Bicycle Mechanics - Do Shimano Sora Shifters work with RX 100 7spd

I have a set of Shimano Sora (8 spd) on a bike that I wrecked and I'm thinking of moving it to my old college era bike - a Trek 1100 with RX 100 derailleurs and 7 speed cassette. They are both designed for triple cranks. Will this work? Do I just have to set the limit screws?

Thanks a lot.

I don't think the rear shifter will work. But you might as well try it!

Alas, it will not. The spacing between the cogs is not much individually but when you multiply it x7, you are going to have some really noisy shifting at either end of the range.

But, check that rear wheel - is that a 7-speed cassette or freewheel? I know that Shimano makes a very inexpensive 8-speed freewheel intended for folks seeking to upgrade to the Sora brifter setup you have. Last one I saw in a shop was only $14. Even an 8-speed cassette can be had cheaply if you hit the web and use a "deal-finder" like Qbike.com to hunt them.

Alas, it will not. The spacing between the cogs is not much individually but when you multiply it x7, you are going to have some really noisy shifting at either end of the range.

But, check that rear wheel - is that a 7-speed cassette or freewheel? I know that Shimano makes a very inexpensive 8-speed freewheel intended for folks seeking to upgrade to the Sora brifter setup you have. Last one I saw in a shop was only $14. Even an 8-speed cassette can be had cheaply if you hit the web and use a "deal-finder" like Qbike.com to hunt them.

8s cassette will generally not fit a 7s cassette freehub body.


Back to the original question. When you set the system up use the middle (4th) cog to set as your "zero offset" position. If you do this then on the largest and smallest cog your "mis-shift" offset will only be 3*0.2mm = 0.6mm

Ah, some cheat sheets that should help you make it work:

http://www.sheldonbrown.com/speeds.html

It will work just fine. Take it from someone who has actually done it. The difference in spacing is not significant.

An 8 speed cassette on a 7 speed hub will not work at all.

See the "Alternate Cable Routing" section http://www.sheldonbrown.com/dura-ace.html#indexing
It says it will work for 10-speed shifters w/9-speed cassette. I wonder if it would help with 8-speed shifter/7-speed cassette?

Check if it is really a 7-speed cassette. If you see a 4.5mm spacer behind the cassette, it should be 8-speed compatible. It's likely 7-speed only, but might as well check.

It will work just fine. Take it from someone who has actually done it. The difference in spacing is not significant.

+1 Okay, I haven't actually done it but I have a friend who has. If your drivetrain is finicky and doesn't shift well, you can replace the 7-speed cassette spacers with 8-speed spacers (with perhaps a 1mm spacer behind it all if needed to snug down the cassette) and, voila, you have 8-speed spacing on your 7-speed cassette.

Thanks for the help and ideas.

I also have an 8 spd cassette from the wrecked bike that could be used to help solve this problem. Does that add any additional/better solutions?

Thanks.

I know that Shimano makes a very inexpensive 8-speed freewheel intended for folks seeking to upgrade to the Sora brifter setup you have. Last one I saw in a shop was only $14.
Shimano still makes a couple of 7-speed freewheels but I don't think they ever made 8-speed freewheels.

There are 8-speed freewheels available from Sun Race and these are quite cheap but problematic as the excess length makes them even more prone to causing broken axles then even 7 or 6-speed freewheels. Also, an 8-speed freewheel requires a 130 mm OLD hub and dropout width just like an 8-speed cassette hub.

I have done Shedon Brown's alternate routing to make an 8 sp Sora shifter work with a 7sp cassette. However after 6 months the rim failed so I bought a new wheel with 8 sp hub.

If you can't "transplant" the entire wheel from the wrecked bike, you would have to transplant the free hub BODY along with the 8 speed cassette. The 7 speed body is too short for an 8 speed cassette.
Gonzo Bob's idea should also work. You do have the spacers on the 8 speed cassette you could steel.
If it were me, I'd probably pick the method that gave me the most useful gears for my needs.

No alternate cable routing is needed to run 8 speed shifters with a 7 speed cassette or freewheel. If you don't believe me, read Sheldon Brown, or better yet, try it yourself.

Thanks for the help and ideas.

I also have an 8 spd cassette from the wrecked bike that could be used to help solve this problem. Does that add any additional/better solutions?

Thanks.

That's the route that I would try. Take off the biggest cog. You might have to grind off the rivets. That'll give you a cassette that has 8-speed spacing but will fit the 7-speed freehub body.

FWIW I've fiddled many times with mixing and matching 7 and 8-speed parts. I can get it to "kind of" work but never to my satisfaction. I guess that means that either I'm pickier than those other guys or a less adept mechanic.