I have a 1994 1500 Silverado Full Size Blazer 4X4 with stock GT4 gear ratio in a 10 bolt posi. Found a G80 from a 98 Z71 Truck 4X4. Is this a direct change out without modification or issue???? This is the entire rear axle/differential assembly with brakes and both are 6 lug. I got burned from a junkyard and I this is a decent deal on the G80. I just need a back up rear end once the one I have goes out. I don't do heavy off road, just need this vehicle to work.

 

GT4 is your gear ratio. G80 is the construction of the differential center section itself.

I believe that it should swap over, but you will want to verify that the leave spring perches are at the proper spacing and, even more important, that it has the same gear ratio as your current rear end.

So do you have a posi now? If so, why would you want to go to the G80?

 

swartikk,
Thanks for responding. I am a novice to this stuff.
The code in the glove box is GT4. I have been told that this means the gear ratio is 3.73. And that it has posi-traction.
The entire rear end was replaced in 2005 by a reputable mechanic shop but went out recently and ground the gears to razor blade thin.
I had this replaced with a 3.73 posi GT4 rear end from a junkyard and this used rear end is making noise at 55mph and worse at 65mph went foot is let off the gas pedal. ( Junkyard wont refund, mechanic is shade tree and disappeared)....OOOPs!

I have a deal working with a guy that has a G80, 3.73 ratio posi from a 98 Z71 4x4 truck.

I want to be absolutely positive this will work and fit before I purchase. The guy is going to let me ride with him in his truck to listen to the rear end he has. I will measure leaf spring perch separation and o.c. tomorrow when I am there.

If his G80 fits and gives me basically what I have now, then I want this for when my junkyard rear end goes out. Please let me know. I will also ask at the Chevy Dealership too.

 

The G80 is not necessarily a "posi" if I remember, as I do have it in mine, I think it is a locking diff.... So yea.... I believe there is a slight difference between locking diffs and positraction differentials...

 

What year and model do you Have?

I see GT4 and G80 in this order on the glove box parts list.
GT4 is in the third column from the right hand side of the list, second row from the top...G80 is just to the right of GT4.

How do you read these things anyway?????

swartikk said: "G80 is the construction of the differential center section itself"
What does that mean exactly? I am new here and not learned in the terminology. I understand pictures/images better. Thanks.

 

Well in the glove box there are a list of RPO codes....

G80 is the designation of the factory "locker"

GT4 is the ratio.....

You can have both RPO codes as they are semi independent.
I have a 1998 4dr 4x4 Blazer and have the G80 code as well as the GU6/GU4 code... I think its one of those as I have a 3.42 gear ratio....

 

Semi-independent ! That sounds like the phrase "a little pregnant", if you get my drift here ! lol.!!!

Still not convinced on what to do here.
Note: His G80 was rebuilt from a 3.42 gear ratio (RPO) to a 3.73 gear ratio. So the gear ratio now matches mine, no problem. He is upgrading to a 14 bolt and now no longer needs his rebuilt G80/3.73 differential assembly. He noted that his G80 has larger brakes as well.

I suspect that the only way I will know is more research and questions to the dealer parts guys. Certainly will take all measurements I can today.

Does GU4/GU6 mean Gov-LocK? I have heard that Gov-lock is not re-buildable.
I don't want Gov-Lock as it seems to be a complete tosser once its gears are fried.

 

Gov-lock is what the G80 is. There are a few different names for it and it is re-build able but not worth the cost. Ok for the rear end you have now. How do you know it has posi/limited slip/gov-lock. Just because it has 3.73 does not mean it has posi. GT4 is the code for just the gear ratio. G80 is the code for posi/limited slip or whatever you want to call it.
For the new axle you said it has a G80. Ok but what is the gear ratio? It will have to be GT4(3.73) for it to work. When looking for a new rear end I would just look for the ratio. Dont worry about the G80. They will cost more and they really dont work that good if it works at all.