To use or NOT to use 75-90 Limited Slip GL5 gear oil...that IS the question!!

[seafish]

I am getting ready to service front and rear differentials on my 2005 2500 as well as change diff covers to higher capacity MagHytech front and rear. In short, I need almost THREE GALLONS (12 quarts) of GL5 75w-90 lube, but I am having trouble finding it WITHOUT friction modifiers added in already. I also seem to recall that one should NOT use LS additives in a Torsen type LSD like the AAM 11.5 has.

So should I use this Castrol Syntek GL5 75w-90 gear lube with NO friction modifiers?

https://www.amazon.com/dp/B00B9XDRB...UTF8&colid=335F90LP4L51B&coliid=IKSQY31RZZVSN

Or get a MUCH more affordable Mobil1 75-90 LS --

https://www.amazon.com/Mobil-104361...8&qid=1475901450&sr=1-1&keywords=mobil1+75-90

In short, are you guys using the GL5 75w-90 differential/axle lube WITH or WITHOUT limited slip additives??

 

[Killer223]

no modifiers needed on the AAM axles. they are NOT clutch type difs.
i use walmart supertech oil and it's been fine for a combined 390K on both my trucks.

 

[seafish]

I understand that no friction modifiers are needed with the AAM axles on our trucks, but what I would like to know with more certainty if a gear oil with LS additvies will be detrimental to the operation of the differential like some suggest.

 

[Killer223]

no, they will not harm the dif.

 

[Prairie Dog]

no, they will not harm the dif.

ditto - no harm at all,

 

[cerberusiam]

no, they will not harm the dif.

Uh uh, not so fast. The additives for clutch types LS's is not a good idea. They are formulated to work on a number of large surface area clutches, the surface area on the LS brake shoes is a lot smaller. ANYTING that modifies the braking effect has the potential to mess up the operation. The operation is already marginal with the TQ of the ISB, don't really want to mess with that too much.

 

[Killer223]

most of the time i agree with you Cerb, but this is one of those were i can't.
the gear operation of these difs are not even close to the older clutch type.
you might be right. but i might not be wrong.. unless i have definitive proof. i'll not worry about it.

 

[seafish]

My AAM 11.5 diff has always operated well for me, unl;ike some other peoples who seem to think theirs don't grab well and it has NEVER had lube with friction modifiers in it, so I guess I won;t start using it now, particluarly since I found the local Oreillys MasterPro GL5 75w-90 has no additves in it and was quite inexpensive. I bought TWELVE quarts of it and should be good to go for another 30k.

Thanks for the input guys and do feel free to keep talking about it in this thread!!!

 

[GCroyle]

seafish,

Any chance to ask Mobil via "contact us" and ask them the question?

I think a valid question but answers like this need citations for the answer.

Storm gone clear skies and LOW humidity!

Gary

 

[cerberusiam]

the gear operation of these difs are not even close to the older clutch type.

Yes, the operations are different. That is not the question though, it is the formulation of lubricants that is the question.

Additives meant for clutch type LS's work by making the less harsh when it moves, it allows a managed slip of the clutches without the harsh grab or release, the normal state is both axles locked.

The AAM LS unit works opposite, it doesn't slip to make the LS work, it grabs. An AAM LS's normal state is axles unlocked. They rotate at differing speeds with no issues under low TQ input. TQ activates them hence the TQ Bias moniker. When one axles exceeds the speed of the other the gear system attempts to slow the speeding axle by applying a braking force to shift the bias to the other axle. This is done thru a set composite brake shoes on side gears.

Since the AAM LS is not trying to make that interface 100%, or 0% bias, the efficacy of the braking is not high enough to overcome ANY additive that modifies the friction. The brake shoes are not large enough to really grab hard like a multi-clutch pack, they just attempt to slow the axle somewhat. Drive still has to use throttle input to balance the effect, unlike a clutch type.

As a rule, the AAM LS will not chatter and make noise in a powered turn and it is fairly effective at keeping TQ to each axle balanced with some operator input. When they start chattering on turns or not working at all in low traction situations there is a problem. That problem could be a simple as the wrong fluid. The additives can soak into compounds not meant to resist them and permanently modifying the compounds operation.

Just like oil soaking a clutch disk or brake disk\shoe it never works the same after the fact. There is almost no information on the braking shoes and I don't they are even available as a separate item, the AAM LS is sold as a complete unit and as a rule is not serviceable. Using fluids not meant for it, or with comparable ratings, is taking a chance it might not work as planned. It is definitely not a given LS additives will hurt it, on the flip side there is no guarantee using non-recommended fluid will NOT cause problems either. Official word is additives are not needed or recommended, you will never get an iron clad yay\nay to potential damage issues.

Fight the battles that can be won, this isn't one of them.

 

[seafish]

^^^^ VERY well said.

 

[Prairie Dog]

My LSD has always worked great and I've always used the fluids that advertise they are for clutch type diffs.
YMMV.

 

[mwilson]

Just doing several Mobil orders and this thread came to mind. According to my spreadsheet the Mobil 1 synthetic 75W90 is LS, whether packaged in quarts or 5 gal pails. Material number for the Mobil 1 75W-90 quarts is 104361 and Customer Part number is 98W573.

Now if you go to Mobil Delvac then non-LS synthetic gear oil s available in both 75W-90 and 80W-140.

Quart Packaging 75W-90 Delvac Synthetic

Material Number is 120269. Customer Part # 98HL97.


80W-140 Mobil Delvac Synthetic is not offered in quarts, smallest packaging is a 5 gal (35lb) pail.

Material Number is 105451. Customer Part # 98HL84.

These part numbers may change as Mobil is streamlining some numbers but what I have provided will get you where you need to be.

Apparently they figure that the Mobil 1 LS will cover the automotive market with a single product.

Hope this helps.
Mike.

 

[jdross440]

Call Pat Angst at AAM. He is in Tech Support. 313-758-4716. I have talked to him recently about a vibration problem and also lubes. He said synthetic is not necessary. The 4wd shop had chgd my gears and put in non synthetic oil. I had chatter bad so they put in 2 bottles of LS additive and that stopped it. Before this I was using Mobile 1 that had LS additive with no problems in 50k miles.

 

[BLNRAY]

Mobil 1 ,75W-90 for 423,000 mi.,don't know what's in it but it seems to be good stuff.