99 Silverado - Locking Diff ? & Fluid ?

Hello all, I have a 99 Silverado 1500 4x4. According the RPO codes I have the G80 Locking Rear diff with the 3.73 gears. The blue tag on the diff calls for 75w-90 Synthetic, so I bought the Mobil1 gear oil. I'm
wondering do I also need to add some sort of anti-slip additive?
Or is the G80 Locking differential different from limited slip differentials that require a special additive?
Thanks DP
BTW I intend to put the same in the front diff, but I've read here something about a front vent that needs to be changed because it's made of plastic. Is that true for the 99's and up? Seems bizarre to me that the syn gear oil could ruin a plastic vent tube, the stuff comes in a plastic bottle.
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Fairly sure the Mobil-1 includes the additive, but it's also not needed with the G80. Not sure about the vent, I've heard the same thing, and seen posts about it on web forums. There's a good one on the forum at www.gm-trucks.com in the 1500 forum, I think.
wrote:

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dpfishboy wrote:

You don't need any additive in the rear diff.

Yes, there is an updated white vent for use with synthetic fluid. If you don't change the vent, the synthetic fluid reacts with the original black vent and it will often loosen up and fall out of the diff.
Ian
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Ian,
I was going to stop by the Chevy dealer this week and see about this replacement vent tube that is mentioned in this thread. I put synthetic gear oil in mine as of this past summer and would like to replace the tube before it fails. Is there anything that I need to tell the parts guys to get this updated tube? Ask for the white colored tube? Or do they just come that way now?
Thanks Brian
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el Diablo wrote:

They will know which one to give you. It is white collared and the swivelling section of it is metal.
Ian
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Thanks Ian, I'll stop by and get one this week.
Brian
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dpfishboy wrote:

Yup,
The G80 is the "Eaton Mechanical Locker". It's engaged by a small flywheel that spins when axle speeds differ. It engages a ramp that locks to the two axles together. (rather violently, in my opinion).
-marc
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A great unit if not OVERLY abused. I had one (Was called a GUV LOCK then.) in my 1975 van that i put 220 000 miles hunting, pulling trailers over gravel mountain roads and using it often as a rescue vehicle for my stuck friends. Maybe they are weaker now, but i loved mine. old John

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ajeeperman wrote:

Yeah, I think they're definitely good for stock applications.
I'm into the high performance drag-race stuff, where they're not the best choice...
I've had three trucks over the years with them and this new one here _definitely_ works better than any of those older ones. I wonder if any changes were made? The truck is also all wheel drive, so that definitely helps some.
-marc
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Check out
http://www.tractech.com /
and
http://www.eatonposi.com /
The Eaton page has animation to show how the G80 works, They also offer a clutch unit. Tractech link owns Detroit locker, they also offer other designs.. some based on the old Spicer power-lock
JJ

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