This is waaaay overdue but I think it's about time I tackle this issue

First of all my car is a 1991 base model Firebird with an L03 and 700R4.

Back in December I did a rear end swap on my car...my car came with a 2.73 open rear end and I put in a 3.23 posi rear end...since then my speedo has (understandably) been off roughly 10mph (higher or lower depending on how fast I am going), because of the gear change.

My question is...I'd like to re-adjust my speedometer to compensate for the gear change... how can I do this?

I've heard from some places that I'll need new speedo gears inside the transmission...from others I've heard it's as simple as a computer adjustment.

HELP! Thanks...

 

You need atleast one new speedo gear if not two. I'll run the calculations later when I have more time.

 

Yes, all you have to do is replace the speedometer gear(s). They are located on the tailshaft of the transmission and on the VSS itself. Here's a step-by-step on how to replace them:
http://sethirdgen.org/vss.htm

Once you know what gears you need, just check out the FAQs on the main page for the GM part number list for the different gears. When you remove the extension housing to replace the gears, you should replace the 2 seals on it. The front o-ring seal, GM part number 1358899, and the extension housing oil seal, GM part number 8673526. If you want/need a new speedometer gear clip, it's GM part number 6261781.

 

Jungleman, where did you get your posi rear end from?

 

Got mine off eBay. I think it was $100 plus shipping (which was $150!) but I couldn't find anything local. The rear needed new rotors and pads but other than that has been problem free...actually looked less rusty than my old rear end which has spent 14 years under a NC car.