My wiper motor in my '66 has been acting funny for a while (kind of jerky) so I took it apart to see what was wrong. I found a cracked brush and I replaced them but since I've reassembled it I can't get it to work on low while doing the bench test. It will work on high speed but if you jumper to low it will run for about a second and then stall. Also I assume that it's normal for it to 'surge' while running because of the park switch? I did all the normal VOM check to the armature along with taking a pick and scraping out the gaps on the commutator hoping that maybe that was part of my problem. My commutator looks like it's got a lot of wear on it and the old brushes were half the size of the new ones. Any thoughts or should I just quit fooling with it and get a rebuilt one?