Going Synthetic, what brand is best?
 

That's right, I took the plunge and switched over to Mobil 1 Synthetic today. That's 6.6 fewer quarts of petrolium product every 3 months. Now I need to get the transmission and diff fluid changed over. I hear going all synth is worth another 5-10 whp. Every pony counts! :)

Does anyone know a reason to choose a particular brand of tranny or diff oil? I've heard good things about Amsoil, Royal Purple and Redline. Is there really any difference between them?

going synthetic on tranny? I might be wrong but I remember my T-56 requires non-synthetic... But you might have a different transmission or i might be remembering it wrong. Hell I don't know crap why would I reply :)

As long as you put in the posi additive in the dif you will be fine going with synth. As for which brand is best, according to the research I did a year ago, Redline rated the best (by about half a pubic hair). Royal Purple was 2nd. And in 3rd (maybe an entire pube back) was Amsoil. I was running RP throughout & loved it (because it's cheaper than Redline). I now use Amsoil (because Tranzor is a distributor). And I have heard issues with the lightweight Redline in the dif.....

I know the eaton posi in my pickup specifically says not to use synthetic in it. I assume you have the stock rearend, so I don't think there's a problem with it in there. Just something to think about that all diffs don't like synthetic.

My diff addendum (Auburn for SLP) says no synthetic as well... I think the main reason is it gradually eats through the liquid gasket.

I know there are guys here on Tech and and over on the "Duece" who actually send samples of their car's used oil/products out to labs to be tested and what not. The general feeling seems to be the German Castrol Syntec is best for the motors....although I don't know by how much but I don't think you will go wrong with proper care, maintenance, etc with any of the top graded synthetics. I know I am not the know-all guy for this stuff, but that is my $.02

This is really interesting cause my Auburn Posi from SLP came with Synthetic fluid??? Just had NW Dif service my Diff. Had him do Redline With the highest Viscosity.

I'll dig out the paperwork this evening and post it up... :judge:

I read this as well. There is conflicting info in the paper work from the factory about the rear-end fluid when you buy the car. On a seperate peice of paper stuck in the manual there was info on the SLP stuff. Anyway one thing said use synthetic and the other said not to w/auburn diff. But you need to use the additive with the auburn. I forget whats in there now, but its petroleum. My diff works fine. Leaves two even strips when ever I check :jest:

I'm sure the GTO is safe with synthetic diff oil. It comes with it from the factory. The 2006 GTOs are even coming from the factory with synthetic motor oil.

From the owner's manual:

"Rear Axle - SAE 75W-140 Synthetic Gear Oil (GM Part No. 89021809). With a complete drain and refill add 1 oz. (25ml) of Sturaco 7098 Friction Modifier (GM Part No. 89021958)."

There are lots of local stores near my place with Royal Purple, so with little or no difference between products, and with RP saying the friction modifier is already in the product, it makes them an easy choice. 5 qt Synchromax and 2 qt 75W-140 here I come.

*Edit*

Well, the deed is done. Took her for a test drive and shifting is a little smoother, but not too big of a difference. Launching, however, is noticeably smoother. The rear doesn't complain at all now. While I was at it I gave my line lock a thorough testing. A big cloud of smoke is now an easy thing.

Remind me next time I change these fluids on a car...find a friend with a lift. Trying to work the bottles and squeeze that stuff out against gravity while lying on your back is a PITA.

Now I'm ready for racing, and hoping for Friday off so I can get out to Bremerton. :drive: