I have a 1946 3600 ¾ ton truck that I am in the process of getting running. I am getting confused on the lubricant for the transmission and rear axle and having a hard time finding SAE 90 lubricant. I found an SAE 90W Mineral Gear oil API GL-1 at NAPA which seems to be okay for the transmission. The manual says not to use mineral oil lubricants in Hypoid rear axles. If I am reading the vehicle information kit correctly it looks like the 3600 has spiral hypoid final gears. So it sounds like I shouldn't use this in the rear axle?
