Join Date: Mar 2002
Location: Austin, TX, USA
I wish I could find the web site - It had great pictures and everything. Anyway, here is a summary of the notes I took.
On the pan rail, right rear side is a number. The first digit is the model year. The first year is 1982 and oddly enough, GM stamped a 9 for the first digit. Every year after, the first digit matches the year such as 83/3, 84/4, etc. Also around 1989 the case changed - the pressure taps on the right hand side were eliminated. Some 1989 cases have them and some don't. The year designation causes a conflict in numbering. 1989 and 1982 models both begin with a 9. If the case has taps, then it's an 82. If it does not have the taps its an 89.
In 1987, a major upgrade was performed. The upgrade included a 10 vane pump, 30 spline input shaft, auxillary valve body, and a 28 element sprag. One way to tell if your transmission has the upgraded pump, is that the last three digits on the pump are 732.
Hope that helps. If anyone has a correction, let me know. My notes look more cryptic than they did when I first wrote them.