Well, with the jackstands under the car so the rear wheels are in the air and the driveshaft removed from the rear yoke (leave the front end in the tranny unless you want a big nasty puddle, and make sure you don't loose the caps off the u-joint that are no longer in the yoke, use masking tape wrapped around the yoke and the end of the driveshaft to keep them on), first turn one of the wheels either direction and see what the other wheel does. Chances are, it's either not spinning, or going in the opposite direction, you most likely have a single trac rear end, meaning, if you do a burnout, only the right rear tire will spin, aka a peg leg. Now, you need to line up your yoke on the rear end in a manner that you can see and be able to count it's rotation in relationship to the rotation of one of the tires. Most likely crawl under the car from the driver's side so you can put your knee up against the driver's side tire. Make a mark on the inside, or the tread side of the passenger side tire so that you can see it when it comes around again. What your going to do is turn the yoke and count the number of times it rotates to the one rotation of the tire. Lightly put your left hand on the pass. side tire and turn the yoke with your right hand. If the yoke goes around 3 times, you have a 3.00:1 rear gear. If it goes around about 2 3/4 times, you have a 2.80:1 gear, or if its 3 1/4 times, a 3.25 gear. A 4.11:1 would be about 4 1/8 times.