6 gear shifter 7 gear cassette
 

forgive me for my knowldge of gear stuff is limited, until now ive ridden bmx>singlespeed>3 speed hub>fixed.

im putting togather a geared beater roadbike for my commute to work. the frame, wheels, and rear derailleur+shifter are from seperate bikes, so its a bit of a frankenstein.



the rear cassette has 7 gears and one front 52t and im just using a rear derailleur. the problem is that the shifter+derailior come from a bike with 6 gears, so the indexed shifter does not mesh with the diffrent 7 gear cassette.

The derailleurs reach is fine and i have set the H + L to be perfect, however im not sure how im going to use the shifter.


can i set it up so that i only use 6 gears of the 7 on the cassette?
should i skip the index and just use friction shift?
get a new shifter? (dont want to spend much, last resort)
any other ideas?

thanks for your time

Get a new shifter. The old one won't work well at all with a 7-spd cassette.
A cheap SRAM shifter shouldn't cost you more than $10.

There are some 6 speed shifters that will work with a particular 7 speed rear, but they are in the minority -need more specifics.

If this were say Shimano, 6 speed SIS uses 5.3 mm between cogs-Center to Center, vs. 7 speed using 5.0 mm Center to Center.

If this is Shimano SIS on the rear cogset and shifter, your best bet if you don't change the shifter would be to get the center cog lined up with the 4 shifter positio, then hope the .9 mm difference extreme is not too much difference to cause the chain to skip.

You'll have better luck if you have downtube and stem shifters than grip or triggers as you can run them as friction shifters between the 2 smallest cogs.

If you have a friction/index switch on the shifter, you may find friction mode works better-or you could use indexed mode near the middle cogs and flip to indexed as you get away from the middle cog. I have had stem, downtube, and trigger 6 speed shifters that had an index/friction switch.

Or you could just run full time in friction mode.

I once tried to get a French freewheel with 5.1 mm center-center spacing to work on Shimano SIS-6 with no luck, so sometimes you have to toss in the towel. Maybe that would have worked with 7 speed SIS.

If you have mixed brands and different shifting standards, that sometimes makes it harder, sometimes easier.

ill take accurate measurments tommorow.

my shifter is a late 80s top mount thumb shifter, with a lever to select friction/indexed.


the other small problem i have is, i dont know where the best place to put the shifter on my drop handlebars, i cant seem to find a comfortable position.

Any chance you have the freewheel that the 6S shifter was originally used with or the shifter that your 7S freewheel was with? I`m guessing you wouldn`t be writing here if you did, but ya never know- that would be the cheapest fix.

both the new and old cassettes are shimano, and have 5.5 spacing. however the old one is a mtb and the new a road bike.

i have the old freewheel but it wont fit the new road hubs im using.

the bike origionally had downtube friction shifters, but these are screwed from the previous owner/s. i found the bike in a skip but i love riding it, but im tired of running it 52-17 ss, well to heavy for commuting 25m 4 times a day.



im thinking ill set the H reach to miss the lowest gear on the casette so im effectivly using 6 of the 7 gears and still use the indexing. is this going to work?


if i decide to keep all 7 gears and just use friction shifting, is the derailleur going to cross the gears smoothly in the right increments?


ive yet to actually put it all together and test it, as i need to braze on a cable guide as the bike was designed for downtube shifters. so for the moment were talking about how it would work theoretically.

Just remember there is other ways to do this than to braze it on. Is there a mount brased on the frame for the downtube shifters? If so, you could use the downtube cable stops http://www.velo-orange.com/deandsh.html

Also if you`we got the clamp on thing from the downtube shifter the prew owner messed up maybe you can use the cablestop on that clamp?

Unless you`we got the brazing stuff at home and do it all the time..

Sure you can buy some clamp-on stops also. I`we got them, but hard to explain. Find a good bikeshop and ask.

I put a 6 cogs rear wheel on a bike with a 7 shifter today. Not sure how it works, but it is only for my son to use when I put studded tyres on his MTB. Are going to rebuild some wheels for it.

nah, i threw the old shifters out cause they were completely screwed, and they were the clamp type so there is no mounts on the frame.

i could use a clamp, but i would have to find them, buy them, and wait for them to arrive. its easier for me to just braze them myself when i get the time, and a more elegant and reliable solution.


if i get the time i might bodge the whole thing togather with some jubilee clips and see how well it works.

I'd just use friction mode if you have it. IF you decide you want indexed, you could always do that at a later time.
I've gone to 8 speed from 7 with the same shifters without problem. I could go even more if I wasn't too cheap to buy the new chain required!
Friction is less trouble to keep adjusted and with a bit of practice, your shifts will be just fine!

thumb shifter
 

Run it in friction, and mount it on the bottom of the drops, like it was a bar end shifter. I ran a bike like this for a while and it worked great. The only issue I remember was the rear shifter had to sit on the left for the lever to move in the right direction. It got confusing switching between bikes with bar ends that work in opposite directions.

well i bodged it togather to see how it would work.
the indexing just wouldnt work. either the top three would change well and the bottom wouldnt, or vice versa. i could get them to change down, but not up, or vice versa.

it worked really well in friction mode, but im concerned about how easy this type of shifting is to use. ill give a whirl. the pull upon the trigger is really quite tough though.

Could you be more specific on your shifter and derailleur?

This link has spacing info:
http://www.sheldonbrown.com/cribsheet-spacing.html

If those are Shimano 6 & 7 speed cassettes, the spacing should be 5.3 and 5.0 mm respectively.