what is this and how do I get it off?
 

I have an issue with a freehub on my 1980s vintage racer - the cogs came loose when pedalling and now that I look closer, I think a part may be missing because the rings can now just slide right off. Thought I'd slap on a new cassette since the old one was so worn anyway, but can't find one that fits. It's a shimano sis system, but there's no lockring that I can see, just a some kind of plate with two holes that a pin spanner might fit. I clearly have no clue here. What to do?

Looks like a freewheel to me. You need a freewheel tool to remove and place a new freewheel on it.

It's a freewheel core. Someone removed the cogs. I can vaguely make out 'shimano' on it (?). If that's the case the Park FR-1 tool will get it off.

Re: the title, that's what she said!!

Unless you have a good reason for reusing it, just take a pipe wrench to it after squirting the hub threads with some penetrating oil.

The top cog was threaded and held the others on.

...what they said. If you look at the inside, where the axle comes through, you'll see that it's splined (has notches in it going all the way around). The tool that you need to remove it will look like a large hex nut on one side and have matching splines on the other. You will need to use a considerable amount of force to get that freewheel core off. The best way to do it, if you have access to a bench vise, is to clamp the hex side of the tool in the vise with the splines facing up, place the whole wheel onto the tool so it engages the freewheel core, and turn the wheel counterclockwise until the core breaks loose...

Uh, no... if you clamp the tool in a vise and twist the wheel (for leverage), you still need to turn the wheel counter-clockwise. Whether it's removing the freewheel from the wheel or removing the wheel from the freewheel, it's still lefty-loosey, righty-tighty.

FWIW: it's definitely a Shimano freewheel body. With the correct freewheel tool (Shimano or Park FR-1), it's about the easiest freewheel to remove.

...careful!...remember: threaded freewheels have a 'normal' right-hand thread, so you have to unscrew them counterclockwise, as viewed from the right (drive) side of the wheel, to remove them. So, if you clamp a freewheel remover tool into a vise, the tool becomes stationary and you have to turn the wheel in the opposite direction as you would have to turn the tool. That would be clockwise viewed from the side of the wheel with the tool. Now, when the tool is clamped vertically into the vise, that side of the wheel is facing down. Looking up from the floor, you'd be turning the wheel clockwise. But since you're probably not looking up from the floor when doing this, but looking down onto the left side of the wheel facing up, you're turning the wheel counterclockwise to loosen the freewheel...

...edit: oops...Jeff beat me to it... :lol:

Precisely, my dear Huret...

...why, thank you, Professor Honeydew...

As noted it's just the core of the freewheel with the outer rotatings body, bearings and cogs all gone. Removal with a pipe wrench is a perfectly good approach at this point although the Park or Shimano freewheel puller is a more elegant way to do it.

After it's off, you need a new complete freewheel with however many cogs the old one had. You will also likely need a new chain to match the new freewheel.

Get/borrow a Shimano freewheel removal tool and remove the core. Something like this, with splines for a Shimano Freewheel: http://www.universalcycles.com/shopp...6&category=404. As others have mentioned use a bench vice or something with a long lever arm (be careful to keep the removal tool fully engaged or it will pop out and likely mess up the splines).

6 Speed SIS is hard to come by, but 7 speed stuff seems to be more plentiful. If the freewheel cogs are shot, you'll likely need a new chain too.

I'd get a 7 speed freewheel (not a cassette) and run the shifters in friction mode (non indexed).
http://www.universalcycles.com/shopp...?category=1665

Thanks everyone - I'll have at it this afternoon.

The picture in the OP's post shows a complete freewheel-body without cogs. The outer part will still freewheel in counter-clockwise direction. You need to use a freewheel remover to take it off.

The cassettes that you buy will NOT fit onto this old Shimano freewheel. Why not just slide the cogs back on and hold it all down with the the top threaded-cog?

In order to remove with a pipe wrench, you first have to remove that ring which has holes for a pin spanner. If you are just trying to get rid of the thing, then drive it off with a hammer and cold chisel. It's reverse threaded. After you do that, the rotating part should come right off.

Very good point. OP will need to install the old cogs securely and use a chain whip like this http://www.universalcycles.com/shopp...ls.php?id=1140 to keep the freewheel static while freeing up the core/body.

I think you are right. When I first saw it it I thought was looking at just the core as there seemed to be recesses for the pawls.

Nope, freewheel remover attaches to the centre/core of the freewheel body and it doesn't matter what the outside parts are doing. Chainwhip is only needed to unscrew the top threaded cog in order to change cogs. In this case, I don't know where the cogs are or if they are re-useable.

Ahh, right you are.
It's been a while........ ;)

Shimano tool will probably be useful in the tool box, anyhow ,and is common for other brands ,

get that, and if it doesn't fit, have the bike shop un screw the freewheel core you have,
there are several types on their tool board.

and get the replacement freewheel to fit the tool you have.. which it most likely will .

http://www.loosescrews.com/index.cgi...d=954057031482

http://www.loosescrews.com/index.cgi...d=954057031482

You don't really need a bench vise to remove most freewheels with the proper freewheel tool. All you need is a quick release skewer to retain the tool against the freewheel body splines. Thread the quick release skewer through the small hole on the quick release tool and then on to the hub, engaging the splines FULLY on the inner freewheel body. Get the quick release just snug but not tight like you're mounting a wheel on for riding and "crack" the Freewheel body off the hub by turning the freewheel tool counterclockwise with a BIG adjustable wrench ( I think I use one that has at least a 12" or longer handle). Remove the quick release skewer after you "cracked" it off and continue to unscrew the Freewheel body off with the wrench or sometimes you can just do it by hand by then if the threads on the freewheel and hub happens to be clean and in good condition.

Chombi