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Hey! New to the forum. I inherited a 2003 Envoy from my grandpa when he passed this last summer. I’m fairly confident he swapped out the factory rear end with something else. Is there an easy way for me to identify if it has an LSD or the Eaton locker without referencing the RPO codes in the glovebox? Thanks!
 

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Hey! New to the forum. I inherited a 2003 Envoy from my grandpa when he passed this last summer. I’m fairly confident he swapped out the factory rear end with something else. Is there an easy way for me to identify if it has an LSD or the Eaton locker without referencing the RPO codes in the glovebox? Thanks!
I'm sure whatever he put in the vehicle won't be referenced by the RPO code any longer, especially when you state: "he swapped out the factory rear end with something else".

Testing it could create a problem if he used a Gov-Lock type, although I'm pretty sure with the <false> ideal that it is bad design, not many would consider going TO it.

Did he want to simplify and go with an open differential? Who knows!

You can confirm if it is a limited slip type, but no guarantee what system he bought. If you decide to "test" it by doing burnouts with one wheel in the dirt and the other on asphalt ... you can damage any of the limited slip driveline by trying that process to diagnose what you've got.

Pull the cover to confirm it ... are our TBs "C-type"?
I dunnow yet ... haven't had to open mine up so far ... I think they are though.​
Jacking the rear wheels off the ground and manually trying to spin one wheel or the other ... won't work, not conclusively.

You SHOULD find out, for sure, 'cause you need to use whatever secret sauce it needs when you service it every once in a while.

.
 

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Discussion Starter · #4 ·
I'm sure whatever he put in the vehicle won't be referenced by the RPO code any longer, especially when you state: "he swapped out the factory rear end with something else".

Testing it could create a problem if he used a Gov-Lock type, although I'm pretty sure with the <false> ideal that it is bad design, not many would consider going TO it.

Did he want to simplify and go with an open differential? Who knows!

You can confirm if it is a limited slip type, but no guarantee what system he bought. If you decide to "test" it by doing burnouts with one wheel in the dirt and the other on asphalt ... you can damage any of the limited slip driveline by trying that process to diagnose what you've got.

Pull the cover to confirm it ... are our TBs "C-type"?
I dunnow yet ... haven't had to open mine up so far ... I think they are though.​
Jacking the rear wheels off the ground and manually trying to spin one wheel or the other ... won't work, not conclusively.

You SHOULD find out, for sure, 'cause you need to use whatever secret sauce it needs when you service it every once in a while.

.
I seem to remember him buying a complete new axle for the vehicle. The other thing I don’t know is if he upgraded from the 8” rear end that I believe was the only option for the 4.2 I6. Given that the only locker available for the 8” was the factory variant, he may have wanted to go to the 8.5 or whatever it is that came on the models with the V8 since there are aftermarket lockers that fit that. I’ll have to do the test for the LSD and see what that yields me. Driving in the snow at slow speeds, like in a parking lot, I think I can feel a distinct clunk in the rear end after the tires spin for a second and then I have more traction. Could be the locker engaging?
 

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I seem to remember him buying a complete new axle for the vehicle. The other thing I don’t know is if he upgraded from the 8” rear end that I believe was the only option for the 4.2 I6. Given that the only locker available for the 8” was the factory variant, he may have wanted to go to the 8.5 or whatever it is that came on the models with the V8 since there are aftermarket lockers that fit that.
The stock axle was an 8.5 or 8.6; the Trailblazer SS and perhaps others got a 9.5.

All of these have aftermarket replacement differential cases with various forms of "posi" or lockers.

I’ll have to do the test for the LSD and see what that yields me. Driving in the snow at slow speeds, like in a parking lot, I think I can feel a distinct clunk in the rear end after the tires spin for a second and then I have more traction. Could be the locker engaging?
Yes, it could.

The 8.5.8.6 factory locker (Gov-Lock) is often called "Gov-Bomb". The units used in the 8.6 and smaller differentials do not have a good reputation. The 9.5 and 10.5 versions seem to be fairly robust.
 

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The stock axle was an 8.5 or 8.6; the Trailblazer SS and perhaps others got a 9.5.

All of these have aftermarket replacement differential cases with various forms of "posi" or lockers.


Yes, it could.

The 8.5.8.6 factory locker (Gov-Lock) is often called "Gov-Bomb". The units used in the 8.6 and smaller differentials do not have a good reputation. The 9.5 and 10.5 versions seem to be fairly robust.
Don't be so quick to call a Gov-Lock out ... I have one as the original unit in an '86 K5 with a stroker 350/383, a Crane cam and some early FI heads (small cc's) in front of a very highly modified THM700R4 (manual valve body) and 265/75R17s that I have never treated kindly and yet it works as it should every time.

That's over 30 years of my abuse on it and it hasn't failed yet hauling logs and 3-cord trailers (over 8k lbs) full of firewood in the snow - over stumps and into "oops" holes and trenches and swales and on the highway all summer and winter long.
 

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