GMC Rear Axle Codes

[Rafs]

Group,
RPO and Axle type codes came from crawlpedia. Anybody know why there is a code for "Positraction" and one for "Positraction Rear" ? My 1997 Yukon 4wd has the G80 or Positraction code. The other image is my codes: ... Thanks!

I also gave it the real test. On my shops slick concrete, I blocked the front wheels and eased into the gas. Two beautiful skid marks

 

[east302]

The G80 is the only one that GM offered in these, so the list may be pulling from other models. Believe it’s an Eaton M locker which GM calls the gov-lock.

 

[YukonGTmaster]

I don't see it on my RPO codes. I can only remember the right rear peeling out when I gunned it, unless I was in 4 HI.

 

[Marky Dissod]

The G80 is the only one that GM offered in these, so the list may be pulling from other models.
Believe it’s an Eaton M locker which GM calls the gov-lock.

Is this what some derisively refer to as 'Gov-Bomb'?
Read many stories in the 2000s about how this type of limited-slip tends to fail badly when it finally does.

 

[east302]

Yep, that’s the one. I’ve never had an issue, knock on wood.

 

[Marky Dissod]

Yep, that’s the one. I’ve never had an issue, knock on wood.

SO FAR, neither have I, knockonwood.
My concern is that, as it's a locker, it's an ON or OFF thing ... and that one day, it will just snap something ...

 

[Rafs]

Yep, that’s the one. I’ve never had an issue, knock on wood.

Is this, the G80, a locker or a limited slip/ positraction?

 

[east302]

I think it’s more of a hybrid between the two - an automatic locking differential?

 

[Marky Dissod]

My understanding - PLEASE, correct me if I'm wrong! - is it's NOT a limited slip differential, really.
According to the manual, the differential is simply open, UNLESS the rear wheel speed difference exceeds 100RpM.
Once the rear wheel speed difference exceeds 100RpM, it's locked.

1. Don't understand how or why it unlocks. just know that it does, eventually.
2. '100RpM' is almost certainly an oversimplification.
If one wheel spins 101RpM, and the other spins 001RpM, it should lockup.
If one wheel spins 2000RpM, and the other spins 2100RpM, does it lockup or not?

Would prefer a torque-sensing differential ...

 

[east302]

Here’s a video someone did showing the lockup with the spider gears. I suspect it’s all those little moving parts that cause the headache if they grenade.