There is ONLY one way to be sure what is in there and that is what B59 and 69Cuda said. Cost: One gasket and some gear lube.
Here is what that link says:
"If it takes
about 2 and three-quarters turns, it's
around a 2.73 gear ratio. If it's a
little more than 3, you have 3.08s. If it takes
about 3 and a quarter turns of the driveshaft, you have 3.23
or 3.25 gears.
Very close to 3 and three-quarter turns, 3.70
or 3.73 gears. This method
won't work very well on a posi that's worn-out and won't spin both tires equally"
Agree, there are ways to be close. With a friend, some tape, a jack, some jack stands, mark your driveshaft and mark your tires and you are all set to estimate. That can be suffice for many.
Not sure if the "we don't guess, we test" adage, by Hot Rod Jerry, would be satisfied.
