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OK, whatever. Ive used it in about 300 vehicles with Posi rear ends and locking rear ends; all work just fine, zero issues. Some of them actually had water in the rear end lube when it was drained... yucky stuff. Part of it is that I do use the 75W/140 in some cases as well. Specifically if the truck is being used for towing, or is always carrying a heavy load.
Lester I'm not trying to be difficult but Drax is 100% correct on this subject.

I personally can tell you, if you put in a lube with friction modifiers in it, as I mistakenly did, the G80 will not function properly. Watch some G80 videos on youtube, look at the design of the locker. You will see the first action after the delta of the 120 RPM differential is met the engagement pawl will start the locking process. Once mechanically locked rotational power is delivered to the clutch pack. If modifiers are present it will cause the clutch pack to slip way more then system design was engineered to allow (IE it won't lock the axles together, they will slip and be at different RPMs).

The purpose of the clutch pack is a smooth the transition of power based on applied pressures with a known coefficient of drag in the inherent design. If you add an additive/friction modifier, the clutch mating surfaces will slip due to being out of pressure specification, this is based on the coefficient of drag expecting no additive/friction modifiers . Simply, not enough designed pressure to overcome the slippery additive/friction modifier.

Sure if you never meet the 120RPM requirement of slip between axles it won't matter if you've put the wrong fluid in, but, if a need arises I can assure you from personal experience it will not function correctly if friction modifiers are present.
 

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I just changed my diff oil at 75,000 miles. I used Mobil Delvac. I will say, judging by appearance only, the rear certainly needed the change. The front didn’t look too bad. There was next to no metal on both drain plugs. When you change it, don’t mix up the fill and drain plugs as only the drain plug has a magnet.
 

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I just changed my diff oil at 75,000 miles. I used Mobil Delvac. I will say, judging by appearance only, the rear certainly needed the change. The front didn’t look too bad. There was next to no metal on both drain plugs. When you change it, don’t mix up the fill and drain plugs as only the drain plug has a magnet.
Thx terryjm. I'm showing operational ignorance here, but I excused myself for not changing out my front diff when I did my rear (~43K miles) because it probably had/has 20 rolling miles on it. Is their wear on it that I'm missing, or some other reason for me to change it out? FYI, I am now at ~65K miles.
 

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Thx terryjm. I'm showing operational ignorance here, but I excused myself for not changing out my front diff when I did my rear (~43K miles) because it probably had/has 20 rolling miles on it. Is their wear on it that I'm missing, or some other reason for me to change it out? FYI, I am now at ~65K miles.
I purchased a gallon of the oil. I really do not think the front needed to be changed but since I had the oil and pump out anyway, I just did. I use a small cheap 12 volt pump and it is messy. It was worth the $20 I spent on the oil to not have to clean it again someday when the front needed to be changed. Also, while I really doubt any moisture got in, I have read it’s a good idea to change it if for no other reason to assure any moisture inside is removed. I also usually fall victim to the “since I was in there anyway” mentality.

As a side note I originally purchased high dollar oil for the diffs but then realized it had friction modifiers. I used that in my old Land Rovers. It was a diff oil changing day at my shop. LOL, the “mass“ diff oil change was largely driven by my desire to not clean up the pump and ancillaries more than once. I also changed the oil in the Land Rover transfer cases, as I was trying to use all the oil with friction modifiers. The old land rovers are not overly particular about the oil you use. On another side note, I use Redline MTL in the Land Rover gearboxes. It is the only time I have changed oil in anything where I noticed a significant improvement after changing from a different type of oil.
 

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I purchased a gallon of the oil. I really do not think the front needed to be changed but since I had the oil and pump out anyway, I just did. I use a small cheap 12 volt pump and it is messy. It was worth the $20 I spent on the oil to not have to clean it again someday when the front needed to be changed. Also, while I really doubt any moisture got in, I have read it’s a good idea to change it if for no other reason to assure any moisture inside is removed. I also usually fall victim to the “since I was in there anyway” mentality.

As a side note I originally purchased high dollar oil for the diffs but then realized it had friction modifiers. I used that in my old Land Rovers. It was a diff oil changing day at my shop. LOL, the “mass“ diff oil change was largely driven by my desire to not clean up the pump and ancillaries more than once. I also changed the oil in the Land Rover transfer cases, as I was trying to use all the oil with friction modifiers. The old land rovers are not overly particular about the oil you use. On another side note, I use Redline MTL in the Land Rover gearboxes. It is the only time I have changed oil in anything where I noticed a significant improvement after changing from a different type of oil.
Thx terry. What did your old front end oil look like? I checked back on my maintenance notes and here's what I said about my ~43K mile rear oil:
change rear diff fluid. Mobil 1 75-90. Old was black, and some wear particles in magnetic plug.
 

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At 75,000, my rear diff oil matched the description of yours at 43,000. While both plugs had very little metal on them, the rear was probably twice the front. The front oil was not nearly as dark as the rear. The rear was just a shade under black. The front was slightly “grayed.” Also, the metal on both plugs was very fine. I couldn’t even feel anything gritty in it.
 
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