Transmission oil for M37

[slk]

Hey guys what kind of oil goes in the transmission & how much. ? Also where is the fill plug and where is the check level plug? Can you mix oils?

Steve

[John Mc]

I used Amsoil SAE 50 Long Life Synthetic Transmission Oil In my freshly rebuilt transmission and transfer case.

I believe the lube order calls for 90 weight gear oil above 32˚F and 75 weight for temps from -10˚ to 40˚F. Lubes have come a long way since then. A lot of folks are using 75W-90 gear oil to cover a wider range of temperatures. I went with the SAE 50 Amsoil synthetic oil because it works better when cold (no stiff transmission until it warms up as with the higher viscosity oil, so things are getting lubed right from startup) and resists heat better than the old single-viscosity gear oil which was the best thing available back when these trucks were in production.

[NAM VET]

Concur, Charles Talbert uses the above synthetic 50 wt transmission oil in his truck's transfer cases and transmissions. You have to be sure to use a transmission oil compatible with brass in the transmission. The transfer case takes nearly four quarts, with the fill plug on the driver's side of the case, the drain plug also a big NPT on the bottom. Same for the transmission and fill. I got my two gallons of the Amsoil products directly from Amsoil. I use an autoparts store suction piston device with a plastic tube to fill them, and have also one with a metal fill tube. It is a messy thing to do. NV

[John Mc]

Yes, Charles at M-Series Rebuild is where I first heard of the Amsoil transmission oil.

I'm also using the Amsoil Z-ROD 10W-30 Synthetic in my engine. Oils with added zinc are not as common as they one were. This stuff has it, and is a top notch oil.

Both are a bit more expensive, but if you join their preferred customer program, you get a discount (about 25% on the transmission and engine oil), and if you buy $100 or more at a time, shipping is free. I just buy my oil a case at a time to get the free shipping. Even with the discounts, it's more expensive than a lot of the off-the shelf oils in the auto parts store. I figure with a freshly rebuilt engine, transmission, and transfer case, I'd like to take care of them well from the start.

[sturmtyger380]

As another option I started using this years ago and am pleased with it - Lucas Oil - Synthetic 50 WT Transmission Oil:

https://lucasoil.com/products/heavy-dut ... -trans-oil

[John Mc]

Lucas Oil does make some good products. That transmission oil is a bit less expensive than the retail price for the Amsoil product (however, the Amsoil stuff drops to slightly less expensive if you sign up for their preferred customer program)