In Reply to: Re: Hydraulic Fluid Sources and Type posted by Larry Holbrook on March 12, 2019 at 05:57:41:
The originally-specified 80 or 90 weight gear oil is probably a better transmission and final-drive lubricant
Another popular oil myth. Perhaps true of the economy fluids like the Xtreme product but definitely not true of a premium heavy duty UTTO. Take a look at these data sheets from Castrol, Shell, Mobil, and Valvoline.
Mobil Fluid 424
Shell Spirax S4 TXM
Castrol AgriTrans Plus 80W
Valvoline Premium Universal Tractor Fluid
All of them claim Ford M2C-134D, John Deere J20C, and API GL-4 level gear oil performance. The Xtreme product does not. Also notice the difference in the physical properties of the premium oils vis-a-vis the Xtreme product. The Xtreme product is not a premium heavy duty UTTO and does not claim to be.
You can get the level of final drive gear oil performance you want/need using a UTTO - all you have to do is open your wallet a little wider. The name brands are all $20+ per gallon but you can do a lot better for a lot less money by stepping up a few dollars with an inexpensive heavy duty generic.