I bought a posi unit and i want to know how can i tell what series it is? Id like to know what kind of gear i can put on this before i open up my rearend again.

 

I think you should be able to tell by the thickness of the mounting surface of the ring gear. Or you can check the part number that is stamped on it. To be honest, those are just guesses, but i know the distance of the ring gear mounting surface is the determining factor.

 

If you want to know without opening it up, then look for tags bolted on with the pumpkin cover. They should clearly state the gear ratio and an additional one will be there to indicate positraction. 3.08 and smaller is considered 2-series. Above that is 3-series. There is a 4-series, but you won't have that.

If you can't find any tags, then look for a code stamped into the front of the passenger-side of the axle housing. Be careful not to scrape the code off when you are scraping all the greese and dirt off. It is large, but not stamped very deep. Post the code here and we can decode it.

Of course, if someone has already modified the rear, then you will have to open it up and peer inside (which is not difficult). Just get a bucket under the thing.

 

I have a stock differential that came in an S-10 with 3.73 gears. It measures 1 31/32" (almost two inches) from the ring gear mounting surface to the outer edge that goes into the bearing. It's good for 3.23 and up. there is usually about 3/16" difference from one series to the other.

 

Thanks Jay. It looks like mine is just under 2 inches from the outer edge of the hub to the mating surface of the ring gear... the mating surface for the ring gear is about a half inch thick... have you got yours handy to measure that? Thanks

 

Ok, so by "unit", you mean carrier?

Then just copy down the model number and call up the manufacturer or dealer to find out the specs on it. I did that once for a Zexel Torsen I had and the support people were more than helpful.

 

Yes , the stock flange is 7/16" thick. The Auburn differential that replaced this one had thicker flanges but it's installed.