Let's talk Vari-Lock ( Jeep Quadra-Drive )

[shovel]

Like the subject says, let's talk about Varilock differentials as equipped in Jeep WJ's:

First axles:

• Is pump behavior, friction material, etc supposed to be the same for both D30 (front) and D44A (rear) devices?
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  And viscisity:
  • How does viscosity affect behavior? Will a thicker oil promote engagement earlier because it doesn't bleed out of the reliefs?
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  And lubricant properties:
  • How are the clutches affected by dino vs. synthetic?
  • Is the use of more or less Friction Modifier than prescribed detrimental to clutch lifetime or is it strictly a behavior/road manners correction?
  • My understanding is the transfer case's power split device works in the same way as the differentials', with a gerotor pump and a stack of clutches. The transfer case is (reportedly) picky about lubricant - requiring only Mopar 05016796AA or Mobil #424 fluid. I know this is a much thinner viscosity than 75W140 but would there be some other magic fluid in Mobil's (or anyone's) commercial lubricants catalog that can offer improved behavior in Varilock differentials?

 

[shovel]

To start with my own experience, I picked up a 2002 WJ with Quadra-Drive earlier this year, ~112k miles and didn't seem to have been abused or ever used off-highway. I didn't choose to operate it in rough terrain (and there isn't really any snow around Phoenix) until after my first fluid changes, so I don't know how it behaved with whatever fluids were in it when I bought it.

At my earliest convenience, I drained both differentials and cleaned them with brake parts cleaner, rags and compressed air until I felt satisfied they were quite spotless, and refilled with Mobil 1 Synthetic 75w140, which claims to not require additional friction modifier so I did not add any.

Upon driving off-highway, I found myself a little frustrated in the behavior of the differentials - notably they just acted like open carriers. When I had the luxury of driving into a sand "V" ditch to practice bringing the differentials to engagement under safe and controlled conditions, it appeared that under heavy throttle the differentials would behave as open diffs until a significant amount of speed built up, then clamp firmly and instantly, then let go almost as quickly after the stopped wheel began turning. I was able to repeatably drive out of the "V" ditch, but there was nothing elegant about it.

This bothered me, and I did about the only thing I could think of to learn how Varilocks should behave - watched Youtube videos. Those reinforced in my mind that mine weren't working as they should. A close friend who is a Mitsubishi Montero enthusiast told me that they "found out the hard way" that synthetic oil renders their (spring preload operated) limited slip differentials useless, and all they run is dino oil with no friction modifier.

OK, my next step was draining the differentials and filling with Valvoline DuraBlend (blended synthetic/conventional) 85w140, still no additional friction modifier as the oil claims to be compatible - which made an enormous difference in behavior. Much earlier engagement and much smoother engagement, though I still wouldn't call it elegant.

 

[shovel]

So -

What do we think is the ideal lubricant for these differentials then, to provide gradual but effective lock-up?

Dino oil with a dash of Mopar FM? Thicker or thinner oil? Some specific commercial lubricant?