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I used the Royal Purple gear oil with no additive.
I don't think such a thing exists. They make one 75w90 and it clearly says it contains additive.

However, you have a ZR2 so you don't have a G80 and your lockers don't care if there's an additive in the gear oil.


"Formulated with a friction modifier additive, therefore no additional additives are necessary."

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Cannot go wrong with the GM/AC Delco gear oil, if it was not good, the factory would not use it.
 
Cannot go wrong with the GM/A C Delco gear oil, if it was not good, the factory would not use it.
As long as it doesn't say "LS" on the bottle then sure, you can't go wrong. :D There is this which shouldn't be used...
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I don't think such a thing exists. They make one 75w90 and it clearly says it contains additive.

However, you have a ZR2 so you don't have a G80 and your lockers don't care if there's an additive in the gear oil.


"Formulated with a friction modifier additive, therefore no additional additives are necessary."

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If I'm understanding, this is fine in a ZR2?

Amazon.com: Mobil1 1043611 Full Synthetic Gear Lubricant, 75W-90 Quart 6 PK : Automotive
 
Either will be fine it....
The one thing that is said is not to use Limited Slip Additive.

I have used with Limited Slip Additive in mine.. and have had no issues.

But either Delco GM synthetic 75-90 or Mobil 1 and you will be good
It doesn’t really matter. Most modern synthetic gear oils have barely any additive.

Just don’t add any more.
I can see how someone could easily become confused about this, since the Eaton MLocker (G80) uses friction discs to lock both axles together.

While it does share that clutch pack design and functionality with certain clutch-type Limited Slip Differentials, the similarities pretty much stop there because LSD's never truly lock the axles together unless both wheels or axles are spinning at the same rate. Instead they transfer torque to the wheel or axle with the most resistance, and allow the other to slip. The G80 works in almost the exact opposite way because it locks both axles together when the axle spin differs by approximately 100 RPM.

LS additives are friction modifiers that allow the clutch plates or gears in an LSD to slip more freely without chattering. This is detrimental to the G80 because its clutches aren't designed to slip when it engages.

So in reality, it absolutely does matter.

Not to mention that GM has published numerous TSB's recommending against adding LS additives to the G80 for decades now...
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Another fun fact, GM/AC doesn't make/package any type of oil/lubricant. It's all third party/privet label. And it's possible to have several different manufactures that meet GM spec., bottle the oil for GM. It's like the trans oil, made /bottled by Mobil in GM labeled bottles
 
I use Amsoil on all my cars and trucks. Great results for the past 30 years. Minimal wear on all wear parts.
That's nice. You're not doing your G80 locker any favors if that gear oil has friction modifier, though.

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