I searched and found a thread, but it was from 2013, so things may have changed.
I am going to try to drain my diffs and transfer case this weekend. Just wanting to know what everyone thinks is the best oil and weight to run in them. If I am going to change them, I want to change them right.
Thanks guys.

 

Transfer case: Dex/Merc automatic transmission fluid

Diff rear: 75w-90 gear oil standard, 75w-140 for towing/offroad

Diff front: 75w-90, but you can use 75w-140 here as well if you want to

I tow and occasionally offroad, and I run 75w-140 rear, 75w-90 front.

 

If the diff is LSD, like Dana 35, I believe there's an additive you need to add to the oil.

 

^ Oh yeah. That too.

 

I just replaced my rear diff fluid in my 99 xj with a chry 8.25 rear. I used a felpro gasket with a light schmeer of ultra black rtv on each side, let it cure for about 2 hours and filled with amsoil severe gear 75w140. I'm rarely offroad but occasionally tow a boat.

 

I know the viscosity test i posted is for 75w90 but...gives a pretty good look at what gear lubes are decent, and what to stay away from.

 

I use the Wal-Mart brand gear oil and I have 85w140 in both diffs. Transfer case takes regular mercon atf. Also get lube locker gaskets for the diffs they are reusable and you don't have the mess and dry time with rtv.

 

^^^ what he said. LubeLockers are great, just not available locally for me and $30 online, a little outside my budget. I opted for cheaper gasket and better fluid.

 

two days ago i changed to 85w140 and transfer case is dex iii and rtv red

marc