Suntour Mighty thumbies - slipping ... toast?
 

I have a very used set of Suntour thumb shifters like this (below) on my mountain bike (converted to dutch-influenced frankencommuter). Only if I torque the bejoozes out of the screw on the top will they even think about staying in gear.

One of them makes no ratcheting sound at all, and the other only sometimes.

Does this mean that the ratcheting mech is worn out and that's just it? Retrofits? Some way to add a washer inside and make them pure friction shifters?

Thanks.

http://www.oldbicyclejunk.com/zencar...ge.275x206.jpg

I've got a set like them that are friction/index for the rear and friction for the front. The index can only be used with the a3000 derailleur and is very finicky. The friction mode works fine. The left shifter, however, for the chainrings is a pain - it's got incredible resistance regardless of cable tension or how tight or loose the screw on top is. I've pretty much given up on them.

thumbies ,see that little screw,disconnect cable,remove thumbie, undo screw,underneath there is a ratchet wheel and spring ,these sometimes fail or are dirty.the springs are the same as the old suntour bar-end shifters[as possible spares] good hunting

I'm about to install a pair of these on my bike. I hope it goes well.

I have those on my Utility bike, and they are probably the best shifters thumb shifters I have, really like them a lot. mine have no index option, just friction. I'd say a carefull disassembly and cleaning might show whats wrong.

I have a set of suntour power stem shifters that I took apart for the same reason, one side was not ratcheting. the whole ratchet mechanism was missing. The guy had been shifting with them for years just on the tension of the screw.

If the internal mechanism is complete there's a tiny ball bearing that is spring loaded against "serrated" edged rotator/wheel. This what enables the ratcheting/locking action in friction mode. The works may be gummed up or there may something amiss with the bearing interface. Maybe the ball is missing, altogether. In any case, be careful on disassembly or you'll lose the ball or spring.

This is a friction shifter that benefits from a tiny bit of grease on reassembly.

BTW, there is no indexing capability with the shifter shown. Its a variation on the more common barcon.

J

I love these shifters... but I'm a Suntour hoar (got around the censoring software... neener-neener). I have three sets of the barcons and one set of the thumb shifters like yours.

The mechanism that these shifters use is very simple and extremely durable. The only way that I can see to break them would be to completely wear out the pawls on the little toothed wheel inside... but there is little or no pressure on the catch plate that rubs on the teeth. Looks like it would take about a hundred years of regular use to wear the teeth off of there.

Take it apart and clean it up. Reassemble the thing with just a smidgeon of grease on the pivot points for the gear wheel and spring plate. I'd wager that it'll be as good as new.

If not... send them to me! :D