So, way back in the day, when the Buffmeister was almost a young man, he worked as a mechanic. Riders would come in with bikes that they'd crashed, and often the casualty was a broken thumb-shifter. They usually broke at the weakest point, which is at the end of the plastic grip that one pushes with their thumb. Some people would have damage to the plastic cap that covers the internals, Shimano did sell replacement caps, but there were many varieties, two different "hands" of them, and few stores carried that part. Shimano only sold thumb-shifters in pairs, of course, and so customers would "donate" one perfectly good, and one broken thumb-shifter to me after replacing both. Pretty soon I had a small box of broken shifters, and I figured out a way of repairing them.
Here's the method I devised.
1...Where the shifter usually broke, flatten the aluminum square with a flat file.
2...Drill a blind hole into the remaining peg, not so far as you drill into the internals and totally bugger the shifter ;-(
3...Screw in a sheet metal screw of sufficient length that when fully in you have about one inch sticking out the thumb-shifter. Screw it in with permanent locktite or 5 minute epoxy on the threads.
4...Wait for it to set. Cut off the head of the screw. grind a point where the head was.
5...Drill a piece of dowel or exotic wood with a blind hole.
6...Fill the hole with epoxy and screw the dowel tightly on the screw. Fill all cracks, imperfections with epoxy.
7...Let it set, overnight.
8...Sand the dowel to shape, decorate/embellish to your liking. In the pic, mine are decorated with copper pipe, only problem is I spend more time buffing them than riding the bike.
Using the above method, I have never had a failure of a repaired thumb-shifter in two decades now.
Also, if the top cap is damaged, you can simply epoxy quarters onto the top, covering up the ugliness. Indian head coins look the coolest.
Lesser known thumb-shifter facts:
1...There's a hidden click at the end of the range. You can make 6 speed shifters work over 7 (six-speed-spaced) cogs, for example. Likewise a 7 speed thumbie will work over 8 cogs if they are spaced as a 7 speed. I often use the inner cog from a Ritchey 2x9 kit to give me a 33 tooth inner cog, with lower overall cassette width (less dish) than using a "standard" cog. Sometimes a small shim is needed for a clean shift.
2...You can adjust the firmness of the indexing: remove the shifter. From underneath unscrew the small #1 philips screw and pop off the top cap. The nut you see on top adjusts the tension(beware it's a left-hand thread: "unscrew" to increase tension). It indexes itself, so a couple of "clicks" is usually enough to change the setting.
3...You can disassemble and rebuild the thumb-shifters. Follow #2 as above, then back off that nut till the shifter internals come apart. Clean and re-lube, reassemble. I don't recommend this, all I have ever need to do in 20 years is flush with WD40, then dribble in some 30W oil, with no disassembly.
