UPDATE: OK got the Differential Fluid changed. There are two tags bolted on the Differential. One has identification numbers and the other has the oil viscosity indicated. Mine says 75-140. The Owners' manual does not say anything about rear diff oil viscosity. The owner's manual tells about the front transfer case but nothing about the rear (strange, I wish they write in there to check the tag).

So you have to look on the differential tag itself. I had 75-90W so I had to return it to get 75-140W. The other issue I found that all 75-140 are designed for Limited Slip differential but can be used with GL-5 or GL-4 type oils (at least that is what the Shop said, we will see).

I used Black RTV silicon along with the gasket. I will wait overnight before I drive the truck, just so the silicon cures overnight.

I removed the spare tire so I have more space to sit underneath the truck. Jacked it up on jack stands just two inches. The 3/8 nut came out relatively easy.

 

ok sounds good. what was your method with the RTV? havent changed mine yet. how many quarts of 75-140 did you use?

 

Yea, that's been re-spec'ed by Ford to 75 140 , Per OASIS TSB. For OP,TL and LS 8" rear gear fluid.

Previous spec was 75 90.

 

I used a thin bead on both surfaces, attached the gasket to the diff cover, make sure you match all the holes properly. Follow the instructions on your RTV and place the cover and tighten the bolts.

I used 3 quarts

 

now i know lol !!!!!!!!!

 

Very good. Thank you for the tip.

 

That's alright, - just change it out sooner. 40 or 50 thousand miles.