I see. Sorry for the misunderstanding. I was looking at the 47-52 service manual. If the earlier 4-speed has an additional plug in the tail portion, I would assume that there's no transfer between the main gearcase and the tail housing that has the u-joint. If that's correct, then there wouldn't be a problem with overfilling the rear axle UNLESS the seal in the torque tube is leaking. Again, I'm assuming that the earlier torque tube is similar to the ones in the AD 1/2 tons.
