Originally Posted by Retro Grouch
That's one of those projects that sounds interesting, and you hear about all the time, but I wonder if anybody ever actually does it.
I ran 8-of-9 awhile, basically while waiting for my purchase list to get long enough to merit placing another mail order.(the store with the best deal on shifters and chain didn't carry bodies.)
Most of it worked like a charm. The 9-spd chain played nice with the, by definition, 7-spd chainwheels and both derailers.
I deliberately ignored the first click (which is supposedly bad as the first click pulls a little more cable to take up some slack) in order to avoid pulling the RD against the limit screw in case I overshot the shifting. Worked fine anyhow, although 9-spd is more sensitive to tuning than the old 7-spd was.
When I finally swapped to a 9-spd body I almost went back to the 7-spd. There's a difference in the dustcap and/or axle seal between 7-spd and 9-spd, so there are a few more bits that needs replacing(apart from the body itself) to get the upgraded wheel fully up to spec.
I eventually got hold of a scrapped 9-spd hub that could donate the axle assembly, so I don't rightly remember exactly which parts I swapped out to get the dustcap/axle seal to match.
Best I remember from reading up on this is that Sheldon Brown says that it's enough to replace the axle seal, and that it's available as a spare.
I have a vague recollection of fiddling around with spacers and washers too, but I really can't tell.