Synthetic oil in Traditional oil differential

[zeng]

I am with Strange/East Coast Gear/ Lucas and such , on their recommendations of mineral 85W140 oils in heavy duty differential applications .

It's about components protection < oil film thickness < operating viscosity/pressure-viscosity coefficient among others .

 

[reddevil]

Gears, engine are machines etc are metals that interact with the physical properties of the oil/fluid. If a fluid has the exact physical specification, the machine cannot tell the difference between synthetic/mineral oil. In fact the first minute when the oil is added, both mineral/synthetic behave the same(with same spec). But over time, the additives and base oil between synthetic and mineral begins to difference themselves. Additives and better base oil makes the oil retain the physical properties longer.

 

[MolaKule]

I am with Strange/East Coast Gear/ Lucas and such , on their recommendations of mineral 85W140 oils in heavy duty differential applications...

Why NOT 75W140 instead of 75W90. Eaton's torque sensing differential specifies Synthetic OR Conventional 75W90/80W90 gear lubes and operates on the same principle.

...< oil film thickness < operating viscosity/pressure-viscosity coefficient among others .

Please explain how any of those factors would affect the theory of torque sensing .

 

[Asterix]

The voiding warranty bit is stupid. However, helical gear LSDs are sensitive to friction between the inner gear shafts and case. I could see LSD friction modifier (which reduces it) would affect how this LSD works. I'd ask for more details from Strange as to exactly why they spec what they do, and back it up with performance data.

 

[AJB0009]

Listen, I know that we here at BITOG love to overthink things; it's what we do.
In this case, I'm guessing that this unit was pretty high dollar?
I would not waste what few brain cells that I have left thinking about this. I would dump in exactly what they recommend and not think twice about it. I would have the warranty coverage if anything ever did go wrong (but don't worry, it won't; it will be just fine.).
My $.02

 

[4WD]

Listen, I know that we here at BITOG love to overthink things; it's what we do.
In this case, I'm guessing that this unit was pretty high dollar?
I would not waste what few brain cells that I have left thinking about this. I would dump in exactly what they recommend and not think twice about it. I would have the warranty coverage if anything ever did go wrong (but don't worry, it won't; it will be just fine.).
My $.02

Well … another thing when using conventional is to make the fluid change easy by having the drain and fill easy to do with top and bottom (magnetic) plugs. If it’s not built in … an aftermarket cover can help.

 

[DGXR]

Listen, I know that we here at BITOG love to overthink things; it's what we do.
In this case, I'm guessing that this unit was pretty high dollar?
I would not waste what few brain cells that I have left thinking about this. I would dump in exactly what they recommend and not think twice about it. I would have the warranty coverage if anything ever did go wrong (but don't worry, it won't; it will be just fine.).
My $.02

I agree. But also I am curious about the reason behind the conventional requirement. If the viscosity is the same, why does it makes any difference? If anything, wouldn't synthetic last longer in this EP shearing environment?
OP, what does Strange say about the service interval for your new differential set? If it's insanely short (20k miles or less), that might help to explain a few things.

 

[ABN_CBT_ENGR]

BUT what is the engineering reason? Is there an actual technical reason?

Yes there is and I'm sure its proprietary but I have seen this before on industrial gearing of "similar" design. ( Not a textbook Torsen per the patent but along the same lines)

They utilize a baked on dry lubricant ( I suspect moly but could be CF) on thrust surfaces (per their advertisement) for a COF enhancer.

They also state they use a heavier geometry with a factory preload. ( which would justify the coating and even the cold treatment)

If that's how they are regulating the bias then that's most likely why they don't want any additional FM's to alter that.

That's a guess, granted, but an educated one based on similar situations not automotive in nature.

 

[MolaKule]

Travis4x4 - Yes follow their recommendation.

BUT what is the engineering reason? Is there an actual technical reason?

WE are left hanging. No coconut filling in the coconut bun. Just tissue stuffing. No creme in the Twinkie. No cash in the account.

Travis4x4 - please can you ask Strange why EXACTLY??? In detail. Thank you.

From Strange's website:
Dry Film Solid Lubricant Coating
• Applied to thrust surfaces
• Minimizes component wear

My interpretation is this coating is applied to reduce both run-in and further operational wear of the thrust surfaces.

Gear oil formulations, whether synthetic or conventional, contain a mixture of Group II to Group V base oils. Synthetic gear oils simply contain a higher level of Group III to Group V components. The additive packages of both contain EP chemistry, metal inhibitors, rust inhibitors, VII's, emulsifiers, surfactants, and friction modifiers.

Without a definitive engineering or chemical effects response (technical reason) from Strange, we are still left with the question: What is the mechanical or chemical explanation is there for the choice of conventional lube over a synthetic lube?

 

[RDY4WAR]

It makes me think of old timers who say you can't run synthetic in a GM 10 bolt, stock G80 diff because it's "too slippery."

 

[OVERKILL]

It makes me think of old timers who say you can't run synthetic in a GM 10 bolt, stock G80 diff because it's "too slippery."

Indeed. And any OEM who implored me to run a Lucas product would be sufficient grounds to seek out a different OEM. If you've married yourself to the snake, I don't want to even consider what other slimy goings on are in play.

 

[Scuder]

From Eaton's webpage. Maybe it can be inferred that some of the same applies to Strange Axle's product:

What kind of oil should I use for my Detroit Truetrac? Can I use synthetic? Do I need friction additive/modifier?

• A quality, petroleum-mineral based, GL5 rated 80w-90 gear oil should be used.
• Synthetic oils are not recommended for Truetrac applications. While some customers have found that synthetic oils works well in this application, Eaton has not confirmed under test conditions that all synthetic oils are compatible with Detroit Truetrac applications.
• Friction modifiers should not be used because they will decrease performance (reduce differential bias).

My friend has an '80s vintage Gleason Torsen in the Dana 60 in his 1970 'Cuda 440. I think it required different axles, as its intended application was a Ford truck Dana 60 with different splines. As of a couple years ago, it had the original Pennzoil 4092 (80W-90, non-LS) he used to first fill it 30+ years ago. Granted, it's not a high use vehicle anymore.

 

[MolaKule]

See this video and notice the discussion of fluid choices at about 4:50

https://www.summitracing.com/parts/DTL-913A614/media/video

 

[zeng]

My understanding is it’s recommended for certain applications such as hypoid, spur, bevel, helical, spiral-bevel and worm gears in differentials.

As to why I still don’t know. 💩

Synthetics typically out perform mineral (conventional) oils.

Mind checking with OEM/Strange if the (low) pitch line velocity of the helical gear teeth pair/set within has an influence on their recommendation , other than typical velocity of pinion/ring gear set .
Back up with rejection/failure data (in warranty claims application) between mineral/synthetic options ?

 

[bogito]

edited

 

[bogito]

See this video and notice the discussion of fluid choices at about 4:50

https://www.summitracing.com/parts/DTL-913A614/media/video

I was wondering where 4.50 was on the 1 minute video, but then realized there is a second video on the bottom. Thanks, it was helpful.

 

[Kira]

Could it be that that FM's are so often included in synthetic gear lubes that the manufacturer specced "FM-free" conventionals simply to avoid FM's.

Not having customers contacting them about "FM-free" synthetics saves them a lot of time.

 

[SoNic67]

I assume that the mineral requirement comes from the actual friction that's required to properly function. Lower friction will adversely affect it. That's why LSD compatibility or modifiers will affect it.
Most if the synthetic lubricants are listed as LSD compatible because of natural lower friction of synthetic oils.
So probably that's why they said no synthetic, just to be on safe side of their warranty.

 

[MolaKule]

Could it be that that FM's are so often included in synthetic gear lubes that the manufacturer specced "FM-free" conventionals simply to avoid FM's.

Not having customers contacting them about "FM-free" synthetics saves them a lot of time.

That's a good question and it seems there is still some confusion about FM's in gear Lubricants.

Speaking to differentials and differential lubes only, there are Friction Modifiers in BOTH Mineral Oil-based and Synthetic Oil-based gear lubricants, which is there for the sole purpose of reducing friction between both gear teeth and in bearings, and the effect of this additive component is to increase gas mileage and to lower diffy temps.

There is a special purpose Friction Modifier chemistry for Limited slip (LS) differentials (Non- torque-sensing types) with cone or flate-plate clutches whose sole purpose is to prevent chatter and vibration when attempting to lock-up or disengage. So the gear lubricants with LS modifiers will have both types of Friction Modifiers contained therein, whether the differential Gear Lubricant is conventional (mineral oil-based) or claimed as fully synthetic.

Gear lubes claiming to be mineral oil gear lubes only have synthetic components (synthetic chemistries) in them.

Both the Strange differential and Detroit Truetrac differentials are working on the same principle of sensed reaction forces for management of torque transfer.

So as for me, I am still dubious of the requirement for a mineral only differential fluid when the Detroit Truetrac differential manufacturer plainly states I can use either a Mineral or Synthetic GL-5 differential lube.