Before you go out and buy S.A.E. 90w oil, you must find out if you rear contains hypoid gears. I have a ‘52 3100 and I use 90 weight multi-purpose gear lubricant not the 90 weight mineral oil that I use in my tranny. There is a caution in my shop manual that states “CAUTION: Straight mineral oil must not be used in Hypoid rear axles or two speed axles.”
I would suspect your’s is the same, but we need on of our “experts” to chime in.
Last edited by Phak1; Thu Mar 18 2021 01:02 PM.