If you do some searching, you’ll find just about as many discussions/arguments on the subject as you do with the ZDDP topic.
I worked in the commercial trucking industry for a numbe of years. Somewhere around 99/2000, manufacturers started recommending their own proprietary fluids in transmissions.
In the automotive world, companies like Tremec started recommending Synchromesh and Synchromax fluids in their transmissions. When GM started using Aisin Transmissions in Colorado’s they did the same thing. You’ll find the same trend elsewhere. If you look on the Valvoline spec sheet, they recommend Synchromesh for just about everything.
Here’s my guess. The GL4 and GL5 fluids have additives for hypoid and spiral cut gears that manual transmissions don’t need.
The Ford oil should be fine. The older tractors used straight cut gears, plus they used the trans/ rearend as a holding tank for hydraulics. They don’t need the additives either.
Last edited by Whitedog; 10/06/2018 2:12 PM.
