The lever body of Shimano's STI lever, excluding the bracket section, is
commonly called the "shifter head unit" (アタマグミ).
Shimano's approach to poor lever operation is to replace the shifter head unit itself.
↑This is the shifter head unit from an ST-7700 (early version), and
after downshifting, the large lever return was sluggish,
and during upshift, the large lever followed slightly behind the small lever's movement—
typical symptoms of a well-used STI lever.
The shifter head unit itself is like a black box;
complete disassembly and reassembly is basically impossible.
The sluggish shifter response is because dust has gotten into the grease on the internal gears,
but if you try to clean it out,
you end up with a dry, chattery feel instead.
The ST-7700 doesn't expose its internal gears, so
applying the right viscosity grease to just the right spots
is extremely difficult.
Well, I tried anyway.
↑With the later ST-7700B or C versions,
you can actually access it from the outside to apply grease.
This one's something different. Today just happens to be a day I'm working on 7700 levers a lot.
commonly called the "shifter head unit" (アタマグミ).
Shimano's approach to poor lever operation is to replace the shifter head unit itself.
↑This is the shifter head unit from an ST-7700 (early version), and
after downshifting, the large lever return was sluggish,
and during upshift, the large lever followed slightly behind the small lever's movement—
typical symptoms of a well-used STI lever.
The shifter head unit itself is like a black box;
complete disassembly and reassembly is basically impossible.
The sluggish shifter response is because dust has gotten into the grease on the internal gears,
but if you try to clean it out,
you end up with a dry, chattery feel instead.
The ST-7700 doesn't expose its internal gears, so
applying the right viscosity grease to just the right spots
is extremely difficult.
Well, I tried anyway.
↑With the later ST-7700B or C versions,
you can actually access it from the outside to apply grease.
This one's something different. Today just happens to be a day I'm working on 7700 levers a lot.