While at the Ford dealer today, I picked up the differential oils for both axles as well as the friction modified for the Traction-Lok. (Sorry guys...just can't say "posi" for a Ford or Mopar.)

The rear calls for 75-140 synthetic gear oil, while the front (from what I read on-line) uses 75-90. The counterman tells me that Ford has discontinued the 75-90 for the front axle and now recommends the synthetic 75-140.

Does anyone have a thought on this? I bought enough to do both axles while I have the covers off. The 75-90 still shows up on line...but he's never been wrong about stuff like this before.

 

I can point you to the Dana website but it is likely to confuse you even more then the ford guy just saying use this stuff.

The Dana specs vary depending on if the gear oil also lube the wheel bearing, how the axle is used, oil type and ambient temp.

Bottom line a synthetic 75w140 will work just fine if your operating in ambient temps of 40*+

From the Dana website
http://www2.dana.com/pdf/WESM-0060.pdf

 

On that Dana chart are all of the degrees F missing a (-) before the number? Kind of seems that way.
40F = 4.44C but -40F = -40C, pretty sure that minus sign is missing from the F column.

 

I think so as well but couldn't find a second source to confirm it in my quick scan.

But considering -40c is also -40f I assume so.

 

Thanks for the help pirate!!!