Thread: rear gear ratio

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I'm sure that this question has been asked before but here goes. Without counting the teeth on the ring and pinion is there a way, by counting the revolutions that the tire and the drivehaft make, tocalculate the gear ratio?

OK, one more time. Jack up one rear wheel if its an open (Non-posi) rear. Turn the wheel TWICE and count the turns the driveshaft makes. If its a posi, jack up both wheels and turn the wheels ONCE.
Three turns of the driveshaft=3:1 gears.
Its east to tell the diff. between, say, 3.08 and 3.23 . Its helpful to know the possible ratios offered in your vehicle to help decide which you have.

Don't forget to put some sort of easily seen mark on the driveshaft and count carefully; we just used a white paint mark. I recently had a friendly argument as to whether I had a 3.55 or a 3.50 ratio and we ended up jacking up one rear wheel (non-posi) and rotating the wheel 100 times before we were sure I have a 3.55 8" rear. I knew the 8" came in 3.55 gears but the garage guy is used to using 3.50 in the 9" rear so we had to check it out after the argument came to a certain level of stubborn disagreement.

Don Shillady
Retired Scientist/teen rodder

That's exactly why I suggested having the possible ratios at hand, so you know one is pretty close to what you count.