More upgrade questions
 

Our tandem is an older mountain style, it has 7 speed set up and I want to upgrade some stuff. I was curious if you could switch out the 7 speed set up to an 8 or even a 9??? I know there can be issues with the space on the back hub but I don't know how limiting this is? The shifters are klunky and I'd like to get rid of them. We really love the bike but its needing some upgrades so we can use it for years to come. I am figuring we will need new cables throughout and maybe new derailleurs too? Fortunately I can get some pretty sweet deals on parts but I'm just hoping I can make an 8 or 9 speed set up work? Anyone have experience with this sort of thing?

What's the rear hub, and what's the spacing on the rear dropout?

A 7 speed hub will not take a 8 speed cassette. An 8/9/10 speed hub will take an 8, 9,or 10 speed cassette.

You may be able to replace the freehub body to upgrade to 8/9/10. But before you did that you'd have to consider the shape of the hub, and the wheel itself.

As Merlin said, you can't do anything until you know the spacing. Late '80s to early '90s, I think that most tandem frames with 7 speed freewheels had 140mm. This, most likely, at least if it is steel, can be cold-set to 145mm, which will open up all kinds of possibilties. 8 to 10 speed hubs will work. I know that a 7 speed derraileur will work up to 9 speed, because I tried it. I believe that 10 speed will not work, because of the different chain used. I think that this might rule out your chainrings for 10 spd, as well. If you are staying with the mountainbike configuration, you can get seperate shifters or the later combo brake /shifters, but then you would need to go with v-brakes (also a nice upgrade if you have cantis); there is a different amount of cable pull. My tandem is road bike, so I found a set of 9 speed bar end shifters.

I took our '94 Trek T-100 from 7 to 8 speed with little difficulty. After replacing the freehub with an 8-10 speed. I recentered the axle then redished the wheel. Along with 8 speed shifters, and even thought it was like new, I also replaced the rear derailure.

BTW, the bike has 140mm rear dropout spacing.

Like another poster, I too was able to upgrade from 7 to 8 speeds with no difficulty. As long as the chain is compatible there is no other issue. I could have gone to 9 speeds if I wanted. My dropout spacing is only 135. All those multi-speed cassettes take up the same amount of spaceb the cogs get thinner as the cog count goes up, but the overall width remains the same. Larger over locknut dimensions (axle spacing) is not so that larger count cassettes will fit but is for the sake of a stronger wheel.

H