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So I have a Gu6 for my rear diff, I was wondering what would be the best for offroading? I saw the g80 is locking? would that be the way to go? I couldn't find anything online, prob just my lack of computer skills so if someone could send me a link to the diff and maybe lockers for a gu6 diff if there are any out there it would be greatly appreciated.
 

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Standard axle on a GMT360 is the 8.5/8.6-inch ring gear unit, originally designed for compact and intermediate cars with small-block or six-popper engines.

I have heard of--but never seen--a 9.5" ring gear axle was used on a few GMT360/370 vehicles. IF (big IF) this actually exists, it'd be MUCH stronger than the weakling 8.5"/8.6" axle.

The G80 "locking" differential in the 8.5 axle has a bad reputation. They're a "Gov-Lock" differential, but acquired the name "Gov-Bomb".

The version of the G80 in the 9.5" axle has a much better reputation.

Either G80 versions needs "special" rear-axle lube; and "good luck" finding it. The original part number has been superceded so many times I can't tell what the official GM lube is supposed to be; and it's no better in the aftermarket. GM released a "service bulletin" that's so poorly worded it's impossible to tell if the G80 lube is supposed to have NO friction modifier in it; or if you're just supposed to not add ADDITIONAL friction modifier.

Or buy an aftermarket locking differential, and avoid the GM lube issue entirely. I bought an Eaton Truetrac for my K2500, but it's not installed yet.

"Off-Roading" generally involves bigger tires, and thus the need for higher-numerical gears. GU6 represents a gear ratio, not a differential style. You've got 3.42 gears now, and you probably want 4.10 or higher. Maybe you can get by with "4Lo".
 
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So I have a Gu6 for my rear diff, I was wondering what would be the best for offroading? I saw the g80 is locking? would that be the way to go? I couldn't find anything online, prob just my lack of computer skills so if someone could send me a link to the diff and maybe lockers for a gu6 diff if there are any out there it would be greatly appreciated.
The very BEST differential for what you need is the following:








Motor vehicle Automotive tire Font Auto part Automotive fuel system


M26-Pershing differential--- available now at most Army-Navy Surplus

With this much weight, G80 Posi-Traction isn't even necessary.
 

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Standard axle on a GMT360 is the 8.5/8.6-inch ring gear unit, originally designed for compact and intermediate cars with small-block or six-popper engines.

I have heard of--but never seen--a 9.5" ring gear axle was used on a few GMT360/370 vehicles. IF (big IF) this actually exists, it'd be MUCH stronger than the weakling 8.5"/8.6" axle.

The G80 "locking" differential in the 8.5 axle has a bad reputation. They're a "Gov-Lock" differential, but acquired the name "Gov-Bomb".

The version of the G80 in the 9.5" axle has a much better reputation.

Either G80 versions needs "special" rear-axle lube; and "good luck" finding it. The original part number has been superceded so many times I can't tell what the official GM lube is supposed to be; and it's no better in the aftermarket. GM released a "service bulletin" that's so poorly worded it's impossible to tell if the G80 lube is supposed to have NO friction modifier in it; or if you're just supposed to not add ADDITIONAL friction modifier.

Or buy an aftermarket locking differential, and avoid the GM lube issue entirely. I bought an Eaton Truetrac for my K2500, but it's not installed yet.

"Off-Roading" generally involves bigger tires, and thus the need for higher-numerical gears. GU6 represents a gear ratio, not a differential style. You've got 3.42 gears now, and you probably want 4.10 or higher. Maybe you can get by with "4Lo".
GM specifically noted that ANY multi-weight hypoid lube is OK if it doesn't have any sulfur in it.

Sulfur is used as a cushion to the gearset where it meshes under load to spread the shock out to a larger footprint on each tooth - that's all.

But it is not good for the sintered bronze material in the slipping clutches on/in any limited slip clutch pack.

If you want to, you can use a decent synthetic multiweight that starts around 70#W or 80#W, and ends anywhere around 120#-140#.

FWIW ----> if one practices a modicum of intellect when driving a Gov-Loc, then they are really very serviceable and long lasting.

I have over 200K miles on a bone-stock rear diff in my '86 K5 Blazer that is just as good as the day it was new.

DON'T ('do' any of the following to ANY limited slip differentials) ........
1> spin one tire on ice/snow/snot and have the other tire on asphalt or dry pavement​
2> fail to "preload" the differential before asking it to perform​
3> fail to service it at LEAST 3 times in the life of the vehicle or 300K miles, whichever comes first​
DO take it out for a literal spin once in a while, doing tight figure-8's in a dry parking lot to exercise the clutches and keep them lubricated.

Clutches, just from sitting and not being used, will push/squeeze the lube off the surfaces and temporarily "weld" them together.

IF you feel like there's an earthquake in the rear of your car as you drive from a stop or at slow speed --- start looking for a parking lot to exercise those clutches and the problem will go away.

I've had Detroit, Posi-Traction and Gov-Lok in many vehicles and they all work well ---- IF you know what it is with which you are working!


 

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GM specifically noted that ANY multi-weight hypoid lube is OK if it doesn't have any sulfur in it.

Sulfur is used as a cushion to the gearset where it meshes under load to spread the shock out to a larger footprint on each tooth - that's all.

But it is not good for the sintered bronze material in the slipping clutches on/in any limited slip clutch pack.

If you want to, you can use a decent synthetic multiweight that starts around 70#W or 80#W, and ends anywhere around 120#-140#.
The Service Bulletin I read was concerned about "Friction Modifier"; specifically how it made the lube "too slippery" for the carbon-based clutches in the Gov-Lock. Then the Gov-Lock doesn't engage because the clutches slip.

The problem is that they tell you to not "add" Friction Modifier, but they don't tell you whether or not the recommended lube already has some friction modifier in it already.

My 9.5" Gov-Lock is running on lube with no friction modifier at all, but I don't put enough miles on the thing to really know how that's gonna work long-term.

FWIW ----> if one practices a modicum of intellect when driving a Gov-Loc, then they are really very serviceable and long lasting.

I have over 200K miles on a bone-stock rear diff in my '86 K5 Blazer that is just as good as the day it was new.
Yeah, but you probably don't have an 8.5 axle in that thing. I'd expect a "12-bolt" 8 7/8 axle, which is a far better unit than the 8.5. The Gov-Loc problems are really with the 8.5" axle, and the smaller ones--7.5 or whatever it is.
 
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