maybe someone can tell me just by looking at it, but I haven't been able to find any info other than the 3 series is thicker. so without have a 2 series to compare it to, I don't know what I bought.

 

Well, I don't mean to be smart about it, but you bought something that I would have tossed in the scrap metal pile. Whether it's a 2 or 3 series, a used Auburn is usually trash. It looks like a 2 series to me. A look at the other end would be more helpful.

 

might be trash, might not be, but it was cheap and is supposed to work. If i tore it open would it be obvious if it was messed up? here are some pics from other angles.

 

Looks 2 series to me.

Agree w BGH; that's not a real logical way to approach buying parts. (a) not knowing what series it is, and (b) paying money for something that's hardly ever in actual working condition, usually doesn't turn out well. Instinct tells me you'll find you have just taken money out of your wallet and turned it into dumpster ballast, in one eeeeezy step.

That said, here's how you can tell. Here's pics of a coupla those POSs side by side; 3 series on the right. Note how the back side of the ring gear flange is kinda cone-shaped, where on the 2 series it's kinda more flat; that's because the 3 series ring has to be located around .400" or so closer to the pinion than the 2 series.



If you can get your money back, I'd strongly recommend it. Otherwise I'm afraid you just made an unnecessary optional voluntary installment payment on the "hot-rodding education tax".

 

And of course, if that gear sitting next to it came off of it, a quick glance at the ratio stamped on it will tell you everything you should have looked at before buying it. If I was the betting kind, I'd bet it has either "41:15" (2.73) or "40:13" (3.08) stamped on the edge somewhere.

 

nope, ring gear was mine already. it's a 4.10. this posi carrier is a 26 spline, but it came without a gear, thus i had no idea if it was a 2 series or 3 series. I don't see any cheaper way to get my gears and a posi in my car than with this carrier and a spacer using the gears I already have, since any other style of posi will require me upgrading to 28 spline axles as well, and at that point it seems like i should be seriously considering just replacing the whole rear end with something better.

 

If you are planning on using a spacer on that then you are asking for big trouble. The 7.5 differential doesn't have a tall enough band around it to hold the ring gear centered when a spacer is installed, so the ring gear will just be floating around until you get the bolts tight. Then it's not going to be centered and it's probably going to move around under power. You would be much better off getting one of the thick gear sets that are made for the 2 series differential. Ring gear spacers are always a bad idea, but especially bad in the 7.5 rear end.

 

so what you are saying is just ditch what I have and buy this?

http://www.ebay.com/itm/NEW-Eaton-locker-posi-unit-3-series-7-5-7-65-10-bolt-26-spline-ss-camaro-z28-/290957210525?pt=Motors_Car_Truck_Parts_Accessories&hash=item43be66b39d&vxp=mtr
lesson learned.

 

There are thick 4.10 gears available for the 2 series 7.5 differential. If you want to use the differential that you have then get one of them. If you want to use the gears that you already have then get a 3 series differential (something other than a Auburn). A ring gear spacer is going to cause you trouble in this rear end. DO NOT buy the differential in your post above. That is a Governor Lock, and it can be even worse than the used Auburn. They have it listed as a Eaton Posi, but it is NOT a Eaton Posi. It is a Eaton Governor Lock.

 

fair enough. so what am I after then? the eaton posi?

 

Eaton Posi is a good one. Also look at the Yukon Dura Grip and Eaton Truetrac. A used Torsen is also good if you use 28 spline axles.