You are taxing my memory, but we used to reverse those bull pinions and so they have the same thread. If you have a hydraulic unit, drain the oil from the rear end first. If you get more than 5 gallon total out of transmission and final drives you need to replace the seals in your hydraulic pump. I think I have a cross over sheet for the bull pinion seal. There is also an O-ring inside the bull pinion.