11-speed SRAM cassette (11-42) on a Shimano FH-M756 (xt 9/10 speed rear hub), and it works just fine. as mentioned above.

Cassette large cog is 42 tooth so it overhangs, and the cassette uses the 10 speed freehub body size.

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Why would you need or want to swap the freehubs? Can you not put a spacer inboard to fit 8/9/10 speed cassettes, like you can to fit a 7 speed cassette on an 8/9/10 speed freehub?

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    Good thought, but OP wants to put an 11 speed cassette on a wheel that is currently 8/9/10 speed, and the freehub body is too narrow, not too wide.
    – Criggie ♦
    Commented Jan 23, 2020 at 6:24
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    Oops sorry! So yes not possible with Shimano 8/9/10 speed hubs, as explained here, with a useful chart part way down: slowtwitch.com/Tech/Cassette_How-To_-_Part_2_3257.html
    – Nigel Andrews
    Commented Jan 24, 2020 at 13:14
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My Sram 11 speed PG-1170 fits perfectly on my Shimano FH-6400, the only problem is that the thread on the lock ring is too short and doesn't reach the hub; I think I will get somebody to make me a custom lock ring.

P.S. the Shimano FH-6400 tricolor was the most beautiful hub Shimano ever made!👌

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  • Hi, welcome to bicycles. Since the question isn't about a FH-6400, I'm not sure how this helps. Please make sure that you actually answer the question being asked.
    – DavidW
    Commented Dec 11, 2020 at 21:10
  • @DavidW actually, you could read the answer as “put an SRAM PG1170 cassette on the hub,” which is an answer, but if the lockring doesn’t thread in properly it’s potentially a wrong answer. I suspect the cassette’s total height exceeds the height of the freehub body. For reference, the poster is referring to an 8s Ultegra hub.
    – Weiwen Ng
    Commented Dec 12, 2020 at 11:59

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