johnspack

Have a late 80s mtb that's all shimano. Has 126mm dropout, I shouldn't have an issue replacing my 6 speed with a 7 right? I have to pull my freewheel apart anyways, so might as well.

hermanchauw

1. What are you trying to achieve by going 7 speed?

2.. Are you planning to use the same wheel with 7 speed freewheel?

3. Is your frame steel?

mixteup

Should be OK :

Freewheels (Thread on Type) for Bicycles from Harris Cyclery

HillRider

Both 6 and 7-speed freewheel and cassette hubs are 126 mm OLD so your current wheel and frame should accept the 7-speed freewheel with no difficulty. If you have 6-speed indexed shifting, it won't work with the 7-speed but if you have friction shifting it will be fine but you will probably have to adjust the rear derailleur's limit screws a bit.

clengman

My situation may be unique or it might be different going from 6 speed to 7 speed, but I recently replaced a 5 speed freewheel with a 7 speed, and I had to add spacers to the drive side and redish to make enough room for the new freewheel. It wasn't that big a deal, but it wasn't as easy as I had hoped it would be.

andrewclaus

I just tried it in the non-profit shop the other day, and it didn't work. It looked fine until the chain went on, with no clearance to the seat stay. The solution the post above was too involved for the bike and the volunteer mechanics involved.

Andrew R Stewart 

The replies give the range of likely results. The FW will thread onto the hub well enough, it will likely clear the frame when the wheel is installed and the chain might even clear the stay ends too. But just as likely is that the chain will contact the seat stay end, if not when running on the small cog then maybe when it lifts up as it shifts off and climbs onto that next cog. This can cause the chain to jam and stop moving, not good if you're not expecting it.

What will really be the case is dependent on the dimension of the freewheel width, the axle end nut to freewheel seat on the shell and the frame's stay ends (how far down to the slot is it and how far to the inside the stay's 'thickness" extends). That's a lot of variables to anticipate fully, even for an experienced guy.

So once again the best answer is maybe why don't you try it and report back. Andy

HillRider

5-speed freewheel hubs were typically spaced 120 mm so substituting a 7-speed, requiring a 126 mm hub, is not straightforward.

Andy is correct that a 7-speed freewheel is slightly wider than a 6-speed, even thought the nominal hub width is the same. So, respacing the axle with a thin spacer on the drive side may be needed to get chain clearance.

3alarmer 

...+1. What's the point ? You can get the same overall range with a six and your chances of running into the above issues are zero.
Plus you can still use your indexing, which is an advantage on a mountain bike. Assuming you are using it as such.

nfmisso

Just to add to Andy's comments: different 7 speed freewheels have different overall widths, even though the cog to cog spacing is the same. Just more variables to deal with.

WizardOfBoz

Andrew,
Excellent, cogent reply. Upped my knowledge - thanks!

Gratuititous joke warning - completely off topic (the used of the word "upped" triggered this):
As an aside, you may be amused to recall a humorous slogan used by Pat Paulsen. Paulsen was a comedian who gained great notoriety for his roles on the Smothers Brother's show. He played a deadpan milquetoast fellow (in reality, he was pretty tough - he'd been US Marine who served just as WW II was ending). Anyway, he declared his candidacy for presidency, and his compaign speeches were hilarious and clever- he really parodied those in power. His campaign slogan is the point here: "We're raising our standards. Up yours!".

I also recall him talking about Hawaii and informing folks that a wahine was something you served on a bu-hun with mu-hustard. Ah, the good old days.

clengman

My dropouts are 126mm, but I suspect the hub was indeed 120mm OLD. After I added spacers, I had to buy a longer axle.

fietsbob

all the 7 speeds I've seen, the added cog is in the middle , High gear still a 13t..
screwing onto the Freewheel body.

the spacers between the cogs got thinner and as a result the chains had to be thinner as well

overall width close to same, add a little shim spacer on axle if not clearing frame ..



...

70sSanO

Andrew R Stewart 

Since the Op never said what he was trying to achieve we don't know if the 7 speed freewheel might have a different ratio range, or he's looking for tighter gaps between shifts. both are worthy goals. Andy

johnspack

Well I looked at the 7 speed specs and there is an extra gear in the middle some where. I assume that will give me smoother shifting from high to low. It uses friction shifting, and has a steel frame. I'm slowly restoring the bike for fun.
Couldn't even ride it at first, but now riding many miles a day on it. If I'm going to pull the freewheel anyways, figured a nice new 7 speed in there would be nice! I don't think a different chain is required for going from 6 to 7, but I don't
mind replacing that anyways. It's just a silly project that I now can't stop.....

3alarmer 

...speaking generally, this is not true. If you want "smoother" shifting, look for a 6 speed freewheel with ramped teeth as your replacement, and buy yourself a KMC 8.93 chain for 12 bucks. Use plastic lined cable housing, and if you want the deluxe version, buy die drawn (smooth) stainless steel cables for your derailleurs. If you are using used but still functional parts, look for an old Shimano 6 speed freewheel with the teeth on the cogs slightly twisted to assist in chain pickup. Suntour did a similar thing by grinding the teeth so they were a little high on the pickup side.

I would caution you against buying a used freewheel off e-bay or similar sites. They often have one cog (often in the 18 or 16 range) that got used a lot more than the others and is worn. You cana repplace cogs if you have a source, but they are getting harder to find unless you rob other freewheels. nttawwt

johnspack

Was actually looking at 7 speeds with ramped teeth. I believe I can get a brand new one. Not buying from ebay, only accredited online bike shops. My local bike shop may actually have one. And yes, might as well replace my chain as well. And nice idea on cable housings,
hadn't really though of that. Will replace now. Yes, old bike is going to cost me a bit to get right....

ddeand 

johnspack

Yes, I'm prepared to add a spacer if that is needed. Also think I want a new derailleur and chain to go with it. Whatever makes shifting from high to low on a hill easier.