Ray Field wrote:
This is more electrical than machine shop but somewhere in the collected
wisdom of the group will be an answer.
Normally an electric brush type motor will have "no"sparking at the
armature, what does sparking indicate and what is the cure.
This occurred on a built-in vacuum cleaner motor. Relay/switch module
failed, bypassing the module allowed the motor to run normally. Pulled the
brushes, lots of brush left and free movement - reinstalled brushes in same
position lots of sparks.
All advice appreciated.

I've done a fair amount of commutator turning and small motor repair.
If the motor has had a lot of use, the commutator can be grooved and
pitted or adjacent bars can even be shorted by accumulated brush dust
and gunk. If you didn't get the brushes back into the same holes they
came out of, you'll get a lot of sparking until they wear in again. I
had one commutator that was like .030" eccentric, that one chewed up
brushes like crazy until I turned it. On some DC/universal motors, you
can move the brush holders until they're in the best position where
sparking is least, not many small motors have that feature but it's
handy. You'll always get a small amount of sparking, but it's not like
the ring of sparks you'll get from bad brush position, poor brush fit
or a shorted commutator bar. With the proper tooling, it only takes
like 10 minutes to turn a small motor commutator and maybe that much
again to undercut the commutator grooves with a hand tool. I usually
use a ground-down hacksaw blade for that. On some vacuum cleaners,
getting the armature out is the toughest part of the job, they really
want you to toss the whole works and buy a new one.

Stan