Posi/LSD or open diff.

[Matthew Kesler]

Took my truck to a trusted mechanic to have some work done for a freshly bought truck. We bought it from a friend, 95 Chevrolet k1500 5.7 automatic. Got it back and was told the rear end was a “locker”. So we decided to test that theory out, and got confused. We went to an old backroad to give it some crap. So we did a burnout and sitting still it roasts one tire, but then you let go of the brake and let it move, and the other tire starts to roast with it but not NEARLY as bad, and just for a second. So I’m confused, do we have a locking rear and but it’s needing rebuilt or do I have an open diff?

 

[PlayingWithTBI]

Take a look at your RPO sticker in the glove box and see if you have a "G80" code. That's for the Eaton "gov Bomb" locker, ha ha.

https://news.pickuptrucks.com/2015/04/eaton-g80-locking-differential-keeps-gm-pickups-moving.html

 

[SUBURBAN5]

Best thing Is to check the I'd parts in the glove compartment. Otherwise you can raise the back wheels and spin it to see if they rotate the same direction

 

[Nickpisp]

Neither, Limited slip.

 

[Matthew Kesler]

Take a look at your RPO sticker in the glove box and see if you have a "G80" code. That's for the Eaton "gov Bomb" locker, ha ha.

https://news.pickuptrucks.com/2015/04/eaton-g80-locking-differential-keeps-gm-pickups-moving.html

I looked in the glove box and I seen the sticker with a bunch of letters and numbers (assuming that's the RPO sticker with tons of codes you're referencing) and amidst those codes I did see a "G80", what does this mean?

 

[PlayingWithTBI]

That means you have the G80 rear end. You can Google it and do some research. I saw somewhere they sell a rebuild kit with clutches for them. In essence when one tire spins ~100 RPM faster than the other the clutches will engage up to somewhere around 20MPH (IIRC), then it'll release. It's pretty much just for getting traction in the mud or snow, not for doing burnouts. That's when it will "grenade" and blow up the carrier if it gets too much torque.

 

[Matthew Kesler]

That means you have the G80 rear end. You can Google it and do some research. I saw somewhere they sell a rebuild kit with clutches for them. In essence when one tire spins ~100 RPM faster than the other the clutches will engage up to somewhere around 20MPH (IIRC), then it'll release. It's pretty much just for getting traction in the mud or snow, not for doing burnouts. That's when it will "grenade" and blow up the carrier if it gets too much torque.

Well I would expect it to lock up and spin both tires when doing a burnout right? Because the one tire is spinning much much faster than the other because the other is not spinning at all, and when I let go of the brake, the other tire spins just enough to give a little smoke but that's it.

EDIT: Also we tested a super slow tire spin on our dirt road. And when you brake torque it on the dirt road they both spin, but when the speed goes up, the left tire slows down to a stop and the right one keeps spinning. If I have the G80 then it must be broken or needing a rebuild right?

 

[df2x4]

Well I would expect it to lock up and spin both tires when doing a burnout right?

That's the thing about G80 lockers, they rarely do what you expect them to. They're pretty terrible honestly.

If you haven't already I'd drain the oil out of the diff and replace it with GL5 rated 80W-90 with NO friction modifiers or limited slip additive. Any type of additive in the oil will make a G80 even more unpredictable than they are by design, and most diff oil these days has some already in the bottles.

 

[b454rat]

Can't go full throttle with these doing a burn out. Need to get 1 tire barely spinning, keep it like that till the other one kicks in, if it will at all. Too much juice it will just spin and not lock in.

 

[Matthew Kesler]

That's the thing about G80 lockers, they rarely do what you expect them to. They're pretty terrible honestly.

If you haven't already I'd drain the oil out of the diff and replace it with GL5 rated 80W-90 with NO friction modifiers or limited slip additive. Any type of additive in the oil will make a G80 even more unpredictable than they are by design, and most diff oil these days has some already in the bottles.

Can't go full throttle with these doing a burn out. Need to get 1 tire barely spinning, keep it like that till the other one kicks in, if it will at all. Too much juice it will just spin and not lock in.

I gotcha, our mechanic had already replaced both diff's fluid. Not sure what he put in there or what additives etc. But I will definitely keep this in mind. Also are you sure about no friction modifier or limited slip additive? What about the front end fluid?