gate28

Downtube indexed shifters. Bike didn't come with the proper back wheel.
I have a 7 speed cassette. My bike requires a 6 speed only. Can I turn/ use the 7 speed cassette and leave off a sprocket to make it 6 only?
Thanks.

dabac

While keeping the indexing - probably not.
Best I can remember, 6-speed uses a 5.50 mm gap between sprockets while 7-speed use 5.00 mm spacing.
If you adjust the derailer to run clean in the middle of the cassette, you’ll be 1-1.5 mm off at the ends.
6-speed freewheels are still available and work OK. Get a wheel that’ll take one of those or run your shifter in friction.

blamester

Make sure it is 6 speed first. 6 clicks on the shifter means it is 7speed.
If the 7 speed wheel fits then use it as it is in friction mode.On a modern cassette it's surprisingly easy.
Shifters are out there if you need them 7/8/9 and 10 speed.

Bike Gremlin

As far as shifting goes - 7 speed cassettes have sprockets aligned at 5 mm.
6 speed ones are either 5 mm, or 5.5. If your shifters are 6 speed ones for 5.5 cassettes, they won't work with a 7 speed cassete.

For fitting a 7 speed cassette onto a (free)hub and into a frame I'd need to ask a few more questions:

Spacing between the rear dropouts: 120, 126, 130, or 135 mm?

What is the OLD of the rear hub you plan to use?
Is it a freewheel, or a freehub hub?

maddog34

6 speed rear gear sets have never been a "cassette"... they are all FREEWHEELS. the ratchet mechanism is part of the gear cluster... 7 speed clusters can be either a freewheel type(common on box store bikes) or a cassette type, mounted on a FREEHUB type hub.

the "hyperglide" gear clusters may be either a freehub OR freewheel design...
freewheel type... https://www.ebay.com/itm/New-Shimano...0AAOSw5VFWIEYz

freehub type... https://www.ebay.com/itm/Shimano-Cas...YAAOSwUYNaOslJ

Note the RETAINING RING on the freehub type? that is an external piece that holds the gears on the freehub ratchet body...

Note on the freeWHEEL gear cluster how the center area is inset, not external...

Which rear gear cluster does your bike have on it now?

ThermionicScott 

Totally wrong! The Shimano cassette freehub was introduced in 5- and 6-speed models in ~1978, long before there was a 7-speed model.

fixedweasel

Quite so Therm albeit to covet is as likely to obtaining Hen's Teeth

Kontact 

Often the least expensive wheel/cogset combination is a threaded hub with a freewheel. 6 speed freewheels are plentiful and cheap, as are 7 speed freewheels. But there are used Uniglide 6 speed freehub wheels out there on Craigslist that might be cheap enough to be worthwhile.

If you have any doubts about the shifter, post the model number. It is usually stamped or printed on the shifter body.

ThermionicScott 

Yeah, but every so often we'll get a new poster asking about a wheel that turns out to be one. Kind of neat when that happens.

maddog34

ahhhh... the short-lived, specific to that hub only, Dura-ace ?

never seen one in person.

i do recall some collector hunting for one on another forum though.... damn rare now... damn rare then, too.... an ancient DA hubbed wheel popped up recently on PDX CL... $30, no cassette though, and the seller mentioned the oddball splines on the freehub... so it's basically useless.

not really relevant to this thread, but history is good, i guess.

uniglide were almost all 7 speed, from what i've seen. there were a very few 6 speed ones... the resto-freaks tend to hoard them.

kinda doubt the OP has the ancient DA, or a Uniglide.... still waiting on more info.... i'm leaning toward freewheel.

ThermionicScott 

Not really. Dura-Ace and 600 from 1978 for about a decade, (A)105 from its introduction in 1983 to 1990. Practically an eternity compared to some of Shimano's other offerings.

What you've personally seen (or not) isn't relevant to this thread, either. My point is that it was out there for quite a while, and BF posters do find themselves in possession of it from time to time.

That said, it is more likely for the OP to have a regular freewheel. Maybe he'll return and share more info.

dedhed

I dunno, I have 2 bikes waiting for me to get around to that have them on. FH-R105

BillyD

Alright, both you guys leave this thread. Kontact and Maddog34, do not post further in this thread. Warning.

gate28

That's very helpful. Thankyou. Can you switch downtube shifters from index to friction?

gate28

Yes it is 6. I was thinking I'd just take a sprocket of a 7 speed cassette. I'd like to keep the shifters original.
I just need to find an old wheel with a 6 speed cassette on it. Thanks.

gate28

It came with completely the wrong rear wheel. That's now in the bin. I have at the moment a set of Rims with a 7 speed Shimano ultegra freehub arrangement that I would like to use. I was wondering if I took out a small sprocket would it still work with the 6 speed shifters.

ThermionicScott 

Look at the side of the shifter and see if it has markings for "friction" and "index" (SIS in the case of Shimano shifters), with some kind of rotating ring to select one. See my avatar.

If they are index-only, then you won't be able to use a 7-speed freewheel or cassette, even if you do remove one cog. The spacing is all wrong between 6- and 7-speed, as posted by several before me. I've tried it.

dabac

Uni-glide came in 6-speed too.
My first drop bar bike, a Chimo, has one.

They’re rare, but nor horribly so.

dabac

There are two things here:
-what will physically fit
-what will shift as intended

Simply taking out a sprocket won’t work. The smallest sprocket usually has the spacer integrated, and removing that will give you a too short stack to be clamped by the lockring.
You’ll likely need to add a spacer to get it to clamp properly.
Taking out the biggest sprocket but leaving the spacer might mount up OK.

Then there’s indexing. Sometimes it’s possible to change the amount of derailer movement by clamping the cable in another way. Or by adding an adapter (see shiftmate).
Sometimes it’s possible to take the spacers from a worn out cassette with the desired speeds/spacing and use them with the sprockets from another cassette to get a spacing close enough to index right.

gate28

Bingo. I've switched the shifters to 'Friction'. Easy. Thanks.

GrainBrain

There's a guy in the classic and vintage forum selling a ton of old Suntour 7 speed shifter handles. Would one of these work in getting indexing back? I'm not sure, and friction shifting is probably fine just had to laugh at how many he has!

https://www.bikeforums.net/classic-v...leur-only.html