Originally Posted by
invisiblehand
He'd have to get another hub/wheel. The freehub body is different.
He can always measure the space from cog to cog. Shimano 10-speed is 3.95 mm whereas 9-speed is 4.35 mm. I wonder whether the smallest 4 cogs are biased towards 9-speed -- from memory the 9-10-11-13 Capreo cogs are "special" -- whereas the largest are 10. There is usually enough play in the derailer to accommodate some error.
I think the OP's best best is to talk to the cassette manufacturer before doing anything else.
It's a Shimano hub, yes? Is there no other freehub assembly that will slot right in; the Capreo hub takes a proprietary freehub only?
But at that point -- swapping out a freehub -- is getting kind of ridiculous as a means of diagnostics alone.
On the other other hand, depending on what the issue was with the cassette -- if it appeared to be wobbling a bit, out of perpendicular with the axle, I'd strongly suspect the freehub anyway...