Join Date: Dec 2009
Location: Long Island, NY
Bikes: Serotta Legend Ti, Santa Cruz Heckler, Santana Visa TAndem
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.