>>1834516I rebuilt one the other day because I wanted to change the cup for the axle. Replaced the ball bearings inside. There are 2 races of bearings and the preload is set with spacers so that's simple. Although it does help to have a spare junk freehub to steal spacers from so you can futz with the preload. This is why a lot of freehubs, even on new wheels, have play. It's lazily set.
The whole thing is fiddly work especially trying to hold like a million tiny bears in two races upside down with grease while you assemble it without knocking them but it's not super difficult. Some of the bearing surfaces were pitted but it works quite well now. I suspect most old freehubs are quite pitted, so with new balls and grease they're better than average.
I made the tool to remove the cup by cutting notches into a big socket with a hacksaw and a file. That would be impossible without a vice.
Just soaking the freehub in a container of solvent and flowing oil in past the seal at the back works too.
The most sensible thing if you aren't curious about it and value your time is replacing just the freehub with a new or good used one. If it's shimano they're all pretty interchangeable I think.
