Is this the vintage with the selector clutches, chains, etc? What a monstrosity.
I'd compare the generator field voltage, loop volts, and motor field voltage with a good running car. Maybe you will see the gen field drop much lower than the other car when it's in leveling. Then watch the other car come into floor level, and note what relays change states, that put the unit into the proper leveling speed. Maybe you have a bad contact, or a resistor problem, open coil somewhere.
Sorry I don't have anything more tangible to say. I've never worked on that stuff.
