I recently blew up my rear end in my 85 Iroc. I pulled the gears and put in some other ones I had to buy some time, now it is tore apart again and it is time to put ones I want back in it. I found that the gears that I blew out were 3.73's, and I believe that my car came with 3.23's from looking at the production codes chart on this website. I cannot find any of the numbers on the axle housing on the rearend. The only numbers I can find are on the gear housing. I wanted to know if I have the 26 or the 28 spline (axles I believe). If anyone has any ideas please let me know. I also am looking for a set of 3.73 gears and possibly a posi unit to put back in it. Let me know if you got anything. Thanks!

 

Unless someone has changed the axles, 82-89 will have 26 spline.

 

The RPO codes wil identify the stock gearing.
Do you know if the speedo is off or not?
If you havent identified the gear ratio, there are the numbers on the gears usually. Most companies do like GM does and have the dividing numbers. Like 41:11 would be 3.73s. Also GM puts a part number on theirs and ususally has stapmed on the ring gear the differental those are for. Like 7 5/8 for the 7.625 diffy. Sometimes thats fractional and sometimes its in decimal form.