I know for sure that the G80 calls for 75w-90 synthetic, not sure on the open diffs though.

Those of you running Detroit TruTracs, be sure to use conventional gear oil or the TruTrac may not operate properly. This is as per Eaton, and has been proven here more than once as observed by folks running syn in their TT's, and the diff not locking as it should

 

The Eaton Truetrac notes to use whatever lube the OEM uses.

I thought the issue with the Truetrac occurs when people add friction modifier to the mix, not from conventional to synthetic.

I remember someone here added friction modifier to their Truetrac and it wasnt performing correctly, then they changed the fluid and didnt use friction modifier it was fine.

Eaton Corporation - Industrial Products, Services and Solutions

I dunno.

peace
Hog

 

Regular clutch type eaton uses reg oil correct?

 

There was some debate about this here a while back, and one of our members called Eaton, and they were told to only use conventional gear oil with the trutrac. A few guys were running syn and their TT's wouldn't lock, but once they switched to dino gear oil, it functioned as it should.

Not sure if it makes a difference for that one, although clutch style LSD's will use a friction modifier (aka whale sperm)

 

Correct. Eaton's paperwork specifically states to use a non synthetic 80W90 with the clutch pack LSD's. Of course stating you need a friction modifier with it as well. I just installed one in my beater Caprice in November that I sold recently ( should have kept the LSD). Why synthetic won't work I don't know but that is just Eaton's recommendation.

 

The correct amount, according to the owner's manual, is 5/8"-1 5/8" below the fill hole on the side of the housing. That's gonna be right around 2 qts.

Don't make the mistake I did of filling until it was almost pouring out of the hole on my TA cover. That was around 4qts & those extra 2 qts came out on a long trip, covered everything under my truck from the back of the cab back.

 

you just rustproofed it

 

Synthetic in a clutch type posi (like an eaton) will make the clutches fail prematurely, it's just to slippery.

Also it's a good idea to try to run it without a friction modifier. If it chatters real bad when you turn put the friction modifier in. All the friction modifier does it let it slip easier making turns and such more comfortable, the clutches will live/grab better without it.

 

FAQ for Differentials

I can sorta buy the clutch pack arguement with regards to oil, and actually have experience with the oil selection issues. I have yet to see one new not chatter without friction modifier in the fluid. If the plates are partially worn out or glazed then not running the friction modifier is a cheap way to limp it along for a little while longer.

That said I don't understand the oil arguement with something like the locker. It's a mechanical locking diff, not reliant on clutches so really the oil choice should have zero affect on it's performance especially just going from conventional to synthetic. It's funny how they are reliant on an inferior refined lubricant to make their stuff operate as it's supposed to. Not to mention they build the garbage Gov Lock and it being a mostly mechanical operating nightmare, it can live on just fine with synthetic lube and has since around 1998.