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Hi guys I have a question. When servicing the transmission on my 1948 Super Eight what fluid should I use? Some places it says SAE 90 mineral gear oil and other manuals say SAE 140 mineral gear oil

Moodydavid16, Assuming we’re talking about a standard transmission I believe in the maze of service information available there is an observation that 90W should be used in the winter, especially if 140W produces difficulty in shifting. That same information establishes a one year service interval for that lubricant . . . except for those folks that live in cold climates, then it would be twice a year trying to keep-up with the viscosity requirement. If you don’t intend on using your car below freezing then 140W GL-1 should work OK . . . having said that I use 85W140 GL-1 year round in Phoenix AZ, but have been known to use straight 90W GL-1 from NAPA, again year round. To borrow a cliché from helicopter pilots, I drive those cars with soft feet, so 50 counts in viscosity doesn’t matter all that much. I remember after the first oil embargo some manufactures were servicing standard transmissions with ATF, presumably to get better gas mileage . . . they did make a lot of noise in low gear, but otherwise that ‘thin as water’ lubricant worked OK. If you decide to use straight 140W then a few extra minutes warming the transmission oil in the very cold weather won’t hurt. Even with the transmission in neutral as long as the clutch is engaged the cluster gear is spinning, and that alone will heat the oil.
dp

I believe most have settled on regular GL-1 90 wt gear oil for general use in the trans. In extremely hot climates some have gone to the GL-1 140wt or even the multi viscosity offering. If you have an overdrive the lubricant is shared between the units and in that situation it would probably be best to stick with 90 wt. The OD manual makes no mention of anything over 90 and actually suggests even thinner oil but allows the 90.

GL-5 85-140 which is an extended pressure oil is good for the rear axle but is not recommended in the transmission particularly if there is an overdrive involved. Borg Warner expressly states not to use any EP lubes in the overdrive.