Originally Posted by
roccobike
Sounds like the 6 speed cassette Shimano sold in the late 80s early 90s. While these are not common, replacement parts are not impossible to find. If you have to change it, try replacing it with a early 90's 7 speed freehub and 7 speed cassette and upgrade your shifter. The freehub is bolted onto the hub, I believe its a 10mm hex wrench that is needed to take it off. I've made this change with the exact 6 speed unit you are referring to.
I'm not so sure... The very early Shimano Freehubs did not have a replaceable freehub body. So it would need to be replaced with a Uniglide (I think) cassette.
I had one on my Schwinn Voyaguer, it kept skipping on the rear cog so (blind with rage) I stuck the bike in a trainer, applied the rear brake, and jumped up and down on the pedals, the cog proceeded to disintegrate. I relaced the rim to a Paralax hub I re-spaced to 126mm.