What gear oil to use for new gears and LSD?

[DarkoNova]

I was told to use something with GL-6 and then add a limited slip additive. So what's the recommended oil? Are there any oils that already have the limited slip additive in them?

[big gear head]

Use any good 80W90 gear oil and the GM oil additive. I'm told that the GM additive has been discontinued, but the Ford additive is still available. If you can't find the GM additive then use the Ford additive. Don't use any additive that starts with the letter K, comes in a tube or any auto parts store additive.

[DynoDon]

I run Lucas Synthetic or Mobil One Synthetic GL6 with Ford friction modifier.

[DarkoNova]

Can I get the Ford friction modifier at a parts store or do I have to go to a Ford dealer?

Also, I found a couple bottles of Royal Purple Max-Gear in my garage. I used it in my 88 BMW and never had a problem with it, but that also has 150k miles, so I don't know how it would compare to breaking in a brand new ring and pinion. It says it has a friction modifier in it. One of the bottles is about half empty, though, so regardless, I'll have to buy at least one bottle.

[big gear head]

You will have to get the Ford additive at a Ford dealer. I would just use regular 80W90 and the additive.

[DarkoNova]

K, I'll just get some oil at Ford when I get the friction modifier. You think one bottle of friction modifier will be enough?

[big gear head]

Yes, one bottle is enough. If you use too much the clutches will slip too easy and you will be spinning one wheel again.

[DynoDon]

Some parts stores stock the Ford Friction Modifier. Call around

[DarkoNova]

So my dad picked up some oil for me over the weekend. I told him GL-5 fluid and a bottle of Ford friction modifier. He bought 3 quarts of Valvoline Synthetic 80w-90 limited slip gear oil and a bottle of Sta-Lube Equa-Torque Differential Friction Modifier.

Are those good oils or should I take them back?

[big gear head]

The oil will be fine, but the additive isn't any good.

If the oil is suppose to have additive in it then try using the oil without adding the Ford additive for now. Drive it for a little while and see if the posi pops or jerks when you turn tight corners. If it does then add a little of the additive, but not all of it. You want just enough additive to keep it from popping and jerking, but not too much. If you use too much then the clutches might slip when you don't want them to, like when you are doing a burnout.

[JEFFTATE]

The GM additive is GM part #1052358 . It is still available.

I've always been told ( by several people on here ) to use a petroleum ( old school ) fluid with the old Eaton (clutch style) positraction units. Then add a bottle of limited slip axle additive to it.

But , you can use synthetive lubricant with later units that have different types of posi units or clutches made of newer type materials.

I use Torco Brand RGO 85/140 in my Camaro with a bottle of the GM additive.

I can't say it better than member ]"Chicane67" ,

"If you are using a late model EATON posi... you shouldn't use a synthetic.

If you are using a steel plate clutch pack, like that found in the OE posi... you can. However... I dont recommend using a synthetic in the differential at all. I would look for a good parafin base oil like that from Schaffers (#209 moly) or TORCO (RGO 85-140.)

For your climate, you can run a multi viscosity 85-140, or either a straight weight 90 or straight weight 140.

At this point... all you need to do is add about four ounces of friction modifier to the base oil that you are currently running. It can be had from your local GM parts dealer or your local Ford parts dealer. "

I have tried and used just about every oil that has been on the market in the last 20+ years.... and with specific use of the Eaton limited slip, (both OE circa middle 60's and the late model units (there is a big difference between the two)). But, there is no reason that you could not use a full synthetic lube with the older, solid steel clutch pack units or the newer laminant/fiberous clutch packs. The newer clutch packs however can be a little sensitive to the amount, or lack of, a friction modifier. Some syn's even have their own fric mod built into the base oil. For reference, the better syn's with an intergral fric mod are Torco, Amsoil and LE. All of which I would recommend for use with an Eaton limited slip...... but remember, a new or tuned posi may require more fric mod to operate without clutch chatter. NOT ALL synethics are created equal..... and I wont run synthetic in a differential unless it is from one of the manufactures I listed above.... **for street use**. In a race car, where the differential lube will be changed more than your underwear, I might even consider a product or two from RedLine..... but in my opinion, even their differential products are too thin and dont have the film pressure strength for use in a hypoid gear assembly. And I definately wouldnt use it in a street car........

The best thing I have found for use with an Eaton limited slip differential, in a non-syn, is a parafin based oil from Schaffer. It still requires an additional friction modifier and my first choice of that would be the old Ford friction modifier (which I dont think is even available anymore), but it too is parafin based and mixes well.

Now, as for a NON Synthetic, I have been using Schaffer strait weights with a suspended moly in differentials for near 16 years without any oil related failure or brakedown. This includes differentials in Land speed record events, Top Fuel D+F/C, Pro Stock, Trophy Trucks, SCCA Trans-Am, IMSA..... Ambulances and Fire trucks..... street cars etc etc. If you are/were directed to use a non-syn lube, I would highly recommend the lubericants from this company.

For normal every day street cars I use a strait 140wt and an additional 4oz bottle friction modifier. Sometimes more, sometimes less.... but on an average, 4oz will do just fine. Some times, you will need to drive the car around for a while, so that the oil and friction modifier has a chance to work into the clutch packs....

If you run a full synthetic, run something with quality. I have even heard from some Eaton engineers, off the record, they dont have any problems with Torco or Amsoil..... just keep a bottle of friction modifier handy if you have to add an additional ounce or two in case you experience clutch chatter[/B].

[big gear head]

The new Eaton Posi has carbon fiber clutches in it. These are the same clutches that are used in the '99 and later GM trucks with the Eaton Governor Lock, and every one of those trucks comes from the factory with synthetic oil in them. I've been using Amsoil in rear ends with old and new Eaton Posis for over 13 years (probably a few hundred rear ends) and I haven't had a problem with one of them.

[MonzaRacer]

Do not rebuild a rear diff with new gears and use synthetic first off, the gears wont mate and you will have noise and other issues.
Besides a fresh build you need to use good dino oil, i always recommend 85w140 and there are several good friction modifiers and as for the Kendall stuff ,,guess who make Ford and GMs, just so you know.
BUT generally the Ford and GM are more concentrated so as to fit in smaller area and allow more fluid.
I have used Lube Guard with good results as any and its available at Carquest. I have also used others.
When breaking in new gears, use non synthetic oil, 85w140 Shell Spirax/Rotella gear oil from Wal-Mart works great and limited slip additive, drive approximately 50 miles at no faster than 50-55mph, vary your speed some. Dont hold steady speeds. Then park and let rear end and lube cool off. Figure 2 to 4 hrs depending on outside temp. Take in a movie and long lunch, drive back home.
Drain it completely. Then refill again with 85w140 and LS additive, note mileage and leave oil in about 500 miles, and then service again.
Now your diff is ready for proper use. During breaking be warry of beating on it till gears are seated in good. Figure at least half way through the 500mile service.But I recommend going full 500miles first.
Gears are just like engine bearings they are work hardening during use and if you beat on them too soon you can damage them. OH and after the break in during the 500 mile rune you need to watch fluid leve las distillates of the LS additive will boil off and you can actually add more gear oil.
Me I measure amount of gear oil I install, then divide up the LS additive and add it some to all my bottles.
After getting about 10k miles you can switch to synthetic and synth doesnt need LS additives and Mobile 1 is my favorite Synth lube.

[DarkoNova]

Yeah, my posi came with a little paper that says "it is strongly recommended the Eaton Posi LSD you have purchased be installed using a Mineral Based 80W90 Gear Oil (GM# 1052271) and a 4 oz. bottle of Limited Slip Additive (GM# 1052358)."

I'm kinda worried about using the synthetic oil now.

This all just sounds like such a hassle. Synthetic vs non-synthetic, having to have the perfect amount of friction modifier...maybe I should have just kept the open differential LOL.

[Yoda4561]

They also split the gear oil grades recently, The old 90 is now split into 90 and 110, and the old 140 is split into 140 and 190. Same range of viscosities but now split into 4 grades instead of 2. For break-in any should work (80w90 shouldn't be in there long enough to shear out of grade), but for any heavy duty use I'd lean towards the 140 weight oils. 75-110 oils should be good for general duty or anything recommending an older 90w oil. http://www.lubrizol.com/J306.aspx?id=33216&terms=J306 I wouldn't use a newer 80w90 oil regularly unless I had an open differential or was trying to get best mpg in an economy car .

edit:: Okay, been a while since I actually read up on all that sae J306 stuff, it was changed in 2006, so any oil on the shelf now should probably be using the new specs.