As you guys know, I'm replacing the rear in the '92 Blazer.

The trouble is that it is a G80 locking rear and the debate over synthetic/dino oil and additive/no addititve is all over the place.

After reading a zillion different forums, and talking to my friend at the Chevy place, I am no closer to a definitive answer on this.

G80 is a build code RPO and seems to mean different things in different years and on different vehicles.

So I need a definitive answer on a '97 Tahoe G80 (the donor car my new rear is from).

Anyone have a manual for that year?

Anyone?

good luck on your search

Thanks, Loki.

A friend on another site just posted the '97 Tahoe owners manual and it calls for 80W90 GL5 gear oil and doesn't mention the additive.

Hope that's right.

Sounds right to me, actually Camino.

Chris

You'd be surprised at the range of opinion around the net on this.

I'm going with the manual, at least for now.

TSB 76-02-02A from Oct. '98 has a rear diff fluid chart, part of it states:

(After listing the F, Y, B/D, and GMT800 platforms)

"All other limited slip or locking differentials including C/K (non-GMT 800), S/T, M/L, G trucks: Use Only GM P/N: 1052271. (Do NOT add Limited Slip Additive)"

FYI, The GMT800 also does not call for the additive, just lists the P/N 12378261 75w-90 Synthetic Axle Lubricant instead of the P/N 1052271 80w-90.

I would go Syn for sure.

I'm going from dex III to Dex VI when I change the wife's ATF on the Cav.

With the wear and tear of city driving, I feel the syn is worth it.

I think the same way about gear oil too.....

According to what I've found, it would be a mistake to use synthetic in any pre-'98 rears as it will eat the seals.

According to what I've found, it would be a mistake to use synthetic in any pre-'98 rears as it will eat the seals.

Time to upgrade the rears?

Time to upgrade the rears?

Well, I'm upgrading from a broken rear to one that isn't.

But no, I'm sticking with the Dino oil since the replacement rear is a '97. As for the front, why fix what isn't broken?

Well, I'm upgrading from a broken rear to one that isn't.

But no, I'm sticking with the Dino oil since the replacement rear is a '97. As for the front, why fix what isn't broken?

Very true....

I would change the gear oil in the front diff & transfer case if it uses it or the proper ATF . Just my certified :twocents: fwiw. They all have seen the same mileage & abuse plus the big BANG. Lets get the debris out of the units.

I would change the gear oil in the front diff & transfer case if it uses it or the proper ATF . Just my certified :twocents: fwiw. They all have seen the same mileage & abuse plus the big BANG. Lets get the debris out of the units.

That thought has crossed my mind.

Even so, the front diff has only seen a tiny percentage of the use the rear has.

That thought has crossed my mind.

Even so, the front diff has only seen a tiny percentage of the use the rear has.

I take that it's a part-time unit then

I take that it's a part-time unit then

Most definitely, full-time 4wd was never a good idea. It wore parts terribly and killed fuel economy, only a dedicated AWD system works well enough in those categories to be viable. The domestics toyed with full-time 4WD in the 70s, and it was a real loser - many of those vehicles were converted to part-time.