Question about axle lubricants

I recently changed out both front and rear axle lubricants, and installed Mobil One 75w90 GL5 synthetic, sealing the covers well with Permatex Black. For anyone who hasn't changed out the OEM petroleum product, be prepared for a thick, nasty, black mess when you do it. The break-in process really contaminates the lube, and I only wish I'd changed it out earlier than 15k miles. 75w140 didn't seem warranted, as I only tow occasionally, and the stuff is very expensive at $30 a qt. compared to $10/qt. for 75x90.

I didn't install the recommended 'friction modifier' as I have heard that it is not needed when using synthetic lubricant. I did a few figure-8's afterward, and I can't hear any chatter at all, in fact, it drives and sounds perfectly normal.

I've also heard that Mobil One has modifiers already added in their LS line. The bottles I bought were the old-style 75w90 style without the LS identifier. Perhaps this is a newer product in older packaging?

The question I have is this: does this friction modifier make the lubricant more, or less slippery? My guess would be less, so that locker clutches grab better, but if this were the case, wouldn't the differential make more noise if extra limited slip additive were installed?

Second question: does the addition of LS additive cause differential components to wear more quickly?

Third Question: assuming that no limited slip additive is present in this product AND the differential clutches are not chattering AND the limited-slip feature is working properly (I plan to check function the next time I lift the rear-end), is it safe to continue using this until my next lubricant change?

Incidentally, I changed out the transmission and transfer case fluid as well; both came out squeaky clean. The TC got ATF+4, the 6-sp. transmission got Royal Purple synthetic MTF.

As I understand it, synthetic 10w30 motor oil could also have been used, but I haven't heard of anyone actually using it. Safe to use, not recommended, what? (I get this information from wikipedia.com, as there is very limited information on recommended MTF types out there; some even suggest that the $35-bottle OEM fluid is nothing more than 10w30 motor oil.)

Reply to
Outatime
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In my opinion you are playing with fire by not using recommended fluids or their additives. You sure will be tossing the warranty in the trash.

The friction modifier won't hurt a normal diff, none will kill a limited slip. 'Hearing' about something, vs 'reading the directions' or the 'label' on the bottle are kinda different animals.

If a fluid 'has' an additive or 'covers' that additive, 100% for sure it will 'say' so.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I recently changed out both front and rear axle lubricants, and
Reply to
Mike Romain

I agree on sticking only with OEM-recommended fluids. The owner's manual specifies GL-5/75w90 gear lube, and Mobil One exceeds this spec. What was in contention was if the LS additive was needed if the LS unit did not chatter.

After thinking about this for a bit, I telephoned Mobil One reps this morning and got an eye-opener. It seems that I was right about the mispackaging: all of their synthetic gear lubes do indeed contain the proper amount of LS additive already, and none need be added. This explains why the differential does not chatter after the change.

He also mentioned that their website FAQ covers this:

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As explained to me, this product has always contained LS additive, but the packaging is not very clear on this, and they have recently changed it to end the confusion. Also, he mentioned that their 75w140 product also contains LS additives and that the container packaging for that will soon change as well.

The Rep mentioned that this was exactly the reason why they have always included LS additive; it won't affect normal open differentials, and that limited-slip units must have it to function correctly. This keeps them out of legal hot-water.

The exact nature of transmission lubricant remains up in the air however. The Dealership shop rep told me that engine oil or ATF can be used, that he was unsure exactly what was in the OEM bottles, and that heavier gear lube should be avoided because of cold-weather related shift problems. I haven't run into any stories of lubricant-related failures in NSG-370 units, but I suspect that is because so very few actually ever change the fluid.

So, for anyone who wants to know if Mobil One 75w90 and Mobil One LS 75w90 are the same product, it is, and that new packaging with clearer designation is already in the pipeline. Older containers will eventually be sold and be replaced by the new, updated containers, however the gear lube inside is identical.

Reply to
Outatime

I agree with Mike on this. I have heard many people say that the gear oil has the limited slip additive already added to it. I don't believe it does. On the bottles I have read it states *compatible with limited slip differentials*, which is totally different from * contains special additive for limited slip differentials *.

Reply to
Mike

Agreed; it's all in the semantics and marketing. The caviat here is that all limited slip modifiers are not of the same formulation. What works in one automakers differential may not work properly in another, and one may end up having to add more modifier to suit that application.

My Jeep guy over at Amador tells me that if the LS additive were not included, the D44 in this TJL will chatter and chirp like hell when turning, which is a dead giveaway. He also said that if you add too much friction modifier, you'll end up with a one-legger.

So far, so good. No unusual noises and the LS unit is working fine. (Jacked it up and double-checked this afternoon.) From what I've read, DC puts special synthetic 10w "break-in" gear oil in the differentials at the factory, hence the unusually frequent gear oil change schedule. Who knows. Accurate information is hard to come by these days.

Reply to
Outatime

I second what the Jeep guy said. A LSD chatters like all get out if it doesn't have friction modifier in it. I put some synthetic in both axle differentials in my Jeep once I figured out it was going to be a cold winter. Already had something in the transmission. 5W30 in the engine too.

Earle

Reply to
Earle Horton

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