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Possi or limited slip?

M

Marshall

1/2 ton status
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I have a 1987 GMC JImmy(k-10) 10 bolt, and i know that when i looked to see which direction the wheels went, they went opposite direction of eack other when i was moving them with my hand, i am wondering if this is possi or limited slip.Thanks for any help.
/forums/images/graemlins/k5.gifMarshall /forums/images/graemlins/1zhelp.gif
 
posi and limeted slip are different names for the same thing. A clutch type locking differential. BUT if you jacked it up and tires went opposite directions, you most likely have an open diff or very worn clutch's.
 
OR, in our case, it might be a gov-lock. The SPID sticker in the glove box (if still present) will tell you. If you have code "G80" on that sticker, unless someone has removed it, you have a Gov-Lock.

You can try spinning one wheel really fast, but its kind of hard the larger the tire. Gov-locks, if working properly, will lock if you can spin one wheel fast enough by hand. Make sure both are off the ground.
 
Probably open. Look at the RPO sticker. If there is one that says G80 it's either clutch-type limited slip or a Gov-Lock.
 
Don't think G80 meant anything BUT Gov-Lock after the early 70's in trucks. I know for a fact '85/'86 you either got an open diff or gov-lock in half tons, and thats it.
 
I think 99% of the time it does mean Gov-Lock. However, my aunt and uncle's 89 half ton says G80 on the sticker and it's got a nearly worn-out limited slip in it. I've also seen a 91 with the same thing. Maybe they were mess-ups? I don't know. I know in both cases the rear ends had never been apart.
 
If it is not a Go-vlok in your aunt/uncles ride, I believe that dealers would replace blown out Gov-loks with Auburn LSD's(limited slip diff's).....
 
I highly doubt GM would but a disposable limited-slip in any vehicle they worked on. I don't even think GM is that stupid. Auburn limited-slip differentials are cone type and are pretty much worthless. They're good for ~40,000 miles and nonrebuildable.

And besides, I'm pretty sure I mentioned that neither of the axles had ever been apart.

There's no mistaking a pair of clutchpacks with a Gov-Lock.
 
Well there was a person on here in the past that had their Gov-Lok go and had the dealer repair it. I do remember they said the dealer installed an Auburn LSd as a replacement!

I have never heard of any other LSD's used in Gm vehicles(10 bolts) other than the Gov-Lok.
 
Checking my '82 service manual, these are the "limited slip differentials" listed:

Eaton limited slip ("traditional" setup, clutch packs, 4 springs)

Chevrolet limited slip (also "traditional" except "S" shaped spring instead of 4 individual coils as above)

Borg Warner (cone type, same as Auburn, non-rebuildable)

Power-Lok (another style clutch plate setup)

And finally, the much loved Eaton Positive locking Differential, also known as the Gov-Lock.

This covers all 5 or 6 types of axles that may have been installed in '82, so the first three limited slips are *probably* all 1/2 ton units, (simply because I've never seen these used in anything "heavier") with the gov-lock crossing over with the 3/4 tons. (1 tons too?)

Power-Lok, that was a one ton piece, correct?
 
I checked the RPO sticker and it says G80 along with a bunch of other numbers. So does my rear-end have a locker in it? where can i find out what all those other RPO codes mean.If you can help i would appricate it very much.
Thanks,Marshall/forums/images/graemlins/k5.gif
 
My auburn I got from macromotive. It was messed up the first time alot of clicking and grinding. Tore it down drove it up to the factory here in IN they fixed it on the spot and gave it back to me same day. Has worked perfect ever since! I use to EAT the GM limited slip's in mud and snow (doing dounuts). This new auburn added new life to the truck! J
 
In my opinion, you'll need to pull the differential cover to see. If there were other options besides the gov-lock, you really can't know what you have, since whatever is in there could be malfunctioning, acting like an open differential anyways.

It's never a bad idea to change 12 year old differential fluid : ) I'd bet RPO codes have been discussed here before (use the search feature) and also www.gnttype.org has a pretty comprehensive list under the tech sections, as do a few other places. Of course RPO's and the actual item (such as G80) could mean different things on a car and a truck, in '85 or '86 in a half ton, G80 would have been the gov-lock for certain, while G80 in a car same year would have been limited slip. (eaton or chev style more than likely)
 
I checked the oil and it was pretty Dirty. Everything thing inside looked good. It looks like a Gov-Lock locker. My other question is which oil to use 80-90w is recomended for my 10 bolt but it also says to add an additive to it for the locker. Any help would be appriciated

/forums/images/graemlins/usaflag.gifThanks,Marshall /forums/images/graemlins/k5.gif
 
I really don't know /forums/images/graemlins/smile.gif

GM service manual said no limited slip lube necessary, yet it uses clutches like limited slip diffs, so who knows?

I don't think you'll harm anything throwing in some limited slip additive. I did, and have been driving that way for a few years now.
 
I very much doubt all of these differentials were available on a particuliar model. Most likely this list includes every different type of diff offered on any GM product that year, so for example these included diffs in cars, heavy trucks, etc.... In other words I doubt GM offered three or more different limited slip diffs in a 10-bolt axle on a truck.
 
Ok, why then would GM offer the 8.5" (10 bolt) in cars in '86 with the Chev style posi, yet have the trucks receive the gov-lock? 7.5" S-10 diffs and car diffs were the same...S-10's got gov-locks (at least most of the time) while the cars got either the Auburn, Eaton, or Chev style posi.

You are right, it doesn't make any sense as to why GM did what, but thats fairly typical.

Since the '82 C/K service manual lists all of them, it's not out of the *realm of possibility*, that they did, in fact, use each and every one, at least in some cases, especially since the Eaton, Chev, Auburn, and Gov-Lock were ALL offered in 10 bolts.

Of course, the service manuals HAVE been wrong before. With others saying the diff's are stock, from new, and having limited slip diffs, instead of the gov-lock, I'm inclined to think GM may have let some out the door when they were short on gov-locks, or whatever. It would have made sense (cost wise) for ALL 10 bolts car or truck to get the same type of diff, but we know that wasn't the case.
 
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