My nine year old Specialised is fitted with the above kit and the indexing is in desperate need of attention this weekend. Trouble is, I can't find the documentation for the bike and I'm struggling to figure out what the little dial on the top of the lever for the rear shifter does. If anyone still has these gears (e.g. museum owners!) please enlighten me! The obvious thing would be cable tension settings, but there are barrel adjusters in the usual places.
The thumbshifter can be set for two modes: friction (infinitely-adjustable) or indexed (click, click). If the thumbscrew on the top of the shifter is backed off a few turns, the cylindrical part below it can be rotated to either friction mode or indexed mode, and the setting is retained by tightening the thumbscrew finger-snug. In friction mode, the tightness of the thumbscrew may affect the stiffness of the shifter's movement as well.
Be aware that it's not easy to find cogs and derailleurs for your ride anymore. One of these days you may need to come to the Dark Side and refit it with Shimano, if you wear out your drivetrain parts.
Thanks for the info, MechBgon. I was reasonably successful getting the indexing back on track this morning (a job made a helluvva lot easier by clamping the bike several inches off the ground with a new Minoura workstand - wish I'd bought one years ago.) Just got in from a quick ride before the light goes and I'd say the gearing is 90%. Bit more to do. Yes, one day the Suntour will have to go. It's a good mech, where did Suntour go so wrong?
Originally posted by dirtbikedude I road with Sun Tour thumb shifters for years. If you want to keep the shifter you can use a Shimano casset but will be limited to using the friction setting on the shifter.
That's true unless they are 8-speed, in which case they should index quite well with 8-speed Shimano.