Finding gear ratio?

Imlooking for a new front diff for my 90 S15 Jimmy 4WD and was wondering how can you find out the gear ratio if there are no visible markings on either the front or rear differential?

nebermind I found out that its one of the slew of 3 digit codes in the glove box. Its GU4 3.08

Look in your glove box, there is a sticker with a bunch of codes. Those are RPO codes, they tell everything that was put on your blazer. You will see one that says GU followed by a number. Tell me the number and I'll tell you the ratio. The most common is GU6 which is 3.42.

nebermind you found it. :lol:

Whis is better 3.08 or 3.49? Whats the difference between the 2 besides 0.41?

3.49 or 3.42? 3.08 will give you a higher topspeed and a little better fuel economy. The other will give you better bottom end torque.


If you change the ratio of the front you have to change the back to match.