I am about to install my used Motive 4.10's in my 95z, and was reading the backposts and saw some disagreement between synthetic and non-synthetic. I am assumin I have the auburn posi, and was considering running two bottles of Mobile one synthetic 75-90, and one bottle of gm additive. Is one bottle enough to treat this, and is this what you would recommend?
Thanks
Brandon

 

I believe in the dino-juice and not the synthetic, but I realize I am a Neanderthal. It's cheaper (by far), it has worked for me for 40 years, and I have never had a rearend failure that was in any way lubrication related. IOW, I never wore one out, just broke them!

Don't forget the friction modifier additive (GM's works for me).

Rich Krause

 

And for the counter point.
What you describe is what is recommended by GM (right in the owners manual) for that same set up in my 98 SS.

 

I have been told by Eaton that you should not run synthetic when running a posi. The synthetic will glaze the cluthes in the posi and allow it to slip.

 

Yes, I too believe it's too slippery for a posi setup. Don't forget that the posi is friction device. The clutches in a posi are designed and setup to work with the dino stuff.

Rich Krause

 

Thx for the responses. How much additive is needed to treat the two bottles of oil, 1 or 2 bottles?

 

One bottle of the GM stuff works for me.

Rich Krause

 

If that's the case then why does GM recomend it in the owners manual of my 98 SS with an Auburn posi?

DTS told me that the reason for not using synth with an Eaton HD posi is that the synth reacts with the bonding for the Kevlar clutch facings and will let them come loose.
I use what the manufacturer recommends. Synth in the 98 with the Auburn and dino in the 2000 with the Eaton HD posi.

Now even after saying all of that dino fluid will never hurt any rear. posi, open, Torsen whatever. So if in doubt use dino.

 

Al: I think you hit the nail on the head. Some posi's, apparently Auburn among them, recommend synth. With others it's a bad idea. For me, if I had an Auburn, I'd decide based on how the unit operated. If it was chattery/grabby I'd try smoothing it out with the real slippery stuff. If it seemed "weak", not gabbing hard enough and not spinning both rear tires eaually when burning out, I definitely go dino. Think of it as rear end "tuning" of a sort.

Not a biggie either way though.

Rich Krause