Hope this isn't such a stupid question. How does one tell what gear ratio is in his/her Blazer?

 

Jack up the rear end and put it in neutral. Mark the driveshaft with something like liquid paper. Get a friend to help and each of you simultaneously spin a rear tire forward one complete turn. Note how many times the driveshaft turns. If it turns just over three times that would be a 3:08 ratio. Just under three and a half turns would be a 3:42. three and three quarters would be a 3:73 etc...

 

Or check your RPO codes in your glove box (2nd Gen) or elsewhere. Not sure where they are on a 1st Gen.

GU6 is 3.42's

A quick search of "gear ratio" or "RPO codes" should yield the rest of the codes.

 

Thanks for the info and quick replies. Bandidolenny, it never occurred to me what you suggested, it's a manual / physical way of finding the answer, it makes absolute since. I was thinking more along the lines of what Tripleblackblazer mentioned, some numbers somewhere or a stamp on the axle, or at least something along those lines. Either way, great input, thanks!!! If I ever work on a really old vehicle I'll have two options now to figure out this question. Thanks again!

 

You are welcome. Also, the next time you are changing the diff fluid and have the cover off, look for numbers stamped into the edge of the ring gear. You will see something like 41:12 . The first digit is the number of teeth on the ring gear, the second digit is the number of teeth on the pinion gear. If you divide 41 by 12 you get 3.41667 or what we call a 3:42 gear ratio. Just another way to do it...

 

Cool! Thanks for the additional info, it's nice to know.

 

This should almost become a DIY or FYI reference! Nice!