About two years ago I tried to rebuild the original wiper motor with mixed results. In the end I just bought a new motor and that worked fine. For a couple of years. Then one morning I tried out the wipers and nothing happened. I took the motor off and brought it to the work bench for disassembly. Once the stator housing was off and the plastic wiring harness with the brush wires and EM suppression capacitors out of the way it became clear what had happened.
At the base of the motor where the worm gear on the rotor enters the housing of the spur gear that it drives, there is a sort of primitive thrust bearing that keeps the rotor in place. This bearing assembly is actually three parts. The main part is a brass sleeve bearing through which the rotor is inserted. The “top” end of this sleeve is somewhat tapered so that the second part, a short spring, can sit over it. The third part is a washer against which the spring pushes. The washer is meant to be held in place on the motor’s housing so that the spring has a solid place to push against thus putting tension on the bearing sleeve to hold it in place. The washer is normally held in place by means of small stakes in the lip of the space where the whole thing lives. Here is how it’s supposed to look on the original motor
Notice the six indented sections of the lip that act as a sort of claw to keep the washer in place. The new motor didn’t have anything nearly like that. So with a flat bladed screw driver and a hammer I made a few of my own.
Everything got some new grease before reassembly and went back on without issue. The only change was that instead of the crappy plumber’s putty that I had previously used as weather sealing I used 3M caulk strips. These will definitely hold up better in the long run.
Next up: a new bit to swap out!