Speedometer Gear

Axle Ratio 6T 7T 8T- Drive gears

Driven gears

2.73 - 16 18
3.08 - 18 20
3.27 16 19 21
3.55 17 20 -
3.73 18 21 -
4.10 20 - -
4.30 21 - -
4.56 - - -
from D&D performance www.ddperformance.com

It's not likely that you will get it exact. My '93 SSP (with AOD) now has a 3.73 rear end. On the stock SSP tires (26" dia.) it would need a 23.2 tooth speedo gear. That's a 0.8% error. Right now, I have 25.6" tires on it, which requires a 23.7 tooth gear, which is a 3.0% error.

23 is as close as you can get (duhhhh). If you want to get the speedo right on, you'll have to adjust the tire size.

Chewed-up 23 tooth gears are normal. The teeth are very thin and break easily. I buy replacements two at a time.

Changing to a 7 tooth drive gear will help, but depending on your tire size, you'll need a 20 or 21 tooth driven gear. You could still see an error as high as 3 percent if you're in between the two sizes.

And don't forget, the speedometer itself could be off a little too, compounding the errors in your indicated speed. I believe speedometers can have an error as high as 5% when leaving the factory. The SSP's "Certified Calibration" speedos had to be within 2 or 3% at all speeds. (I'm sure someone will let me know if my numbers are off.)

On some model years, it's not easy to change the driven gear, because it's machined as part of the tailshaft.

Good luck.