Speedometer gear

[suki243]

K my speedometer is off and i want to fix it. it says i'm going 80 with big rigs are passing me by.

This is what i know: The car is stock, so i'm assuming the rear diff. is stock. Its a V8 auto transmission, C4. I'm going to put 17s on the car.

 

[D.Hearne]

And your question is?

 

[suki243]

how many teeth would i need on my new gear. or at least the rear diff. gears?

 

[D.Hearne]

You won't know that until you get the new tires and wheels. Just saying you're going to put 17's on it doesn't tell us anything. It's the tire's outer diameter that determines what speedo gear you'll need, plus the rearend gear ratio. The C-4 has 7 drive teeth on the output shaft.

 

[BarnStang]

http://moldyrabbit.com/liquid/speedo_gear.html
THis might get you close enough.


Had to add this one. THey have EVERYTHING & anything you could imagine for a speedometer
http://www.transmissioncenter.net/speedometer_calibration_______va.htm

 

[suki243]

Sorry for the lack of info, i'm replacing my cable for the second time, and i don't want to pull it out again to replace it when i get my new rims, so i thought it could be just put in now, calculate how much it will be off until i get the rims. So i'm not sure what size rims i'm getting yet.
Thanks for the calculator tho.

What would i input for the axle ratio?

The one i pulled out was white if that helps...
my current tire is 195/70R14

 

[StangDreamin']

Two things you need:

1.) Differential Gear Ratio! If you've got a 3.73 rear gear ratio; the number a teeth on the "driven gear" on the tranny end of the speedometer cable will be more than if you've got a 3.00 rear gear.

2.) Tire outside diameter! A 26" diameter tire will require less teeth than a 24" diameter tire.

Once you have those numbers; you can use THIS calculator.

I stole it all from THIS thread on mercurycougar.net - pretty handy!