finding my Gear Ratio ?????

[gmcjimmy88]

I realize the best way to determine gear ratios is by removing the covers, but isnt there another way? I thought I read somewhere that you can rotate the yoke and count the axle spins to get a rough guess. This could be backwards or completely wrong that is why I am asking here. Is there a way to guestimate gear ratio without taking it apart? Something that could tell me a difference from say a 4:10 and a 5:13? I realize it wont be perfect unless the covers are removed but hoping I could get an idea before purchasing. Thanks for the help and hopefully answers to my questions.

 

[1987Chevy]

If you have an accuate tach, and spedometer hooked up and know your trans gear ratio thirdgen.org has some calculators which I was able to use to be about 99% sure that I have good old 3.08 gears.

 

[gmcjimmy88]

Well I am purchasing rear diffs that are in a running truck. Thanks though

 

[ryan22re]

pull the cover look for the marks on the ring gear.

41 11 would be 41 teeth on the ring gear and 11 teeth on the pinion and a 3.73 ratio.

 

[Trigger Creep]

I found these on this site earlier today.

http://pitbulltires.com/calculate.php

 

[3 on the tree]

My way; both tires in the air. If the shaft is still attached, make a mark on it. Make a mark on the tire, or axle flange. Turn the shaft or yoke 1 complete rrevolution. Count how many times the tire rotates and multiply by 2. Its not very precise, but you will be able to tell the difference between a 3.07 and a 4.10.

 

[Dallin]

If it is an open differential:

Jack up 1 tire (make sure other tire doesn't move)
Spin the tire 2 complete revolutions (tranny in neutral if connected)
Count the number of drive shaft revolutionsl. This is your gear ratio.

3 & 3/4 revolutions = 3.73 gears
4 & 1/8 revolutions = 4.11 gears

If you mark lines on the tire and driveshaft you should be able to do this accurately enough to determine any gear size. Okay, you can't tell 4.10 from 4.11, but 3.73 from 3.40 is no problem.

 

[gmcjimmy88]

Those are the way I was thinking but wasnt sure. Thanks for the assistance. I will try it out on my truck here so I know what I am looking for up there thanks again.