Fluid for G80 rear end in 02 silverado?

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EasTn
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Can't find a definite answer. Rear end code says my truck has a G80 limited slip 342 gear differential. But have read not to use fluid with LS additive, other places say yes use LS additive. Even read a notice from chevy saying not to but have heard that a new notice has been put out since then. It calls for synthetic 75w90 but since idk what the heck to put in it I opened her up sprayed her out with parts cleaner and refilled with 80w90 conventional valvoline. Two quarts without LS additive and almost a whole nother quart with LS additive. Since I cleaned it out I will just drain and refill if I have find out what in the world is supposed to be used in it. Anyone know for sure?
 
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You "can" run a LS fortified fluid, But technically it doesn't call for it. Mobil Delvac 1 75w90 or Redline 75w90NS are the fluids I would run in a Gov-Loc. The LS gear oils don't usually have enough LS additive in them for aftermarket high performance clutch type posi's.....I don't think "most of a quart" will matter.......
 
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I think it is a locker, not a clutch type limited slip. So, it does not need the LS additive, but being in the fluid will not affect it. You should be fine. I think the GM fluid calls for synthetic however as you state. I prefer Amsoil 75W-110. If you're not towing, not having synthetic probably won't hurt. If you tow, better put the synthetic in.
 
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Originally Posted By: WishIhadatruck
I think it is a locker, not a clutch type limited slip. So, it does not need the LS additive, but being in the fluid will not affect it. You should be fine. I think the GM fluid calls for synthetic however as you state. I prefer Amsoil 75W-110. If you're not towing, not having synthetic probably won't hurt. If you tow, better put the synthetic in.
While it is a technically a Locker.....It does have Clutches, They are just never engaged during a turn & don't need the Anti-Chatter LS additive.
 
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Thanks gentlemen. I don't think it is locking the way it should as it sometimes is a one wheel wonder even in a strait line.
 
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I have had and still have trucks w the g80 rear diff and they do not require LS fluid. You can use any 75w90 or 80w90 in it. I have used both types and it ran normal zero problems
 

4WD

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Originally Posted By: clinebarger
You "can" run a LS fortified fluid, But technically it doesn't call for it. Mobil Delvac 1 75w90 or Redline 75w90NS are the fluids I would run in a Gov-Loc. The LS gear oils don't usually have enough LS additive in them for aftermarket high performance clutch type posi's.....I don't think "most of a quart" will matter.......
Using Mobil Delvac 1 in my G80 for two years now … smooth as silk and pulls on both wheels in sand/dirt/mud
 
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I've been using mobil 1 75w90 ls syn front and rear in mine for 10 years. G 80 rear. Mine drives all four tire till one spins in front, then I just have three and it turns hard!
 
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Originally Posted By: Sealbilly
Thanks gentlemen. I don't think it is locking the way it should as it sometimes is a one wheel wonder even in a strait line.
How do you know it still has it's Gov-Loc? It wouldn't be the first 8.5"/8.6" differential to have catastrophic failure of the Eaton Governor Locker & a open differential installed.
 
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I run AMSOIL's Severe Gear 75w-90 in my 02's diffs, I tow and have 177k on the vehicle. Sent a sample off that the fluid had 90,516 miles on it.
 
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If its a gov lock locker you do not need a limited slip fluid. There are no clutches in that type of locker.
 
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I have a 2012 Silverado and am using straight non-synthetic 80W-90 in it and I tow heavy stuff too. Works well from what I can tell. FWIW mine doesn't have any warnings on it.
 
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Originally Posted By: joegreen
If its a gov lock locker you do not need a limited slip fluid. There are no clutches in that type of locker.
They do use clutches, But you are correct on them not needing LS additive.
 
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Originally Posted By: DoubleWasp
G80 diffs must have changed at some point. All of mine have metal warning tags on them that additive must be used.
My understanding is that G80 is an option code. Depending on the axle or vehicle, that could mean the mechanism is either a limited-slip or a gov-lock. One of my earliest posts was about the arcane GM spec number for axle fluid in my 2001 Silverado. It had the grape-scented special sauce from the factory. I ended up replacing it with Amsoil Severe Gear 75W-90, and the locker has continued to work for the last 70,000 miles.
 
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Originally Posted By: Rhymingmechanic
Originally Posted By: DoubleWasp
G80 diffs must have changed at some point. All of mine have metal warning tags on them that additive must be used.
My understanding is that G80 is an option code. Depending on the axle or vehicle, that could mean the mechanism is either a limited-slip or a gov-lock. One of my earliest posts was about the arcane GM spec number for axle fluid in my 2001 Silverado. It had the grape-scented special sauce from the factory. I ended up replacing it with Amsoil Severe Gear 75W-90, and the locker has continued to work for the last 70,000 miles.
Correct, both my Suburban and Roadmaster both have G80 option codes. They are completely different axles and differentials. The Roadmaster needs LS additive, the Suburban does not.
 

dnewton3

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I had looked into this topic DEEPLY many years ago when I had my Dmax/Alli with AAM 11.5" axle. Always go directly to the source! https://www.eaton.com/us/en-us/catalog/differentials/mlocker.html The G80 most certainly has clutches ... " Utilizing a flyweight mechanism and self-energizing clutch system ..." Here's the unit in a video; great explanation https://www.youtube.com/watch?v=ftyJvIO0DZ8 Note they call they clutches "active friction disc" and such ... The G80 requires a fluid with friction modifier, pure and simple. It is a clutch-driven limited slip unit. The reason they call it a "locker" is because it uses a fancy flyweight system to "lock" the clutches (essentially by just clamping down tighter on the clutch pack) to increase torque bias. The unit is ALWAYS in a LS mode; it only "locks" when a preset amount of wheelspin causes the clutches to lock up in a tighter grip. Hence, it's a fancy version of a LSD. And it needs some FM to work correctly. There is an old document from GM that states to NOT add FM to the fluid. This is a misleading statement. They (GM) sell their own diff fluid (affectionately known as "grape juice" because it has an odd odor of grape juice) and the over-the-counter product already has the FM in it. And because it is just as bad to have too much FM as it is to have too little FM, GM's position is "don't mess with our fluid; don't add FM". But it's really a matter of viewpoint. They are telling you not to add FM because they already add FM to the bottled product. What they should be saying is "Don't add any more FM; we already did it for you." The GM part number for their lube is 9986115. If you search old documents about it, you can read more. Amsoil even came out with a document a long time ago explaining the whole FM topic regarding GMs product, but I cannot find a copy of it at the moment. If you use diff fluid in the G80 that has no FM whatsoever, you will get clutch chatter and nuisance locking. Adding about 4 oz of FM to the fluid will be a decent place to start. Then add a tiny bit at a time until those nuance and chatter events go away. More than a decade ago I had a email conversation with an engineer at Eaton about this differential. I would told that all it needed was a GL-5 lube in a typical grade (dino or syn, 75w-90 up to 140 grade). Add in some FM if the fluid does not include it. Done.
 
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