......I just picked up an 89 GTA from an auction. The speedo is off. I have confirmed the gear ratio to be a 3.27 which is original. Tire size is 245/50/16 which is also standard. This must mean a tranny swap at one point in time. The tranny in there is a 700R4. My question is does anyone know what the GM part# is for this application. I would like to order from GM parts direct as long as I know what to ask for....

 

https://www.thirdgen.org/newdesign/faq/thirdgen.shtml

The part numbers are in the "tranny/ rear end" section, about two-thirds of the way down the page.

Just a little above the driven gear answer, is how to find the right speedo gearing for your application.

Hope this helps.

 

...its a good article, but I have read through it once and unless I missed something it tells you how to calculate your speedo/drive gears according to a rear end gearing change based on the premise you already know the speedo/driven gear combo. In the example they list they use 2.73 gears which use 17 tooth speedogear to 37 tooth driven gear. It also shows some rear gear applications but does not list the 3.27 rear that I have. What I need to know is the correct driven gear in the tranny as all else is stock on the car. Thanks for the link however, its nice to get a little help on this.