Lego Motor, repair
See also ...
Lego Technic Motor 43362 internals
Lego 9V Technic Motors compared characteristics
After one motor felt on the ground, it stocked and didn't rotate fluently anymore.
The cause was that one of the heavy iron plates had come loose.
So the first thing you could try is to give a shock (impuls) in the other direction, which may position the iron plate back in it's position.
Before cutting it open as I did, you can try to remove the 4 locks, of which 2 can easily be reached and the other 2 are difficult to reach. Because the locks are done by melting just a little bit of plastic, the can be scrapped away be a small, sharp srewdriver.
Removing the upper iron plate is quiet difficult, because of the huge magnetic force !
Putting the plate back is even more difficult, because it has a very narrow fit !!
Remove the commutators? can be done without soldering,
remove the outgoing shaft, bend the wires and pull off the commutators.
Be carefully, because they are very delicate.
in series PTC1056 (2.5 Ohm), parallel BZW04P15B (BiDirectional Transzorb 17..20V).