"Dark ages nonsense?" You have a small opinion of R&D and engineers who go out of their way to tell us to not use synthetics. If you purchased a brand new limited-slip carrier from Eaton, it would have a green tag attached that warns you, in big letters, to use mineral lube with the GM additive.

For limited-slip carriers, there's a "zone" between limited slip effectiveness and driveability. Through R&D, the engineers know how to achieve this "zone". In other words, with the incorrect lube, your carrier could lose it's positration effectiveness, or you could encounter chatter and bumping.

If you use a non-recommended recipe you need to test, with a torque wrench, on the end of a wheel, for the correct "slippage". I don't recall what the specs are; perhaps someone can provide it. Even if you're within tolerance, you still risk chatter from incompatibilty with the clutches.

Some newer cars recommend synthetics for their carriers; newer Vipors for instance. But you can rest assured, the engineers, through R&D, designed the clutches for use with synthetics.

I'm sure the shareholders of Amsoil, Red Line, Royal Purple, etc, would like me to purchase as much product as possible, but I'll take the advice of the engineers who design the carriers, R&D them, and study their failures (warranty claims).

Anybody want to guess how many trillions of trouble-free miles have been driven on how many millions of limited-slip carriers using the recommended mineral lube and additive?

 

The problem is that it's hard to know *what* to believe in todays world. Sure Eaton tells you in big letters what's *recommended*. But on the other hand they don't tell you what NOT to use and/or why not. How do we know they even bothered to test *any* synthetics at all? Saying "not reccomended", is far different than saying "recommend you do not use". One is the lack of a positive, the other is a pro-active negative. No I'm not playing semantics - they do - and that becomes our problem when searching for "the real truth or the matter".

For all we know, Eaton just doesn't want to spend the time or money to extensively test all the synthetics on the market. I can see why when they already know what works well. Since they know what's worked for almost 50 years - that's all they need to reccomend in order to save a bundle on more "silly" R&D to test for synthetic compatability.

On the other hand.. the synthetic makers *have* to test thier stuff with common rear ends including limited slip. But can we trust them with thier great claims, when ultimately they just want to sell the product?

The bottom line is that a anecdotal evidence gathered here, once filtered and compiled, is worth just as much as company claims, counterclaims, and in the case of Eaton - the lack of a claim.
I'll wager the drivers here have compiled a lot more hours "testing" synthetic gear-lube than anyone at Eaton ever did. That's why I aked my question here.. to get honest reports and opinions from people without a dog in the race at all.

-W

 

I don't know what evidence you have that the engineers at Eaton (and Dana and Auburn) haven't tested their carriers with synthetic gear lubes. All I know is, at some point, the engineers decided that the use of synthetics is a bad idea. Perhaps the recommendation followed the study of failures (warranty claims). Who knows.

But, if you wish to instead follow the advice of a few from these forums and pour a synthetic into your differential, one of three things will happen:

1) It will run great
2) It will bump and chatter
3) Limited-slip effectiveness will be reduced.

If you go with the recommendation of the engineers at Eaton (mineral gear oil and the additive) one of one thing will happen:

1) It will run great

If synthetics; ran cooler, perfomed better, extended the life of the carrier, increased change intervals, increased gas mileage (all marketing promises from the sellers of synthetics), AND reduced warranty claims, Eaton would recommend their use. But they don't. Instead, they go out of their way to tell us to not use them. Think about it.

 

Uhhh, ya you are, and you're also being pedantic. As someone who worked in the engine manufacturing business for over 30 years, part of which was writing the maintenance manuals and overhaul manuals for use by people who do not have English as their first language, you're way off base.

Almost all manufactures use standardized phrases to convey instructions using the minimum number of words.

'We do not recommend synthetic oil', or

'-IMPORTANT LUBRICANT NOTE-
The Auburn Gear limited-slip differential design has been extensively tested with high quality non-synthetic 80W90 hypoid oils treated with GM or Ford friction additives (3 oz. of additive will treat 1 quart of oil). To avoid differential clutch chatter (noise) and for optimum performance, use the oil and additive described above. Use of other additive and oil types may cause differential clutch chatter.'

are excellent examples of standard terminology. Your conspiracy theories against OEMs is insulting and displays lack of knowledge regarding common industry practice.

There again, we all enjoy episodes of 'Hold ma beer and watch this' on Youtube.

 

BS!!!

Synthetic lube with Posi additive = 1) It will run great

Period.

It WILL NOT destroy your gears!!!

 

That's pretty much all what I wanted to know.

 

Though you're quite well spoken and we appreciate your well thought out presentation backed by data, the subject of gears isn't being discussed. Please stay on topic which is "Limited-Slip Carriers". Good day!

 

Conversely by the exact same reasoning: If they had any specific data that using synthetics would be more likely to lead to *increased* warranty claims and/or a rise in complaints... they would say so forthright and *forbid* thier use in a NY minute.

And on counterpoint again... the burden of proof is on the makers of the new synthetics to do *all* the testing to prove thier stuff works as well or better than the incumbant method. Eaton can (if they wish) spend not one dime of R&D on "synthetic nonsence" and say... "we already know what works and that's what we strongly reccomend". Don't underestimate the power of "default" to set and maintain a standard. We already have a winning default standard in this case.

As for increased chatter (or conversely decreased clutch effectiveness)
that's my true and BIG area of concern. So far I've seen NO DATA as to how synthetics react with a limited slip clutch. For that matter I'm not even sure if it would "hurt" or "help" to add a bottle of the limited slip additive to a synthetic that claims to be able to do it already - and no one here has really addressed that finer point - yet.

I totally agree with you that using the same stuff that we've been using for 40+ years is the only "safe" way to go. But I still know NOTHING about the effectiveness of the newer products. The newer products claim "the moon and the stars", and Eaton on thier website hasn't shown me any test data or explained anything.

-W

 

Talk to my buddy Dave Herlinger at Corvette Repair in Mtn View, CA (close to you) but, be prepared to listen to him complain (rightfully so) about the SAD SITUATION of proper lubricants for early Corvettes in today's markets. Raj you should really call him if you need any differential or transmission work done and you live in the Bay Area. Dave did Muddy Waters Vette, My LT-1, and has many other happy customers. Corvette Repair number (650) 969-5351

 

Putting forth the theory that OEM's (like every other corporation) live and breathe for the bottom line is hardly a conspiracy theory. Like I said above - the burden of proof rests solely with the synthetic makers to prove a greater or equel status. The OEM has a 50 year history of perfection to stand on - and therefore *no financial motive* to act as a free R&D department for every yahoo with a new "gee-whiz" oil to try to sell us.

I'll go as far as to say that even if they found that the new stuff seemed to work OK - it would take a substantial increase in performance or longevity before they would greenlight a new guy. In big business it's safer to play it safe and fall back on history. And 50 years of lubricant history has defined for them what "safe" is. It's not a conspiracy theory, it's "good business" to "stick with what works" and "play it safe".

-W

 

Just to further churn the waters here, I switched to a synthetic in my 78 in the 1980's since the differential chattered and bumped with the OEM conventional fluid and I would assume the limited slip additive as the car came from the factory with 30,000 miles on the diff carrier. I changed the fluid to synthetic, bought the GM additive (which I never used and still have), and presto the chatter and bump was gone. I just changed the fluid again with Mobil 1 75W-90 and no additive a few months ago, and presto again, no chatter, no leaks, and from what I can tell, limited slip works perfectly! BTW-"we recommend" IS different than "We do not recommend" or "do not use". I still think that we do not have an answer that one is better than the other, but I certainly don't think there is ANY evidence than a synthetic will harm your differential, but the point is well taken that a conventional lubricant with the additive is certainly a safe bet that the differential will live on as long as there is nothing wrong with the diff to begin with as stated previously by me and others.

 

Exactly correct!!!!

 

Clams,..you help me make my point. Absent credible data or evidence to the contrary, why would one go against the recommendations of the engineers at Eaton (and Auburn, and Dana/Spicer, the three giants in the industry)?

Also,..

Why play chemist with synthetics and additives?

How much additive is needed with a synthetic?

If the additive is already in a quart of synthetic how do you know it's the right dose?

What data do you possess that show synthetics to be compatible with the clutches in our Eaton Posi's?

In fact, I challenge anybody to go onto the world wide web and find a credible recommendation that counters this from the Eaton engineers:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

...or something that challenges the engineers' recommendations from Auburn and Dana/Spicer which have similar verbiage in their service manauls (posted above).

Marketing materials from the sellers of synthetics would not be considered credible.

Any takers?

 

Now add this... What data do we have about the new fangled carbon-fiber clutch packs? Do they work the same?, do they like synthetics?, how much additive? ie What do we know about then except that they cost $50 more than the OEM ones?? There's no way they could have the *exact same* slip properties - so what do we use with them?

We aren't at cross purposes - I'm saying "we don't know anything about synthetics and can't rely on any companies (including Eaton) to give us real data.

I further state that in the absence of any hard data... only a preponderance of anecdotal evidence gathered *here* will help determine if synthetics are really OK - not better - just as acceptable perhaps.

-W

 

Clams,..you're smarter than that; I can tell by the way you process.

You'd rely on anectdotal evidence from a few blokes on the internet instead of the engineers at Eaton and GM, and all their R&D? I'm guessing these two groups of engineers were not at the bottom of their class.

 

I know Dave although he has not worked on my car yet. He seems really knowledgeable. I'll call him if I need any trans/rear end work done. I have a rebuilt trans and a new rear end that was put in 3 years ago. I know muddy as well.

 

I have no proof that Eaton has or has not done any long term conclusive testing of synthetics. If they had, they would iether endorse them, or forbid them. They are playing the safe ground instead, that tells me they don't have all the answers. (yet?)

Further, I have shown a financial motive for Eaton to *not* test at all and just rely on the 50 years experience to "stick with what works". Telliong people to do what they always did is safe - and free.

I have seen only claims and not tests from the synthetic makers as well - they also have a financial motive.

Therefore... considering that this is the largest gathering of Corvette owners on the web - I submit to you that statistics gathered here, from a lot more than a "few" blokes, if compiled long enough, and filtered for people with obvious agendas, would provide more raw data than iether Eaton or Mobil1 have provided us with to date.

I'm sitting here with a case of free synthetic and still debating if I want to be a guinnie pig or not. I'm pretty sure I'll use it in the tranny, it's the clutch packs that concern me is all.

-W

 

Paul74,
Yeah I know it WAS whale oil back in the day. The limited slip additive that GM sells is something else now...that is for sure. SAVE THE WHALES! I do not have the part number handy right now becasue I am not at work. BUT I do know it is the ONLY additive I use when doing rear diffs. No crap out of a tube or something somebody tries to tell me is great. Just 90w and GM's additive....that's all. But to each his/her own.

On a different note:
Heck I was once told...a long time ago...you can fill it with sawdust and throw in a few banana peels to keep things quiet......for a while. I PERSONALLY do not recommend that.
"DUB"

 

Indeed. Now it's SYNTHETIC whale oil !!

-W (I'm here all night, please tip your bartenders)

 

Raj....I purchased the drain plug kit from "Corvette Central". Look in their web site under differential drain. It works well for me and drains all the oil out of the differential when the plug is removed. Saves the hassle of trying to suck the gear oil.