Hi,

I bought a 94 3.4l V6 Camaro recently, and while driving it home I noticed that, among other things, the speedometer was way off.
I had to use the Google Maps on my phone to get my actual speed to avoid confrontations with the law.
I have no idea what the previous owner has done, but the speedometer shows 60MPH when driving about 40MPH, and 90MPH when driving about 70MPH, and so on.

I was looking around this and other Camaro forums without finding any real tips for how to fix this?
Is there any way to calibrate this, or does the transmission need an overhaul?

 

Sounds like your rear end was swapped at some point.
Jack the car up and spin the wheels to determine what ratio you have then compare that to what the option code on your door says.

 

Tires may also be part of the cause if they are not stock height.
A speedometer shop should be able to calibrate it for you.

 

Thank you for the replies.
I posted the same question in another Camaro forum and found some info on how to tune the PCM based on my tire size and how off the speedometer is, so now I'm just awaiting the postman to come with some OBD1-USB cable so I can get started.
I'd rather do it the geeky tuning way than the I-need-to-tear-down-the-entire-rear-of-the-car-including-the-transmission-to-perhaps-fix-it-or-just-ruin-it-and-then-hate-my-own-reflection-for-the-rest-of-my-life kind of way.

Attached is a great excel-calculator I got while looking for fixes to this problem

 

probly should (if you havent) pull the speed sensor on the transmission and see if you have gears or reluctor. if you have plastic gears then you will need to change to different gears to match tire size and rear differential gear ratio.

 

I live in an apartment, so I don't really have any room to pull out the entire transmission to change gears.

 

you dont pull the trans, you just pull the speed sensor. its at the back of the trans on the driver side.

 

look at 20 here 4th Gen LT1 F-Body Tech-Component Location Views

 

Wouldn't I need to drop it to change gears?
It was my understanding that the driving gear was located on inside the tail extension

 

The driving gear is on the output shaft of trans.
The DRIVEN gear for speedo/reluctor is shown at the website posted - Vehicle Speed Sensor.