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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

  • I don't think I'd expect Deore XT and Ultegra to be compatible, one is MTB and the other is road – Vorsprung Oct 5 '16 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 Oct 6 '16 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 Oct 6 '16 at 9:15
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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 Jan 23 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 Jan 24 at 13:14

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