The most common symptom is slow or no rotation of the armature when the brushes get too short to make good contact with the armature. Another common problem is the bushings getting worn enough that the armature drags the pole shoes under load. That's indicated by shiny spots on the armature and the pole shoes. Once repairs get beyond changing brushes, bushings, and the drive gear assembly, plus machining the commutator, the cost is usually more than a good reman unit will cost. I virtually never change an armature or field coils- - - -too much work and expense!
Jerry
