I'm looking at my RPO tag for my 98 blazer and it says GT4 G80 and i'm thinking it is a slip/posi with 373 gears... I am replacing the front 4x4 unit with one that has a GU6 RPO code. 343 gears... Naturally I have to change out the gears to match but what i'm wondering is, can i take the rear end gears ( 343) and use my Posi carrier? or am I just going to have to give up the posi?

Never did a ring and pinion job on a rear end yet and people give me that look like OMG I'd just replace the whole rear end instead of the gears. so let me ask ya, the hard part is just setting clearances with shims to get the gears to mesh properly? where do you buy shims for it? any auto parts? I wish there was a utube video on how to..

 

I'm trying to follow your question. You vehicle has 3.73 front and rear and G80 locker in rear.

You are replacing the front with a 3.43 one and you know you have to change the gears....

1) is the old front diff trashed? Mine was.
2) do you actually have another pair, both front and rear diffs which are 3.43, and that rear diff is NOT G80?
3) do you wish to end with 3.43 or 3.73 in your vehicle?

Setting up a front diff is much easier for two reasons, there are no shims to change, only adjusting nuts, AND since it's used only occasionally, a little whine is not a big deal. Setting up the rear diff is a bit more difficult.

My guess is your 3.73 front gears are shelled and you are hoping to go 3.43 front and rear. My other guess is that you are asking about using your G80 in the 3.43 rear end.

I'd discourage this. Go buy a 3.73 front diff. Ebay has them for $300. Don't mess with your rear end.

 

what happened is.. when i bought my blazer in the summer last year.. the previous owner replaced the front end with one from a salvage yard. I never checked the 4X4 out when i bought it, but in december I tried it out and under accel I hear this aweful noise like a bad drill motor.. it would go away when i let off the gas. so I got under the front end and first thing i saw was the 2 wire plug disconnected and found out there was a old plug in the socket broken off. 2nd thing i noticed is the drivers side Axle was not in all the way. and I could not get it to snap back in.. pulled the ball joint and pulled the axle out to find the splines were damaged like someone hammered them . so using a v file i cleaned out the splines and then found the splines in the transfer case itself were also mushroomed. well needless to say after many hours of cleaning them out I got the axle back in and snapped in. I refilled the axle and found it to be almost 1 qt low. but it still is making terrible noise. I fear the gears are prolly ground up from being low on oil. however in 2wd the front end makes no noise at all. Soooooooooooo

I bought a 98 Blazer that had a shot body but good quiet and fully working 4X4. I pulled the front off, pulled the whole rear end off and scrapped the rest. bought the whole Blazer for $140 so I was thinking much cheaper then just buying a ring gear. After checking my RPO tags seeing mine was a 373 with a limited slip posi, I looked at the Donor car RPO tags and it said it was a 343 but no posi. some of the locals said just take the ring gear off and put it on the Posi carrier.. changing the ring and pinion of course. I have never however had a rear end out other than to replace axle seals. I would not know a posi carrier if it was right in front of me. So i'm waiting for a few days of nicer weather to tackle this. some say, hell with it and jsut unbolt the u bolts from the old rear end and put it in. I'd be interested in that but it needs the dust shields replaced, so I'm still taking out the axles to do that and having to remove the cover and such.

Decisions Decisions.

 

It it were me id switch in both 3.43s for now until maybe you can find another 3.73 front end to go with you g 80 rear end. Just because i wouldnt even consider messing with gears, sound like alot more tools and knowledge then i have