Bicycle Mechanics - Sticky Thumbshifter. How to Fix?

The thumbshifter that controls my rear derailler is starting to stick. It is the thumbshift, which is the one that moves the chain to a larger, more innermost rear sprocket. When I depress the thumbshifter, it goes ahead and shifts ok, but often it does not return to it's "home" position. I have to use my index finger to push it back to it's normal resting position.

Anyone know a simple fix for this?

I'm having the same problem with my Alivio shifters, only with the front derailleur. I'm guessing something's wrong with the return spring (I still haven't gotten mine working). It has been suggested that shooting some tri-flow into the shifter might help, but it didn't help mine. I suppose it could be adjustment of the derailleur, but the shifting works flawlessly - I just have to push the shifter back to its starting position manually.

Hopefully somebody has some idea how to fix it. The shifter still seems to work fine...but it still bothers me! Haha

If the lever does not try to return at all, the spring is broken(new shifter time), otherwise some powerfull degreaser like Clean streak and some lube will free it up.
On some shifters, where both levers are below the bar, they can get bent into one another during a crash. Shift them back and forth while looking between them to see if they touch if so they can be tweaked apart with a flat blade screwdriver.

The alivio shifters tend to do that when the weather turns cold, it is usually the front shifter that sticks. I have tried many different thing to correct this but it always seems to go back to it's sticky ways when winter comes along. I generally replace them with the LX shifter and the problem goes away.

I have the EF29 Shifters (http://www.trekbikes.com/bikes/2004/mountain/4300.jsp).

Sometimes the shifter returns fine. Sometimes it has to me manually put back into place. The cold does seem to be a factor as I have noticed it more and more as the weather gets colder. My bike is only 2 months old so I may return it to LBS to see what they will do.

How do you lube this thing? It looks like you would have to break it open to do that?

Ranger, I've tried different lubes and have disassembled them and cleaned and lubed them, it never helped and sometimes made it worst.

I put a trashcan under it and then jet cleaner thru any available hole until it runs out clean. Sometimes I will take them off the handle bar and tank them but it is hard on the plastic parts. Taking them apart usually does not do any good, they are not meant to be worked on, no parts available, and can be frustrating to reassemble