Originally Posted by
70sSanO
I have been swapping older freehub bodies on a few bikes lately. I watched RJ's conversion video, and while I admire his disassembly process, someone just shoot me if I am ever so inclined to to disassemble a freehub body unless it is absolutely the very last resort.
Here is the way I would approach your situation...
I believe the FH-6400 freehub body is a shallow flange (I recently installed a 6401), so you need to find a hub that has a 7 speed Uniglide/Hyperglide freehub body from an FH-MT62, FH-DX-650, FH-1055. The Shimano Part# is Y32E98020. The only caveat is that I have not installed a UG/HG or HG of a FH6400, but I believe the freehub body attach splines are the same.
The one I am talking about is the lower left. The lower right is an 8 speed 6401. Note: The bottom row is shallow flange and the top is a deep flange.
If you get a complete hub, NOS will cost a bit more, you can use the DS cone and it will match the freehub body. Best part of this approach is not having to corral a thousand freehub body ball bearings.
John
I second most of what John says in his post.
Would really not want to totally disassemble a freehub body and deal with the bearings and spacers needed to get a good preload on the bearings. Although, finding a 7 speed freehub body with the correct attachment method is tough now, so this may be the only way.
Many of the older 7 speed freehubs, in addition to those mentioned above, would work, but finding one in good condition is getting difficult. Note that some of the later 7 speeds are Hyperglide only, they no longer had the external threads to use a Uniglide lockring, if that matters.
One correction to John's description of his picture, I believe that the lower right body is from an 8 speed FH-6402 (or similar). The FH-6401 was a 7 speed version that was similar to the bottom left body shown, with threads on both the outside for Uniglide and inside for a Hyperglide lockring.
Swapping in an 8 speed freehub body is possible but note the following:
1. For a 7 speed cassette, a spacer will be needed behind the cassette to move it out enough to get tension on the lockring.
2. The 8 speed freehub body will probably have the position of the bearings further out, so the overlocknut distance will be greater. This will mean that the hub will no longer be 126, more in the 128-129mm range.