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.