Originally Posted by
Road Fan
Both left and right have gone sticky. I'm not sure yet if it/s just cable/housing, or in the units.
The left one does not click into the big chainring position, and the thumbkey on the right does not slip back when you depress it. If I pull it back and forth, it will dump the chain from the big chainwheel to the smallest one.
First step is to remove cables and check for excessive friction. You may need new outers.
Second stage is to fire some GT85 or similar into the shifter. Usually does the trick. As has been said above, they are generally very reliable units so I wouldn't imagine anything has gone too far awry.