73, Dark Blue 454

You (and several others above) are forgetting that there are clutches involved. Nobody is arguing against the fact that synthetics provide more lubricity. In fact, it's this lubricity that could cause issues.

From the engineers today at Eaton here:

http://www.eaton.com/Eaton/ProductsS...Differentials/

...is this:

EATON POSI

"What kind of oil should I use? Can I use synthetics? Do I need a friction additive/modifier?

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."

If you run a synthetic in your posi one of three things will happen:

1) Your gears will bump and chatter
2) Your limited slip (posi-traction) function will be reduced
3) It will run great

If you run the recommended conventional gear oil and the GM additive, one of one thing will happen:

1) It will run great

jb78L-82

Mike Ward says diffs never go bad…..

jb78L-82

I have never experienced anything but door #3 (runs great) using a synthetic and it seems there are an awful lot of folks using synthetic gear lube that also seem to be going with door #3.

I did not see any statement above from Eaton that says that you have no warranty if you run a synthetic? This argument reminds me of 20 years ago when folks did not want to run synthetic oil since they were afraid that it would void their new car warranty...

63mako

And I think the OP has a 1980-1982 Dana 44 pumpkin. Dana recommends 80W-90 Mineral Gear oil or 75W-140 synthetic.
http://www2.dana.com/pdf/CRATE44-SPEC-5-12.pdf
My 94 chevy Dually 4.11 posi recommended 80W-90 Mineral gear oil or "If subjected to heavy duty use" 75W-140 Synthetic.

lurch59

And they are bound by the Federal Trade Commission and the Magnuson-Moss Act, which states that unless they can prove the after market part (in this case gear oil) caused the failure, they are bound with the same warranty. Manufacturers can stipulate parameters or specs for the oil to be used but cannot mandate the kind of oil, and I assure you synthetics are more likely to maintain the parameters than conventional oil. Additionally Amsoil for instance, has a warranty that if the oil fell out of spec when used as recommended, they will honor the manufactures warranty.

Mike Ward

That's it?

Wow.

lurch59

You left 4 bullet points off the conventional oil argument-
2) You will have increased wear
3) You will have increased friction leading to less power and
4) Less fuel economy
5) More frequent diff oil changes.

I've used synthetic diff oil in all my cars for 10 years, no issues that the Eaton boys warn about.

73, Dark Blue 454

I'll answer by asking this simple question; how many trillions of trouble free miles have been driven on the millions Eaton posi's in the last 50 years, using the recommended conventional lube with the additive (friction modifier)?

My turn. If you're running a synthetic with your Eaton posi, have you tested your posi-traction clutches for 65 lbs of breakaway (manufacturer's spec)? Wanna bet it's less than it would be with the recommended mineral gear oil and additive?

73, Dark Blue 454

My 96 LT-4 Vette, which calls for Mobil-1 in the crankcase, calls for conventional gear oil in the Dana 44:

GM Service Manuel,..Dana 44,..1.5 quarts of 80W-90 GL-5 Gear Lubricant plus 4 oz (1 bottle) of GM additive P/N 1052358.

Dana clearly yields the lube recommendation to the car's manufucturer. Read under "Important" on page 3 of this service doc:

http://www2.dana.com/pdf/5323.pdf

lurch59

How many trillions of miles? Not nearly as many as would have been driven if they were using synthetic, and all at a greater cost both in maintenance and fuel, not to mention horsepower. I'm not saying it dinosaur oil doesn't work, just not as well.

I don't have clutches in my posi traction, I have a Tom's unit. It lays down 2 very nice black stripes, the only test I need...and of course I use synthetic.

lurch59

Of course I have more, but first you must present an acceptable argument against my premise, grasshopper.....

7t9l82

im not sure i would make the leap that reduced friction automatically translates to better fuel mileage or more horsepower, it is likely but certainly not guaranteed . i would think any difference in that area would be minimal at best. however my ring and pinions and bearings definitely had a longer life as for posi units etc i couldn't say as the car had a spool.
i have used synthetic in all my street cars since the late 70's and never had an issue.

lurch59

I will agree it's not a big difference but the amount of diff oil is minimal, therefore the upfront cost is minimal. No reason not to use it unless you are going to sell the car soon.

lurch59

It's important to remember cars are producing so much more torque and horsepower than ever before. We are no longer cruising along at the Carter mandated 55mph. We aren't generally increasing the amount of diff lube to keep it cool, so it's important to use a fluid that not only tolerates heat well, but reduces friction to reduce heat in the first place. It's just good cheap insurance.

63mako

No. Neither of those call for or spell out Conventional gear oil. Read both again.
They call for 80W-90 Mil Spec L2105-C and suitable for API Service classification GL-5 as a minimum requirement. The Amsoil I listed exceeds these specifications. I bet the Mobil 1 and Redline do as well.

http://www.amsoil.com/techservicesbu...le%20lubes.pdf

AMSOIL 80W-90 SYNTHETIC GEAR LUBE is compatible with most limited slip differentials. If limited slip differential chatter occurs, add AMSOIL Slip-Lock™ friction modifier additive.

http://www.amsoil.com/shop/by-produc...ont%2fagl.aspx

I have used this with no additives for 20 years and had absolutely no issues. When I removed my 72 pumpkin and changed the rear cover the 10 year old Amsoil 80W-90 looked brand new. The conventional I replaced looked like dirty tar.

jb78L-82

I have experienced the same in both diffs and manual transmissions with conventional gear oil-dirty tar-great description! Synthetic gear oils in the same applications look great. Again, why in the world would anyone today use a conventional oil in any number of multiple applications unless you absolutely have to ?

GeoDron82vette

Thank you all for all of the good information.

George W.

Mike Ward

Not even the manufacturers claims a temperature reduction of the magnitude that was referred to above. Of course we know that their advertising is completely unbiased.....

73, Dark Blue 454

And again, I'll answer your question with a question. Why would anybody not go with the engineers' recommendations,..engineers who design this stuff, test this stuff, study failures, oversee its production, and organize warranty programs.

And again, as stated above, the engineers at both Eaton and Dana recommend conventional lube in their limited-slip carriers. Need one more? Ok, Auburn also recommends conventional lube (non-synthetic) for their limited-slip carriers.

From here (see Q23):

http://aftermarket.auburngear.com/ma..._and_warranty/

...is this:

"We do not recommend synthetic gear oil."

So that's three sets of engineers from the three giants in the LS carrier business, all of whom recommend conventional/mineral gear oil.

There are specs called "Positraction Rotating Torque" for each car (and carrier). Here's an example of how it's tested (see photo at the bottom of this page):

http://www.gmpartswiki.com/getpage?pageid=3272

The spec for my 73 is 65-75 lbs. Anything less means that the limited-slip effectiveness is reduced indicating possible problems. The engineers know where the zone is (needed gear lube) to achieve this spec.

I've little doubt that a synthetic, with its superior lubricity, would reduce the PRT vs. the recommended conventional gear lube.

Lastly, just because it's more expensive and more modern doesn't mean it's 'more' better for our C3's. DOT-5 and Dex-Cool come to mind.

But, run whatever you want. It matters not to me. I'm simply representing the 'manufacturers' recommendations'.

73, Dark Blue 454

Mako,..the recommendations posted above for conventional gear lubes from Eaton and Dana are in plain English and unambiguous. Also see my post just above regarding Auburn's recommendation against the use of synthetics.

Regarding Dana, my 96 LT-4 Vette has the Dana 44. This is from page 7-47 of my 1996 Corvette owner's manual:

"Rear Axle (Limited Slip-Differential)

Lubricant (GM Part no. 12345977) and 4 ounces (118 ml) of Limited-Slip Differential Lubricant Additive (GM Part No. 10522358 or equivalent)."

Part Number 12345977 is an SAE 80w-90 GL-5 non-synthetic lubricant.

Also, read again, the Dana Service Maintenance guide I posted prior, page 3 under "Lubrication & Limited Slip Differentials" which clearly says to "follow the vehicle manufacturer's lubricant recommendations".