In Reply to: 640 posted by Leroy on March 04, 2018 at 19:25:18:
M4864A was a mild EP SAE 80 gear oil which Ford recommended for year round use in all three sumps of the Hundred series tractors. Because that oil was overly thick in cold weather the Ford Owner's Manuals all recommended adding a couple quarts of lower viscosity hydraulic oil (M4864D) to the contents of the hydraulic sump. As oil technology advanced Ford changed that recommendation to their newer M2C-134 oil which had a higher viscosity index and was better suited for year round use in all three sumps - no thinning needed in cold weather. The ubiquitous and inexpensive Universal Tractor Transmission Fluids (UTTF) sold today are generic equivalents for M2C-134 and the picture below is one of many brands available today. UTTF type oil has been widely and successfully used in millions of Ford Hundred series tractors for over a half century.