Are 6-speed Shimano and Suntour index shifters cross-compatible?
 

A friend just gave me a mid/late 80s Diamondback MTB. Pictures and a real ID/dating thread will come, but for now I'm just trying to get it fixed up. It seems like whoever owned it before my friend took decent care of it, but it's kind of a frankenbike. The bit that bugs me most right now is that the shifters are mismatched and the rear shifter in particular is a crappy plastic friction deal. The rear derailleur is Shimano SIS. I have in my parts bin a decent set of six speed index shifters, period correct, but they are Suntour instead of Shimano. I know not all index systems are compatible, but some are, right? Just hoping to get confirmation on whether this would or would not be expected to work before I get to wrenching.

No.

Shimano Shifters, Shimano RD, Shimano or Suntour FW.

Suntour Shifters, Suntour RD, Shimano or Suntour FW.

Accushift has a different cable pull ratio that's closer to Dura Ace than SIS. (I had Dura Ace 6 speed shifters pulling an XC Comp RD on a 5 speed Suntour Perfect FW that worked. For some reason.)

FWIW, my first foray into Accushift shifters was trying to use a set of 6 speed Command Shifters with an M735 Deore XT RD that looked cool as all get-out. I could get a few cogs to shift nice, but it never indexed across any more than 3 gears in a row. Going through old posts- it looks like you can do 1-2 fine, 2-3 somewhat regularly and after that it's a clown show.

I've heard stories about mixing and matching Accushift and SIS and 7 speed, haven't done it, haven't actually seen it work.

Yellow Jersey has the tech manual:

http://www.yellowjersey.org/sturtech.html

Thanks!

I have a old Klein mtb with Suntour Accushift 7-speed thumbies and a Shimano Deore 6-speed rear derailleur. The shifting works perfectly, but it took some effort. Fortunately for me, the Suntour shifter takes up less cable per pull than the Shimano derailleur requires. I solved the problem by putting a thin piece of metal in the shifter's cable take-up groove. Don't know if this approach would work with your 6-speed shifters but it is worth a try ....you'd just have to experiment with different thicknesses of shim.