I've read, you jack up the truck put a piece of tape or chalk mark on the drive shaft at the rear universal joint, a piece on the rear wheel and rotate the the wheel 1 full turn and count the rotations of the tail shaft, for instance 1 turn of the rear wheel = 3 turns of the the drives shaft = 3:00 rear etc. well, I did that and 1 turn of the wheel = only about 1 3/4 turns of the drives shaft, now I don't think I have a 1:75 or even a 2:00 rear gear don't think they put anything that high in a a 9" ford, FYI, any ideas if I'm doing this right?
Don

 

Here is link that will help.


Ring Gear - Pinion Gear Ratio Calculator

 

I was told with an open rear, with one wheel on the ground and the other up, rotate the wheel 2 revolutions. When I had my 3.92 rear, 2 revolutions of the wheel gave me almost 4 revolutions of the driveshaft. Dennis

 

The way I was taught years ago from an old mechanic is spin BOTH rear tires by hand together and count driveshaft revolutions, never been wrong.

 

Ditto this.

 

So I did the one wheel on the ground 1 off the ground, (open rear) 2 revolutions of the wheel = 3 revolutions of the drive shaft = 3:00 rear, now have to locate the appropriate speedo gear, Thx guys!!!