Hey all, I have no idea what gears are in my 68, It came with 327 2bbl and a 3 speed manual, it now has a 383 and a M20 4sp. I kind of remember how to check the ratio, I think you turn the rear wheel one full rev and see how many time the driveshaft rotates, is this correct?

Thanks,
Jeff

If it's an open diff rear, make sure both tires make one full turn.

If it's an open diff rear, make sure both tires make one full turn.

Or one tire makes 2 full turns...

I get the part about rotating the tire, but how do you determine the ratio?
Thanks,
Jeff

Turn one wheel exactly two times and count the drive shaft revolutions. With a 2.73 gear the shaft will turn close to 2¾ times. A 3.73 gear 3¾ times. 4.10 just over 4 times.

You may get close like that, but the best way is to drop the cover and use liquid paper to mark your start on the pinion and on the ring gear while you count. Divide the pinion into the ring gear and thats ratio.

The way you're trying goes like this. Turn the tire and count the number of times the drive shaft turns for one full revolution of the tire. Both tires have to spin the same way. If the tires make one turn and the drive shaft makes three and a little bit, you have a 3.?? (best guess)

There's a limited number of ratios, so you don't have to get an exact count to figure it out. If you want a more accurate answer, rotate the wheels a total of 7200° and divide the revolutions of the yoke by 10.
You also don't need to rotate both wheels the same direction, if one wheel will turn by itself, hold the other one still and double the number of turns.