Differential ratio?

The string method works on any vehicle, any tire size and note that some previous
owners (on used vehicles) change out their diff gears


2500 Suburban - How to determine ratio?
Diffratio diffratiostring diffstring

quote from above link

benk wrote:
Posted: 11/01/11 10:23am...ps...the links no longer work..buddy took down his web site


Several ways to check, but the most reliable is with an actual count.

There is a label in GM glove boxes that lists all of the options that
vehicle left the factory with. Called RPO codes and here is a link
to my buddies site with links to several RPO code sites:
http://aplsweb.com/Topics/RPO-URLS.htm
Some of those links are no longer and this one is the better of them
http://aplsweb.com/Topics/TopicPix/RPO.pdf

But, since buying used, the previous owner(s) may have changed out the
gear set.

Best to then tie/tape a length of string on the drive shaft. Note a
datum.

Then roll the vehicle one tire rev using the valve stem as a datum

Count the full turns and the fraction left. That is the diff ratio
and makes no matter what size tire or suspension lift, etc.

Remove the string.

Here are some of the codes. Note that there are some only for cars
and not for trucks


GM8: Axle - Rear (2.56 Ratio)
GT4: Axle - Rear (3.73 Ratio)
GU2: Axle - Rear (2.73 Ratio)
GU4: Axle - Rear (3.08 Ratio)
GU6: Axle - Rear (3.42 Ratio)
ZQ9 - Axle, performance ratio (4.10:1) (requires G80 & L78 or Z28)