I have a 91 firebird 305 TBI 700R4 and a one leg 2.73 rear. I had been looking for a posi unit and came across one in the junkyard that was in a 4th gen Z28(I think about 93-96 roughly). According to what I have read on this site it should fit my car but I am not sure because it has this ring of teeth just behing the ring gear(see pic below) and my car does not have that on the carrier.



Can anyone tell me what that is for and whether this will prevent me from using it on my thirdgen. I know that this unit has a 2.73 gear ratio which I would be upgrading anyway since I'll be in there. I also have some other pics of the identifying marks on the unit.







Can anyone help me out with this? Thanks guys!

 

That looks like a posi and that's the abs ring you can remove it and just instill the ring gear

 

It's an Auburn. 2 series.

The ABS "tone ring" doesn't matter; you can leave it on, doesn't bother anything. There's a sensor in the pumpkin that reads it in the cars with that type of ABS.

 

Thanks for the help guys. I had someone look at it today and he said it was good but that I may want to replace the spider gears. Any threads here on how that is done? Again, your help is very much appreciated.

 

Bumping this up a bit to ask another question. I found a set of 3.23's on a car in the junk yard. They were on an 84 T/A/. Will these gears fit my series 2 Auburn unit? From what I've read here it won't work. I just wanted to verify. Thanks again

 

No, only the special thick after market gears will work on the 2 series.

 

Sorry i hate to hijack your thread but i have kinda the same question. I picked up an auburn posi at the junkyard today out of a lt1 firebird and wont to know if it would bolt right up into my 88 bird 305 TBI 700R4 and if i could use my same gears seeing how i could not get the pinion out of the lt1 car



***edit***

Damn found my answer, and no it wont work in my car with out the 28 spline axles..

 

What gear ratio was in the LT1 car and what gear ratio is in your car? That makes a huge difference.

 

the ones in the lt1 car are 2.73s and not sure of what ones are in my car

 

Then that would make the Auburn from the LT1 car a 2 series. Until you know what the gear ratio is in your car you will not know if you need a 2 series or a 3 series. You also need to know if you have 26 or 28 spline axles. The LT1 would have 28 spline axles. If you have 26 spline axles then you can't use it unless you change the axles. Your '88 should have 26 spline axles.

 

from what the stickie said my car is a 26 spline so i would have to get a set of thirdgen 28spline axles, im sure i couldent use 4thgen axles seeing how they are a few inches longer?..

 

Yes, you would need a set of '90 to '92 axles.

 

Ok there was one of them at the junkyard i got the auburn from so my next day off ill grab them, as for the gear i think the posi i got is a series 2 by fallowing the stickie about 10 bolts and the gear ratio so if i had to could u use the pinion out of the car i got the posi from in my thirdgen rearend? or should i just get new gears?

 

You can not mix gears. They are mated at the factory and can not be mixed after they are laped.

 

Ya but if I used the gears that came with that lt1 car would.the ring and pinion swap into my 88? With the posi?

 

Yes, if you use the ring gear and the pinion gear from the LT1 car they will fit your '88 rear end. You must set the pinion depth, bearing preload and backlash when changing gears. It's not a simple bolt in job. Gears must be set up correctly or they will make a lot of noise and probably wear out quickly or break.

 

Damn figured it wouldent be that simple how would I go about doing that if u wouldent mind explaning.. guess i should see if my gear would work on it first im pretty sure my gear ratio is 2.73 open diff. would it bolt to the auburn?

 

If you have a 2.73 then it will work. Read this. http://www.nastyz28.com/forum/showthread.php?t=19773

 

So I would.have to check the backlash on the ring in my car first before I would bolt it.up to the posi? Damn and when I was pulling it at the junkyard I was thinking it was going to be an easy job.. guess I better do a Hell of a lot more research before I jump head first into anything like.this again