Does anyone have N-Scale Magazine CD Vol. one. I have a Kato EMD GP50 that I need to disassemble and there is an article on this model. It is Ron Bearden's article in N-Scale Magazine (July/August 1990, Vol 2, Issue 4, p. 35-37).
You also need to know a couple of other things. 1. The u-joint slips with age. Look for cracks and looseness. 2. The GP50 design is poor. The bearings rattle around too much. After you have insured the u-joints are OK, you can take a pair of pliers.... with the motor and worms installed in the weight, holing upside down, and gently pinch the lead weight where the bearings are held. This will make holding them tighter and the loco should quiet down.