I bought a Diff need to make sure its 3.9 before I install
 

Hey guys I bought a diff I want to make sure its a 3.9 before I install it how can I make sure? I counted the teeth and my 4.10 had 41 of them. Now I counted the teeth on the 3.9 I just bought and it had 43 of them is this correct? Or did I buy a 4.33 :Kill1:

Give the input shaft a 360 degree turn, how many degrees did the output shaft turn?

Yeah, mark a tooth on the ring gear, and one on the pinion. Spin the ring gear 1 full turn and count how many times the pinion turns around. 1 full turn of the pinion to 3.9 or almost 4 turns of the pinion, and you've got a 3.9:1

Ring gear teeth divided by pinion gear teeth give you your ratio...

Divide the number of teeth on the ring gear by the number on the pinion
J

If it has more teeth then my guess is you have the 3.9. Why go with the 3.9 anyways?

4.10 = 41/10 (ring gear/pinion gear)

3.90 = 43/11

cough cough ls1 :)

-dj

Thanks Jim that makes it easy.