Took my wife's kitchen aid gear head apart. The sacrificial worm gear fell
on its sword. Three teeth totally worn away. Easy fix as soon as new gear
arrives.

HOWEVER, while running the motor without the gearbox I noticed that it does
not run smoothly. Best I can describe is that it is 'hit and miss'
especially at the low speed. It kind of 'bucks' and 'jerks' while you
cradle it in your hands. The misses get fewer as I speed it up and are not
noticeable at the highest speed.

This is a brush (universal? ) type motor and the brushes are still approx.
one inch long. The mixer is labeled "solid state speed control" although
solid state components were not obvious to me. The speed lever is
mechanically connected to some sort of contact plate at the end of the
rotor. Moving the lever to higher speeds changes the angle of this plate
and for some reason the motor speeds up. There is a spring loaded contact
on this plate and if I push ever so gently on it the motor runs a lot
smoother and faster.

What is this mechanism (called a "control plate" in the parts diagram) and
could it be my problem?

All advice appreciated.

Ivan Vegvary