Chevrolet Repair: gears, diff gears, gm product

Question
How can I tell what gear ratio I have?

Answer
Hi Mike,
If you have a GM product, there is a decal, usually in the glove compartment. Has a whole bunch of three character codes. Those are called the regular production options, or RPO codes. That tells everything that was installed on the vehicle.

Then go to Google, and enter RPO codes, and you will get a bunch of sites.

Diff gears usually start with G, like G87 etc. Then look it up.

If you just have a diff, and dont know what it came in, you can remove the cover, and it will be stamped into the ring gear.

You can also mark a tire, and the drive shaft. Roll the vehicle till the tire rolls one complete revolution, while watching the driveshaft.
If the driveshaft turns just a tiny bit more than four turns, to one of the tires, it is something like 4.11:1, commonly referred to as a 4 11.  Or if it turns 3 and 3/4 turns, it is like a 3.73:1.

The more accurate you are with your marks and measurements, the closer you will be.

Van