gear ratio, how can you tell?

how can you tell rear end gear ratio?

We're trying to figure what's in my friends truck, and it has on tag.

What is the rule for rotation on drive shaft and rotation of wheel?

I believe it goes this way. Put the truck on jackstands at the rear and take all nessesary safety precautions. Mark drive shaft with white paint or something that is easily vissible. Put transmission in neutral an rotate the rear tires.This will give you a pretty good idea as to what is in the pumpkin. i.e. 3 and one half turns of driveshaft to 1 turn of wheel is a 3.5:1 rear end. hope this helps.

does his truck have a tach? if so, you can calculate the gear ratio if you have the tire size, and a certain m.p.h at that rpm in a certain gear(1.00:1 works easiest)

has no tach.

he tried turning the wheel method, and the drive shaft turned about 1.75 -1.8 times. He has another in his garage that he wants to find out. Samething 1.75 -1.8 times.

on another site they mentioned, do this and multiply by 2. This would put him around 3.50:1
I would guess this true, or close. but I've never been on the freeway with him.

I told him to pop off the cover (it's a Chevy) and count the teeth on the ring and devide by teeth on pinion & should probably take a look at fluid and condition of gears.


thanks

Your friend's truck obviously has an "open" rear end. In this case while you turned on wheel in one direction the other turned opposite? Right?
If so multiply the turns by 2.

A posi -- both tires turn the same direction and you don't have to multiply by 2.

sounds right, thanks