Originally Posted by
Jimbo1983
I've found when trying to unstick these things, in addition to a good lube/flush, it helps to have a shifter cable threaded into them also. This way you can pull on it while you operate the lever to simulate the forces they would normally be trying to work against. I don't know if this is just my experience or if it works for others too, but I have gotten several old, sticky Shimano shifters to work this way.
In many cases, you pretty much have to have the cable tension applied to get the spool itself moving, and it's a really good idea to be sure that the the spool isn't rotating against any gummy resistance that could become worse, especially it seems with the MTB shifters. The spool assembly is somewhat like a stack of plates, and there needs to be a good distribution of light lubrication to keep them turning freely.
The force applied to the pawls by the cable during shifting, against the force of cable tension, effects a good, final working-in of the oil applied previously, though a gummed pawl that has been oiled (but not fully freed up with hot oil soak and/or being pushed around with a screwdriver) often shows a return of sluggish movement when
colder weather returns.
One more thing that seems to more-fully displace gummy grease from the pawl pivots is to grip the pawl with needle-nose pliers and gently tilt it very slightly off-axis, back-and-forth as the oil creeps in at both ends. Once the oil gets through the full length of the pivot, you'll notice how snappy the pawl moves in response to it's meager spring force.
Note that the pawl spring, where it hooks around the pawl, is vulnerable to careless application of force with tools, so best to clear any grease off the obstructs your view of where the nearly-invisible spring is hooked. I had to repair the end of one of these springs once, and it wasn't easy.
The all-too-common blasting of the internals with solvent sprays like WD40 has a tendency to restore free motion quickly, but with pawl sticking returning when the solvent dries out and the grease re-thickens. A more repeated application of the spray with repetitive working of the levers can make for a longer-lasting service, but it takes a lot of effort to get the grease flushed out of the annular spaces along the pawl pivot bores.
But since spray-outs of the shifters done in-place are such common practice, I will advise that the bike should be pointing at least 30 degrees downhill when this is done, so that, with care, lubricant might be kept from creeping in under the rubber lever hoods, which is a bit of a disaster once you go to ride the bike.
Note also that spray-outs of the installed shifters usually floods the upper cable housings with contaminated lubricant, which may affect one's cable servicing requirements and/or cloud the viewing window of optical shift-position indicators.