I have a 2009 F 450 with the 6.4L. Currently have a Dana S110L limited slip diff. I want to put in a Eaton True trac rear diff, However Eaton is telling me they are not sure if it will work due to the oil differences. It will psychically fit, but possibly not work. I see my truck uses a synthetic from the factory, and Eaton tells me unless I put a regular oil in with there diff, then it will not lock up. So since I am swapping out the diff for the Eaton, can I use regular oil? Or will that destroy the bearings and other components on the rear end?

Summery-
Ford calls for synthetic oil if I put the Eaton rear diff in, can I put in regular oil like they call for.

 

im not sure but if their diffs work in 250 and 350 with synthetic oil why wont it for in the 450 and 550 axles?

 

I put an eaton true trac in my 04 f350 v10 before winter used syn. oil, works great!

 

If the lube matches specs, I would run it! Synthetics are made for less maintenance intervals. To me all that means is it protects longer, and may handle heat better, for longer. On that note, I ran Synthetic with my TruTrac on my 9.75" rearend on my F150! (I know it wasnt under the stress and weight of your 450). On another note, you could try it with synthetic and dino, and see what works better! I am betting that it will work fine with the synthetic!

 

It won't hurt bearings or gears to run regular gear oil