OK, i have my 89 rs with 3.08s.
I bought a complete 94 or 95 4th gen rear with posi and 3.42's.
I don't want to bolt in the forth gen rear (Don't want the bowlegged look).
can i simply swap the pinion gear, ring gear, and carrier units with each other?
with the axels still work?
what is ment by different series gears?

Thank you ahead of time for your time and patience. I tried the search function, too confusing, figured better off to ask the direct questions. I plan on doing this swap after christmas.

john

 

noop your fourth gen rear has 30 spline axles and your 3rd gen is a 28 spline.The carrier itself will bolt in fine but youd need some 30 spline axles to fit your 3rd gen diff.If ya surf through ebay theres lots of used posi diffs for your car though and there not expensive.

 

Are you sure that 4th gen rears are 30-spline? I had always heard that they were 28-spline. A lot of people on this site are running 4th gen drop outs from SLP, and I can't see them doing that if the axels don't interchage.

Your car ('89) is a 28-spline, so as long as the carrier you have is 28-spline you will be fine. The ring and pinions will swap, but you need to go through the gear setup process to ensure proper pattern and backlash.

 

4th gens run 28-spline axles, not 30.

 

silly me im thinking of the 8.5" sorry

Using your factory shims from the 3.42 gearset should put ya right in the ballpark for backlash

 

Yes, definately try the gears with the factory shims first. Check backlash and run your pattern. If all is well you're good to go. If not you'll have to adjust.

BTW, not all 8.5" 10-bolts have 30 spline axels. I found this out the hard way. I have an 8.5" 10-bolt in the rear of my '87 K5. I built it up after it broke with a Detroit locker and a Warn full floating axel kit. The axel kit only comes with 30 spline axels, of which I was unaware, meanwhile my Detroit was set up for 28 spline shafts. I had the gears all set up and ready to go, went to install the axels and they wouldn't go in. I wound up having to pull it all back apart and exchange my Detroit for one with 30 spline side gears. Now it's got the good 30 spline parts, but it was a hard road to get there.

 

ok, i am getting confused here. a couple of questions to straighten things out.

Are we definitely sure that my 89 rs with 3.08 is running 28 spline axels?

are there any pictures on here of the rear end tore completely down with the insides all layed out?

john

 

By '89 you should have 28 spline axels, unless the rear was replaced at some point with an older 26-spline rear. If you've got any doubts just pull one of the shafts and count the splines.

 

the stamp on the rear checks out with the 3.08 code in the manual. thats all i know on it so far.

 

Is the code for a 3.08 for the '89 model year, or is the same code used throughout? If you can verify that it's an '89 rear then there is about a 98% chance that the axels are 28-spline. The reason that it isn't an absolute is that '88-'89 was the changeover period for 26 to 28 spline axels. Depending on what plant the car came from, when it was produced, and what they had on the shelf there is a slim possibility that it only has 26-spline shafts. The only way to be 100% sure is to pull one and verify it.

 

According to most posts on this site, you have about 80% odds that your 89 car has the older (26-spline) axles. Especially the really common ratios, they seemed to have quite a stock of built up, that they used up before dipping into new production. Virtually eveyone that I can recall reporting on what they found in their grocery-cart geared (2.73 & 3.08) 89 rears, found 26 splines. So I'd say your odds are pretty good, that you'll find 26 splines too; in which case you'll need different axles to use that carrier. I'd recommend Superior axles; part # EV10-4

You can't tell about the axle splines from the "codes".

 

Good to know RB. Most of the cars I've done have been 3.42 rears with limited slips, which would explain why all but one were 28-spline axels. Maybe I should have hung on to those 3.42 gears and stock posi units. Sounds like there's a demand for them. They all went in the trash, repalced by Auburns, Eatons, or Detroits and 3.73s or 4.10s.

I will second that recommendation for Superior axels too. That's all I run now. My Camaro has them, My Jeep has 1-piece conversion axels from them, and I just got a set of cutom 30-spline front shafts (inners and outers) for my Blazer set up to run the 297X u-joints. The quality is the best in the business, and the price is reasonable. Plus they can custom build shafts to order with fairly quick turn around time.

 

dang it

 

so if i find a 90-92 rear in the salvage yard, i can build that up and drop it in then right, and the axels will fit properly?
does v-8 or v-6 matter?

john

 

Nope, the rears are all the same inside a particular model year.