"Rear Axle Differential Temp Increased, Decrease Speed" warning

[steveespo]

Which means time to change your oil ;)

Already have 5 liters of Miller Oils 75W90NT, will do tomorrow. Miller Oils are fully PAO ester based sythetics and have proven to me in my other road race Mustang to reduce temps 10-15 Deg F. May be enough to keep the warning flag down until I can build a cooler setup.
Steve

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[GT_Roadcourse_Newb]

Already have 5 liters of Miller Oils 75W90NT, will do tomorrow. Miller Oils are fully PAO ester based sythetics and have proven to me in my other road race Mustang to reduce temps 10-15 Deg F. May be enough to keep the warning flag down until I can build a cooler setup.
Steve

If I understand things, we have an interesting matchup here.

75/90 hoping to keep it cool
or
75/110 hoping to keep the oil from losing its worth

 

[steveespo]

If I understand things, we have an interesting matchup here.

75/90 hoping to keep it cool
or
75/110 hoping to keep the oil from losing its worth

I am running the 75W90 only because that is close to the factory weight of 75/85. This is the spec oil for both the 5.0 and the GT350s. I spoke with the GT350 program manager and one of the GT350 drivetrain engineers and they said running heavier lube will only add drag to the gear set, no improvement in protection. They also said that the factory fill has friction modifier in the Torsens. Shop manuals support this information.
Steve

 

[Bahndvr]

I am running the 75W90 only because that is close to the factory weight of 75/85. This is the spec oil for both the 5.0 and the GT350s. I spoke with the GT350 program manager and one of the GT350 drivetrain engineers and they said running heavier lube will only add drag to the gear set, no improvement in protection. They also said that the factory fill has friction modifier in the Torsens. Shop manuals support this information.
Steve

Why would you (not you specifically) use friction modifier if the Torsen diff uses helical gears?
It's well known that friction modifier doesn't let the oil cool as well as no friction modifier.

 

[GT_Roadcourse_Newb]

I am running the 75W90 only because that is close to the factory weight of 75/85. This is the spec oil for both the 5.0 and the GT350s. I spoke with the GT350 program manager and one of the GT350 drivetrain engineers and they said running heavier lube will only add drag to the gear set, no improvement in protection. They also said that the factory fill has friction modifier in the Torsens. Shop manuals support this information.
Steve

I thought there was relative consensus that 110 weight oil was good. Maybe I'll try that stuff when I replace next.

Still, seems possible to me that the heavier weight oil would fare better through a few warning messages over a few track days, no?

 

[Optimum Performance]

Why would you (not you specifically) use friction modifier if the Torsen diff uses helical gears?
It's well known that friction modifier doesn't let the oil cool as well as no friction modifier.

Never heard that before, care to explain? It's a simple additive.

 

[steveespo]

Never heard that before, care to explain? It's a simple additive.

Never heard that either. I am just following the service manual for 2016.
I have run Torsens with and without the friction modifier. The Super 8.8 is new to me so just following the rules.

 

[EXP Jawa]

Helical gear diffs don't have clutches, but sometimes they can squeak or "moan" under low load conditions. It's a friction noise, and friction modifier eliminates it. So Ford adds the modifier to reduce the chance of a warranty complaint for a part that's otherwise working correctly.

The other thing the FM does with a Torsen differential is that it lowers the torque bias ratio somewhat. By running without it, you can potentially enhance the diff's lock-up characteristics. That may, however, be offset by using slippery aftermarket synthetics. A synth 75W140 will be slipperier than the OEM 75W85 fill, so would have a negative impact on TBR as well. The two may cancel each other...

 

[Norm Peterson]

I wonder if that means you could improve the bias by flushing the factory fill and replacing it with a weaker concentration of FM that still eliminates all or most of the noise. Even if you intentionally start too weak and keep adding a little at a time until you're happy.


Norm

 

[EXP Jawa]

Maybe, but in my experience, whether you put 2 oz in or 4 oz, it isn't a marked difference with regards to TBR. There's more difference between no modifier and a small amount than there is between smaller and greater amounts. At least within the scope of the volumes we're talking about here. That would be different if you, say, added a significant % of the fill as modifier. But you wouldn't do that.

However, I do have reliable data that shows when oil w/modifier is flushed and replaced with unmodified lube, the TBR comes right back up again to where it would be prior to adding the modifier. So, at least its easy to reset.

With all that said, the squeaking doesn't exhibit in every axle in every car. Its a bit dependent on the noise path from the axle to the cabin, so it probably would be more prevalent if firmer subframe or carrier bushings were installed. But still, it really only presents when in a low speed, tight circle. If you spend a lot of time driving in a full-lock circle at 1000 RPM, you're more likely to hear it. But a lot of drivers never would in their normal operation of the car.

 

[Bahndvr]

Thanks EXP Jawa for jumping in. I don't know the technical language.

The friction modifier (anti-wear agent) thing has been hashed out over 10 years ago and I'm think of the 03/04 Cobras. They were originally clutch IRS and guys were putting in helical gears (TruTrac or what ever). So the question would come up about FM.

 

[Optimum Performance]

Rick, that is some great information, we can get BG rear axle lube with out the additive. Same stuff just not LS on the bottle. I'm wondering if it would make a noticeable difference on track with the Torsen. If I understand you correctly it would take more to "unlock" it with regular (non-additive) fluid possibly giving more equal torque to the drive wheels on corner exit?

 

[EXP Jawa]

That's sort of it. Torque Bias Ratio (TBR), also called Locking Effect, is a term used to quantify how much resistance to wheel spin a differential has. This is true of really any type of LSD, plate or helical. These things work by creating internal friction; friction in the diff is what allows it resist wheel spin. By the same token, that resistance is also what allows a differential of the non-open variety to distribute more torque to the side that can best use it. The higher the TBR setting is, the resistance there is the start of slippage, and the more torque it can send to whichever tire has better traction. In essence, by building resistance to spin, the differential can hold the lower traction back from spinning, which allows the higher traction wheel make use of more torque.

The level friction that the differential develops is different, depending on if the parts are static or if differentiation is taking place. Think of trying to push a crate across a floor - you need more force to get it to move initially than you need to keep it moving. The coefficient of friction is higher when things are static compared when sliding. So, there is more resistance to wheelspin when the diff gearing is not moving inside the case, which is what happens when driving in a straight line. But when you turn, and one wheel speeds up while the other slows down, the diff gears what to move. Once enough force is on the axle shafts to overcome the differential friction, then they start to move. In doing that, the amount of friction generated is reduced. Again, this is all true for clutches as well as helical gears.

Now, that transition from static to dynamic is often kind of abrupt; torque gets wound into the gearing until the friction is overcome, and it pops free and moves. But when it does that, the movement slows and the coefficient goes up, and so it stops moving. At least, until the friction is again overcome and it pops free. In that transition, sometimes you get that stick/slip/stick/slip going on a lot. This stick/slip is what causes clutch plates to chatter. Its also what causes a helical diff to squeak.

Bringing this all around again to friction modifier - the actual function of modifier, the "modification" in makes to the friction, is that it brings the static coefficient of friction down to a similar level to the dynamic coefficient. It helps smooth out the transition from static to dynamic and largely eliminates the chatter or squeak that results. But it does this at the price of lowering the overall coefficient of friction for the whole system.

Looping back to the differential being a friction device; the friction it generates is directly influenced by the lubricity of the oil blend in the system. So, if the oil's friction properties are reduced, the amount of friction - and thus, TBR - the diff produces is proportionally reduced.

So, sorry about the long winded answer. But, yes, the locking effect properties of the differential will be increased by running oil without modifier - but only if that oil is otherwise comparable to the properties of the original base oil. If you replace higher friction base oil w/modifier with a lower friction oil that is unmodified, there may be no net change.

 

[NvrFinished]

Bringing this all around again to friction modifier - the actual function of modifier, the "modification" in makes to the friction, is that it brings the static coefficient of friction down to a similar level to the dynamic coefficient. It helps smooth out the transition from static to dynamic and largely eliminates the chatter or squeak that results. But it does this at the price of lowering the overall coefficient of friction for the whole system.

This smoothing out from static to dynamic would require more consistent movement or slipping than the stick/slip/stick/slip you are referring to, would it not? Is the more consistent slipping, which builds heat, the reason why the fluid is getting hotter in the road course environment?

 

[GT_Roadcourse_Newb]

I got the axle temp warning one time today at Thunderhill. It was unseasonably cool.
I predict many message popups when driving hard in 105 degree weather.

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