If so, your motor may just need a good cleaning/servicing.
To get started, you will need a pencil eraser, a razor blade, and fine grit sandpaper.
Take the brushes out of the motor (they are the metallic blocks held
in by a spring loaded wire on the plastic end of the motor), do not
lose which one goes on which side.
Cut the pencil eraser into a long block that fits
through the brush's old slot on the motor. (Sometimes it helps to stick
the modified pencil eraser on a paper clip wire or some thing) make
sure you can reach the armature through the slot. (This is the copper colored
shaft.) It's important not to push hard or the eraser will flake onto
your armature.
Rotate the motor with the eraser in place.
Pull out the eraser. You will see that the end is very dirty. Take the razor
blade and cut the dirty end off the eraser. Repeat steps 1-3 until the
eraser is no longer dirty.
Wrap a piece of sandpaper around a pencil
and sand on the brushes until the black is gone. Match the "roundness"
of the end of the brush where it meets the armature. That is the only
part you need to sand.
Reassemble the motor and put a few
drops of oil in the ball bearings of the motor. Your motor will work
like it is brand new! Best of all, you can do this yourself for free!
