tomss99

i heard that your not suppose to use synthetic gear oil for eaton posi's....is this true?? and that instead of the normal 75w90 your suppose to use something different.... i already bought my royal purple 75w90 this sucks.....what am i suppose to use than?

Blacker

iTrader: (3)

No synthetic with the Eaton Differential. They recommend 80W-90 Mineral Based Gear Oil with 4 oz of GM Additive since it uses clutches. The synthetic can caise more slippage.

electricz28

Where did ya'll hear that line of bull.......

Inspector12

iTrader: (29)

I was told that it was to due with the material the clutches were made out of not more slippage etc... Good luck!

JEB99TA

iTrader: (32)

That's the first thing I read in the instructions that came with my Eaton unit. It explicitly says NOT to use synthetic.


Here's verbatim what the Eaton Instruction card says, which comes with the Posi:
If you want a picture of this, just send me your e-address and I'll send you a picture of the instructions.

Blacker

iTrader: (3)

I would take the manufacturer's advice over what the "internet" says

ETS

Synthetic lube doesn't affect performance but it causes chatter during normal use. It's lighter body doesn't seem to cushion the clutch disks as well as mineral oil with additive. I'm a tech at Eaton and about 4years ago when aftermarket program started up we used synthetic for all out testing but after a few months the differentials really chattered and mineral oil was the cure to keep the carbon disks quite.

JEB99TA

iTrader: (32)

So, what's best for the life and health of the posi unit? ... synthetic or non-synthetic? The instructions clearly warn you not to use synthetic, but, you're saying you're a tech at Eaton and synthetic is fine except for the chatter and noise? Sumpthin' ain't smellin' right here.

ETS

Well synthetic and mineral oils both pass the durability testing that we need to run to validate the disk life. The synthetic oil will develop chatter sometime during it's life span. Thats not a guarantee but theres a pretty good chance it will. Synthetic with the recommended friction modifier will prolong the onset of chatter or sometimes quite a noisy unit but mineral oil is the recommended and the best oil for the job. I was just mentioning that either oil will do the same job but the synthetic has an unwanted side affect and mineral oil doesn't.

electricz28

This isn't an FDA product-whats up with possible side affects. The rear end is probably one of most neglected parts on cars. I mean if the rear end is doing its job how often do most folks check it. Like when they do simple oil changes. I don't know about anyone else but i just dropped a chunk of cash to put this Eaton in and would like to keep it for awhile.

ETS

The only side affect is chatter with the synthetic lube. Doesn't hurt the life of the unit. With syn it might make a chatter noise when your doing tight parking lot turns. It won't wear anymore or cause reliability problems, it's just an annoying sound. This isn't even a side effect if the instructions are followed because they recommend the proper lube in the first place. I'm just stating that syn. can be used but chatter is the only side affect. It's not gonna wear anything out any faster. All of the siverado/GMC trucks with the G80 locking diff use the synthethic lube from the factory with similar clutch paks so you should know that wear isn't an issue. The preload plates of the limited slip cause this chatter and the mineral oil insures that the noise is kept to a minimal.

electricz28

The mineral oil will probably need to be changed every 7,500 miles and will definately break down the faster than synthetic. I know it can't take the heat and probably doesn't have the aint-foaming additives the synthetic has. This is all just personal preference anyways. Good luck

JEB99TA

iTrader: (32)

If noise is REALLY the ONLY side effect of using Synthetic, then, I'm using synthetic. My exhaust will drown out the noise ... LOL!

electricz28

with the c/o open you shouldn't be able to hear the radio :