How can i tell what rear end i have in my 02 Blazer?

Pick up the phone and call the local "bow-tie" dealer, and ask for service. Give them your VIN, and they will tell you. Of course, that rear end could have been replaced some time ago.

After you call the dealer and they give you the axle ratio,do this test to verify whether what gear they told you was installed,is still installed(just in case you're not the original owner.Jack the rear wheels off the ground,use chalk or witeout and make a mark on the sidewall of tire at the 6 oclock position.Now make a mark on the center of driveshaft.Take the transmission out of park and put into neutral.Slowly turn the wheel one complete revolution while noting how many revolutions the driveshaft makes.So if the driveshaft turns 4 1/4 times,that gives you around a 4.11 gear ratio.If it turns 2 3/4 times,that would be a 2.73 ratio.Another more precise way to calculate ratio is by dividing the ring gear tooth count by the pinion gear tooth count.So if the ring gear has 37 teeth and the pinion gear has 9 teeth,that comes out to 4.11 gears.Some vehicles have a metal tag bolted to the rear end cover or housing with the axle ratio stamped onto it.

Check the drivers side door. Sometimes they put that info on the doors. Otherwise, you can call a Chevrolet dealer and give them the VIN number and they can tell you what rear end was put on the vehicle when it was built. Keep in mind that unless you bought this vehicle new, it is possible the rear end could have been replaced with another one with different gear ratios.

Take the VIN code to any Chevrolet Dealers parts counter. They'll be able to tell you the final drive ratio within minutes.

there will be a metal tag on one of the bolts of the rear end cover, this will give you the info you need

It should be stamped on the front of the passenger side axle tube.