[alexbrown64]

You dont have to drain your fluid and remove your cover. I found this on the net and its easy and accurate..

The easiest way is to chock the other wheel if you don't have an LSD, if you do have an LSD you don't need to. Mark the wheel and shaft in the same way, then turn the WHEEL not the shaft. Turn the wheel 10 times and count the shaft revolutions. For a 3.73 diff, with a none LSD the shaft will turn just over 18.5 times (18.65). Multiply by 2 which gives you 37.3. You have turned the wheel 10 times so you need to divide by 10 giving you 3.73. If it's an LSD axle then it will turn 37.3 times, so go straight to dividing by 10

Cheers,