Royal Purple in an 8.5 GN rear end with posi

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tobyp

Royal Smart Person
Jun 12, 2011
1,708
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Cincinnati, Ohio
Well after much conversation with the folks at Royal Purple about their 80/90 gear oil being ok in a posi unit I have tested researched and figured out that it is no good. not no good as a quality product, but no good for the clutches. RP states they have slip additive in the gear oil and that should suffice. After driving the car for a couple hundred miles and having the binding and chatter in corners on the gas I drained the RP and put Valvoline 80/90 with a slip additive and it could not feel better in turns. Just an FYI to everyone out there. I have been told that syn gear oil is no good on a posi, but RP begs to differ, I beg to differ back now.
 
synthetic oil doesn't break down as quickly, it is also a better lubricant, or "more slippery" to put it in lamen's terms. Also, synthetic oils have additional lubricating additives in them.

a posi additive functions opposite to what most people thing... it doesn't help the clutches grip better, in fact it actually helps them slip more. This gives a more comfortable ride around corners and is better for street use.

I made the mistake of using synthetic in mine, and I used additive ontop of that :blam: ... so now it's slipperier than ever.

best just to use non synthetic gear oil, with posi additive for road use. Could skip the additive for track use.
 
We use Valvoline synthetic and non-synthetic at my shop all the time. No problems ever - as long as you use the appropriate additive with it. I've never used RP so I have no personal experience there. I have heard many others say that RP is waaay over hyped as far as quality goes. Sure is pretty though :roll: .
 
I was thinking of doing the valvoline synthetic 75-90w and it says its recommended for limited slip on the bottle... i can also get a bottle of additive if needed. But wouldn't the oil have enough additive??
 
85GPLef41 said:
I was thinking of doing the valvoline synthetic 75-90w and it says its recommended for limited slip on the bottle... i can also get a bottle of additive if needed. But wouldn't the oil have enough additive??


I wouldnt waste the money and I have a 1200$ rear end. I have had plenty of people now say that unless you are drag racing it is not needed. So lesson learned on my side save the money and go conventional
 
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