how to check gearing?

[288sunny]

Well my jeep came stock with 3.73 gears and thats what i thought was in there, and they may still be, however im alittle thrown off, because i changed out my speedo gear because it was off about 4-5 mph, the gear i took out was a 36, the jeep had 33" tires on it and a 36 speedo gear with 33"s matches up to 4.56 gears??? Jeep also ran very well for having 33's, but speedo was off.. i went to a 31 gear and still have the 33's, speedo seems to be about dead on, but now im really curious??
Also it is possible because the guy i bought the jeep from had new yukon axles installed and a lunch box locker. So my ? is how could i find out exactly what gears it has to be sure?

 

[Bounty__Hunter]

Jeep Speedometer Gears at Morris 4x4 Center

Most charts show a 36t for your stock application, 3.73 gears and 28" tires. It also shows a 31t for 3.73 gears and 33" tires, so it sounds like you're correct on having the 3.73 gears.

To be sure, you can pull the diff cover and look for a pair of numbers etched on the outside of the ring gear. This pair of number is the tooth count of the ring and pinion. Divide the larger number by the smaller number to get your ratio. There may also be a part number and/or serial number on the ring gear, but you want the pair of numbers, usually something like 41 10 or similar (4.10 gears).

Many will tell you to jack up the rear axle and turn the tire, counting how many times the driveshaft turns. This isn't precise enough for me, don't trust it.