My Instruction Manual for F-20, published in 1939 says: Transmission, Rear Axle, Steering gear
Summer SAE 160 min. temp above 40 F
Winter SAE 90 min. temp below 40 FQuote from the book:
"The preferred lubricant should be made from mineral oil and should be free from solid materials, which are undesirable for ball and roller bearing lubrication." This used to be referred to as "gear oil." Don't know what it's called today. Also don't know if there are multi-viscosity oils that would take the place of the two viscosities. I grew up on 10-20s, F-12s, F-20s and "Regulars," and I'll have to say that I never heard of a farmer changing the tranny oil for the winter, at least where I lived (NJ, 0 Fahrenheit possible, but uncommon). I think that once the tractor was driven for a few minutes, there would be a bit of heat generated to thin out the oil enough to lubricate properly. Don't quote me--I'm an armchair engineer. The F-20 transmission has straight gears all the way to the differential (no bevels, like in a rear-drive car differential). Rear-drive cars since at least the early 40s have spiral-bevel gears, and require Extreme Pressure (EP) oil. Don't know if there is any reason not to use it in straight gears, but it is something you could inquire about. You might ask around at service departments of a few tractor dealers and see what they say about oil in these old birds. I don't have any references handy for the H and M series, but these transmissions and axles were similar in the basic straight design of their gears, and I would think the oils recommended for them would be OK for the older tractors. Case-IH dealers would probably have information about H-M and SH and SM. Asking about F-20 today might get a "Huh, what's that?" Contacting some of the big oil companies should be easy on the net, and might give you some options. It is obvious that the company recommendations were for tractors that were going to be worked hard. If the tractor is primarily for show, the lighter oil might be fine year round. If you're going to farm with it, or use it in pulls, I'd suggest making some inquiries--a couple of ideas below. The oils in my youth were all straight mineral oils--no additives. Maybe modern oils have different characteristics, and that would be something to ask around about. I hope this is helpful, or at least food for thought.
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