Hi guys. I have fitted a brand new truetrac centre with 3.73 diff gears not long ago. Just like to know what grade of oil should i use ?
I am currently running Penrite pro gear GL-5 75w85 syn.
I have searched and googled and found you should use a GL-5 lubricant 75/80w-90. That's in USA by summite and other diff blokes up there. But here in Aus all the diff blokes are recommending 80w-140 which i feel is too thick because i have tried it. The reason why i'm saying that is that my truetrac didn't work well. I even rang Penrite and they couldn't tell me exactly what grade to use. Just like to know what you guys use, recommend or know.
I would like to stick with Penrite lub but will consider.

Eaton recommend using a mineral oil with no friction modifiers fro Trutracs. Unfortunately, the majority of diff oils are synthetic. Nulon Premium Mineral 80W-90 Gearbox & Differential Oil might be what you're after.

Thank you very much Shortshift. I have decided to use the Penrite Pro Gear 75W-90 Syn.
I have spoken to Penrite tech and even he doesn't know the correct answer but did tell me that the Pro Gear 75w-90 is the best oil in that grade and will do the job.