raptorkingcobra

I recently purchased my 90 GT, and my speedometer is what I am guessing 15 or 20 mph off. It says I am doing 70 when I am really doing 50 to 55 mph. It has a yellow 18 tooth Speedometer gear currently. What is the easiest way to determine my ring and pinion gearing so that I may purchase the correct speedometer gear?

thanks

jzgt

One of two ways:
1. Count the number of rotations of the driveshaft flange to the rotation of the tires
2. Pop off the rear end cover, be prepared to smell like onions for a week (gear oil), spin the tires until you can see the numbers stamped on the ring gear, the end facing the rear of the car. Divide the two numbers and that'll give you your ratio.

Edit: I am assuming you have the stock rim and tire set, right?

- Jeff

nitrous_bob

18t was used w/ 2.73's and a 8t drive gear on the tailshaft.

you can also confirm your original by the doortag, "ax" code m=2.73, z=3.08, e=3.27

ds rotations for 1 complete revolution of the tire is the easiest way, chalk the ds, and chalk the inside of the tire, jack up the @ss end, and spin.

only problem is, if you have 3.73's or bigger w/ your 8t drive gear you cannot correct it w/out replacing the drive gear on the tailshaft. you can do 3.73's but have to use the 23t speedo gear, that is not a ford part even though steeda and everybody else sells them, it's from a jeep, has the wrong pitch, and will wear out quickly.

raptorkingcobra

OK, I will count the number of rotations of the DS. Once I have this number how do I calculate it?

I checked the AX code and it was an "M" so original was 2.73 if you are correct Bob.

I have the 16" wheels with 225/55's

Thanks for the help fellas, I will update ya soon.

raptorkingcobra

anybody?

2 kwik

1 tire rotation and when you see how many times the d-shaft rotates will give you your final ratio
ford raatio
2.73
3.08
3.27
3.55
3.73
3.90
4.10
4.30
4.56 and so on