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What's the written specs when it comes to gear oil??
Trans, transfer, differentials

I 'heard' GL-4 but can only find GL-5

Help
(In Huntersville)

If it contains yellow metal do not use GL5. Or any extreme pressure lubricant. They contain additives that destroy the yellow metal.
I have no trouble buying GL0. And GL4 isn't hard but you will have to order it.

just me wrote: ↑Tue May 23, 2023 1:59 pm If it contains yellow metal do not use GL5.
...
I have no trouble buying GL0.

Thanks. From my reading GL5 is not good.

What about GL1?? NAPA stocks it and it's relatively affordable.

If you're looking for transmission and transfer case oil, NAPA has a GL4 dinosaur oil made by Sta-Lube that is reasonably priced.
https://www.crcindustries.com/products/ ... 1-gal.html

Others on this board have recommended Red Line's MT-90 synthetic oil. I used it for awhile, but have switched to Sta-lube for the time being. MT-90 is expensive but you shouldn't be changing your transmission oil all that frequently.

There is also talk of Amsoil's transmission fluid being quite good, but I can't speak to that. Amsoil dealers often give veteran discounts if you're cut of that cloth. If you have an Amsoil rep in your family (they operate on the Mary Kay business model) you might be able to get a deeper discount.

not long ago, spoke with Charles T. up a his shop, and he suggested that while he has used other trans lubricants, he believes this one is really a good choice. It is what I recently filled my transmission with. Got it via I think Amazon or Target as I recall. My transmission has always shifted with ease, with perfect synchro function. Maybe just lucky. Hal

Tractor Supply has a product made by Travelers the is GL 1 manual transmission fluid for Ford Tractors.
Has anyone used this product?

I also use the Amsoil SAE 50 Long-Life Synthetic Transmission Oil that Hal mentioned. I've been very satisfied with it. It's safe for yellow metals, smooth shifting (even in cold weather), synchronizers are working well. I've put about 7000 miles on the truck. The first 750 or so were with the 90 wt gear oil the previous owner had in there. I could definitely notice a difference when I switched to the Amsoil.

This stuff is expensive, but you can get a significant discount if yu signup for their preferred customer program.

A note on viscosity: Don't be fooled by the numbers. SAE 50 oil is the same viscosity as 90 Wt gear oil. They are two different scales. (ISO VG 220 is also the same viscosity). I searched this info out when I first heard Charles' recommendation for the Amsoil SAE 50 oil (worried that it would be "too thin" for the transmission). I also spoke with a technician at Amsoil who confirmed that if it were rated on the gear oil scale, it would be a 90 wt, which is exactly what the Technical Manual / Lube order for these trucks recommends.