I found the where the number is on the rearend. But where do I find out what kind of rear it is. Or is anyone can tell me. The number is 22522678. BTW it is off of a '91 Z28, has posi, and 3.73 gears. It was also recently rebuilt.

 

People post that number every couple of days, hoping that it will unlock some great secret of the universe. Unfortunately, it is basically useless. It is the casting number for the center section of the typical stock rear end housing in one of these cars. It tells nothing whatosever, except that it's a 7½" 10-bolt.

 

cool...thanks. I wasnt sure if was anything special or not....

 

so no # at ALL (driveshaft, rear end) will tell u if u have posii or not. i ask this bcuz a salesman where i work bought an 84 firebird with a 305, and when he was at advance auto parts or auto zone (i don't remember what one it was) they looked up his car and was like "o ya, u have posi in this" but never told him anything else. so i guess they are a bunch or idiots?

 

i believe the number you're talking about is on the passenger side axle housing facing the front(that's where it was on mine). i think that number will tell you whether the rear was posi and what gears it had originally, but the only reliable way is to just physically look. If you KNOW it's all original and hasn't been messed with, then just look at your rpo's. i know gu6 is 3.42 gears, g80 means it's got a posi rear end. in that case just run your rpo's on the rpo decoder found off the main page

 

my RPO says GT4 : AXLE REAR, 3.73 RATIO
so does that mean i don't have posi?

 

no thats just gear ratio... g80 means posi i think

 

so u're saying that the posi RPO is separate from the gear ratio RPO?

 

You have seperate RPO numbers for the options. For the Rear gears RPO G-- and
for the Limited slip (aka Posi) RPO G80. Also a another RPO for the Rear brakes (drum or disc). Every option has a RPO number.