old Shimano 6 speed cassette
 

The GF has a 20+ year old Univega mtb that is heavy and beat. But she has pedaled around Ireland, San Fransisco and NYC on it and is quite attached to it. The chain started jumping teeth lately until finally it broke. Everything is original so I figured I'd replace the cassette and chain. Not so fast! The Park lock ring tool I have doesn't fit, even though it looks like it should. I took a look at Sheldon Brown's site and it looks like I have a threaded on small sprocket, probably a Uniglide hub. I have not yet been able to budge it to get it off. Tried heat and penetrating oil and two pieces of chain with vice grips. Before I bring it to my LBS, what else can I do? I don't want to spend $$ on this old clunker. At first I figured I could score a $15 cassette at Nashbar and I'd be good. Now I see that isn't so easy with a 6 speed. What to do?

You have a freeWHEEL. The tool you need looks like your lockring tool with longer splines. Insert the tool, put the axle nut or skewer back in to secure the tool, clamp the tool in a vise, and grabbing the tire, take a big left turn in the bus.

If it's been on there 20 years, some cussing may be required.

buy urself a can of PB blaster if that freewheel is seized on. let it soak... that stuff does flippin wonders. get the right tool park tool # fr-7 i believe and have at it

yes, but what about replacing the 6 speed cassette?

You just need to buy a six speed freewheel (not cassette), actually Nashbar has those too now that I look. You generally can fit a seven speed on there, but that will cause problems if you have index shifting. If it is friction shifting then either a six or seven speed freewheel should work.

There were some 6-speed cassettes, I would not assume that it is a freewheel just because it is a 6-speed.

If the OP can see some splines ("lock ring tool doesn't fit, even though it looks like it should") he's got a freewheel.

I'm a little confused, but I think it's getting clearer. I was trying to remove the smallest sprocket that is threaded on, but if I must replace the freewheel anyway is this even necessary? Should I be able to thread a new freewheel on there and be good? Are they standard? Maybe pay my LBS to remove the old one rather than buy a tool I will only use once. Thanks for the help guys.

If the freewheel itself isn't in bad shape then no it wouldn't have to be replaced. I have the same thing on my bike. I had to go to New-Old-Stock on ebay. I got one for about 60 bux. Then i replaced the chainrings, the chain and basically the whole drive train.

Shimano-compatible freewheel tool and cassette lockring tool look similar, but are not the same. It wouldn't be a bad idea to buy the freewheel remover because you'll need it if you ever want to remove your new freewheel (but you don't need it to install a freewheel). But, you could just pay the LBS to remove the old one and the next one down the road because in all likelihood the next one won't be needing removal till it's time for a new one.

LBS charged me $3 to remove it. He had to put in in the big vice and really crank on it, so I never would have gotten it off. Just ordered a $22 6 speed freewheel from Nashbar, and an $11 chain, so I'm back in business after I repack the bearings. Thanks guys.