Hey MarkRobert61.......Here is a pic of the gallon jug I used for the front diff and the rear pumpkin, and the smaller quart container of Mobil 1 Synthetic 75W90 I used in the Transfer Case.

https://cimg6.ibsrv.net/gimg/mitsubi...d928ed55c7.jpg

Up close.......this is API GL5, which is what is specified in the Shop Manual/Owners Manuals. Is there anything wrong with using this? Why should I use GL 4 when the manuals say GL 5? Help me here, as I wont be able to sleep until I know that Im not destroying the Transfer Case.

https://cimg3.ibsrv.net/gimg/mitsubi...d5f0b4f01e.jpg

https://cimg4.ibsrv.net/gimg/mitsubi...9bcc866563.jpg

Gl4
 

Ok, this gets a little technical: GL5 is a superior high pressure lube, but therein lies the problem. Under the pressure of the gear engagement a sacrificial layer is formed on the face of the gear teeth by the lube. As the teeth slide apart, this layer will shear off instead of the steel wearing. The problem is that Montys have synchromesh transfer cases. The synchronizer gears are made of brass, bronze maybe, and the sacrificial layer that forms has a stronger bond to the surface than the actual strength of the brass itself. Every time the shearing occurs, it takes a little brass with it. One of the guys on the 4x4 Wire had his synchros wear completely out in just a few months, the oil was iridescent gold when he drained it.

By the way, if you get a fluid spec printout from O'Reilly, it shows GL5 for the pumpkins and GL4 for the transfer case.

Gl4
 

By the way, the synthetics all say GL4/5 compatible, which is true for non synchro boxes, but only NON-synchro.

Markrobert61.......OK, I just checked the Owners Manual again.......and after reading that small fine print, you are right. It states that the Transfer Case takes GL4 75W90. I used GL5 75W90......dern it!

So, if I do not "shift on the fly" when engaging into 4x4, will this be a non-issue?

I usually buy from Advance Auto, and they do not have much to choose from. What brand do you use, and where do you buy it?

Gl4
 

Sta-Lube is the only one I have found. Napa usually has it on the shelf, it's only 2 quarts, so a gallon will do you for a long long time.

Gl4
 

Amazon looks like they carry it too.

Marks......Thanks.....I will check the price and will order some. But back to my other question......If I only shift into the 4x4 ranges when stopped, will this prevent that gear wear you were talking about (with the GL5 oil in the Transfer Case)?

Shifting GL4
 

I would think that only shifting while stopped would certainly minimize or eliminate synchro wear. There is a school of thought that says leave the rig in AWD all of the time... not that much fuel savings in 2WD...

Mark.......Good......I will not "shift on the fly" as long as I have that GL5 in the Transfer Case.

Leaving in 4x4 mode all the time......well, mabe if you out on the trails, but dont want to do that on the highway....just unnecessary wear/tear in my opinion, plus more "binding" on drive system.

AWD all of the time
 

Not an issue since we have a viscous center differential on these baby's, just one piece of the legendary and superlative Super Select drive system! I like the idea of keeping everything stirred up in the front axle and transfer case, lol!