Ok, here's the deal: I know a guy selling a rearend from a camaro for dirt cheap. Has everything I want: 3.42, posi, etc. Only problem is, it has the old 26 spline axles whereas the non posi differential on my firebird has the 28 spline. I was wondering if I could take my axles out of there and bolt them into the 3.42 posi. If I can, how hard is that to do?

 

Also, is there an easy way to tell by looking inside the differential housing what gear ratio I have and if it is posi or open? I'm not really sure what I have. No RPO codes or anything... very frustrated.

 

No, you cannot use 28 spline axles with a 26 spline posi unit, or vice versa. But you can put the axles and posi unit into your housing.

Stamped onto the ring gear should be a number like 11:41. You divide the first number into the second number to get the ratio. In my example 41 divided by 11 is 3.73's.

 

You need a 28 spline posi to use the 28 spline axles.

 

I personally wouldn't worry about the spline count. If you can pick up the rear for as cheap as you say, and 26 spline axles is the only downside, I'd say go for it. I've used both 26 and 28 spline rears, and never had a problem with either of them. You'll break the carrier or the ring/pinion teeth before you ever shred the splines, or snap an axle.

 

Thanks a lot you guys! I had to cut into the bolts, but I finally got my cover off and found out that I have 3.23s and its an open diff. This guy on craig's list is selling me that back end (no drums or control arms but otherwise complete) for $100. The ring and pinion gears alone are worth almost that much. And if I blow up that rear end I can always just drop a good posi carrier into the one I have on their already and be good to go almost over night.

 

Yea, I'm doing something simular right now too. I scored a wrecked & stripped '88 Camaro for 100 bucks, pulled the rearend, rear hatch glass, bumper & both doors, then scrapped the shell of it & made 30 bucks AFTER taking out for the gas I used to haul it. So the rear end was a 3.42 (ten thousand times better than my 2.73) Then Saturday I found a brand new Auburn posi for 28-splines on Craigslist for $75. So I'm gonna put together the wrecked car's housing & gears with the posi, then have to put my '91s 28 spline axles in it. Should make the car a whole lot more fun... Then add my almost free Vortec heads to the mix & go act stupid...

 

Nothing quite like throwing together a cheap muscle carout of spare parts, eh?

 

hey, so my question is... I work at a salvage yard which has a posi unit out of a 4th gen Camaro I can get for fairly cheap... also I own a 87 iroc-z with the 2.72 ratio and I believe 10 bolt.... can I put the 4th gen 28 spline with that carrier in my 3rd gen rearend??? or is that a no-no?

 

IF you have a 10 bolt. I'd say your car probably has the 9 bolt. Better check first.


If you have the 10 bolt then you can swap the 28 spline differential into your car IF you use '90 to '92 axles AND IF the differential is the correct series for your gear ratio. If you have a 2.73 then you need a 2 series differential to work with it.

 

As just mentioned, if your car has a 10 bolt and not a 9 bolt then the posi unit will fit as they're both 7.5/7.625 diffs. You can even do the gear swap for a better ratio. The 4th gen 28 spline axles however will not fit because they are longer. Only 28 spline axles from a 90-92 third gen will fit into any third gen 10 bolt diff but aftermarket 28 spline axles are much stronger than factory ones.

As nice as a junkyard posi swap sounds, the 4th gen posi is getting old. Unless it's low mileage, the posi could be worn out. They don't last forever.

 

why not just swap the axle assembly into yours

 

In all honesty, the only 4th gen posi that's worth the trouble is the Zexel-Torsen carrier. The 97-older Auburn posi's really aren't worth a damn. They have cone clutches, and are not rebuildable. Once they're shot, that's all she wrote. Torsens are great because the carrier is all gears, no clutches to ever wear out.