[Oldsmaniac]

The tag on the rear means you have a posi-traction or limited slip rear differential. This is a good start and turning the wheel and counting driveshaft rotations while in neutral will give a pretty good idea of your rear gear ratio....do the test a few times. You came up with 2.5 turns with one full revolution of the wheel. That would indicate a 2.56 to 1 ratio....there may also be a number stamped on the rear axle housing. The shop manual would convert that number to the ratio you have. It also will show location of the stamp.