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Discussion Starter · #1 ·
Hey y'all,

Undid my rear diff cover today to swap it out because the previous owner had dented the cover.

I have a 3.73 ratio with the G80 - and my closest auto shop only sells 70W-90 gear oil with the "Limited Slip" label. I know I don't have limited slip, but will this limited slip hurt my G80?

Also, I included some pictures from under the cover, the gears had some chips, burrs and flakes here and there. Was wondering if any of you could take a look at them to see if there's any signs of my G80 turning in to a bomb any time soon?

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GL5 80-90 wt gear oil without limited slip additive. Is what GM requires for the Gov Lock G80 equipped Diff in older trucks. I do not like to use synthetic oil in G80..
Friction modifiers will allow a small amount of slip in the clutches. This stops clutch chatter in turns with LS diffs. The G80 Gov lock is not a limited slip. It is a automatic Locking differential. You do not want any clutch slip or you will wear out the clutches. Possibly causing a catastrophic fail.
From the pics. The teeth on the ring gear look pretty good to me . The wear pattern is in the middle of the tooth where it should be. Gov locks in 14 bolt rear ends are fairly strong units and hold up well as long as they are maintained with regular oil changes with proper fluid.
 
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Based on the photos you for sure do not have the stock gov lock guts in there. Yours has been replaced at some point. I don't know the aftermarket ones by sight. Hopefully someone will recognize it and then you can figure out what oil its supposed to use. Some can be very picky.

I can't see much in the tooth photos but where you have circled isn't were the gears touch so I suspect its just leftover from the machining process and like so many things these days they just didn't take the time to clean that up since it should not effect performance. Those dots are strange, seems like some sort of identification someone put on? Maybe the guy that installed it?
 
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That is a G80 gov-lock. The 14 bolt version looks different than the smaller units.
Here is some good info on ID'ing the different carriers.
 
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Discussion Starter · #5 ·
Those markings on the left side is weird indeed...

I decided to roll the dice and go with a Norwegian brand SAE 80W-90 LS - if the gears aren't happy with it, I'll swap in something else. Read on Bob Is The Oil Guy that LS won't do any damage to a G80, hope that turns out to be true!

Thanks for the input from all y'all. 6.5's all over the world are lucky to have ya.
 

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Discussion Starter · #6 ·
Oh, and I put in a magnet on the cover and one on the bottom as visible on the bottom in the photos - is it possible that the magnet will interfere with the gears in this position?
 

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Use LS oil at your own risk. It is not the gears you have to worry about. The clutches in the Gov lock unit that are the issue. You do not want them to slip. The clutches and activation mechanism are internal and not visible There is no way to tell if damage is being done until it explodes.. Having clutches slip, then suddenly engage is what destroys Gov locks.
I have been running and building hard core 4x4s all my life. I am talking from experience in building bullet proof drivetrains capable of rock crawling, deep mud and snow, and running large tires.
You can get away with gear oil with LS additive in it. If you just drive on the street or mild 4 wheeling. But getting off road, and in Mud, Ice and snow makes the Gov lock work all the time Locking in and out. That is where the clutch slippage causes big problems. I dont care what someone on the net says about" LS can be used in a Gov lock". It is not good for it.
Yes that is a stock Gov lock.
All you really need is the magnet on the bottom of the case.
 
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Discussion Starter · #8 ·
Valuable and experienced input Tommygunner - I don't do any offroading. There's absolutely a lack of good oil in Norway, and will probably drain the rear diff in the near future when I find a better alternative.

I thought LS would literally limit the slipping (less slipping) because of the name, and saw that it was a SAE 80W-90 GL-5.
 

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@Tommygunner I recently changed my rear diff lube... also have the 14-bolt with the G80 (4.10 gears). I used Lucas synthetic 75w-90. The bottle says it works with limited slip diffs, but doesn't say that it is specifically designed for that. It's marketed as all-purpose. Not sure if I made a mistake or not?
 

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IMO. Synthetic oil and Gov lock do not mix. As i said before An Eaton MLocker... AKA, Gov Loc, GM spec G80, is Not a limited slip! It an Automatic Locker. They work best with conventional GL5 80-90 lube.
Gm does recommend synthetic 75-90 for their newer truck differentials. But I have seen people who use their trucks hard, have problems with the clutches chattering/slipping and jerky engagement., You dont want that. The fix is to change fluid and use conventional GL5 80-90.
The fluid GM recommends for your 96 truck G80 is conventional.80-90. My truck is a 98. The owners manual says to use conventional GL5 80-90.
I am not familiar with the lucas oil. But Problem with many of the newer synthetic fluids is, they contain friction modifiers.
If the Lucas does not have friction modifiers added for limited slip diffs it should be good.
If you do run the Lucas and experience chatter or jerky engagement of the locker. Change back to conventional GL5.
Here is info and a little vid on the Eaton M Locker, how it works and it built. The locker pictured in the page is a GM 10 bolt locker. They look a lot different than the one in your trucks 14 bolt because all the workings are covered up with metal and internal. But work exactly the same way. The 14 bolt locker is a lot stronger than the 10 bolt locker. 10 bolt Gov locks are also known as "Gov- Bombs".
 

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Anyone got an exploded diagram of this HD gov lock? I'm having trouble figuring out how they shoved all those little gears and weights into that housing and still had room for decent sized gears. Or did they come up with something less flimsy looking for these? The smaller ones you can sure see why they said the G was for grenade because there was a lot of small parts whipping around in there.
 
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