Determining rear end gear ratio.

Aug 14, 2004 3 Replies

Hi:



The rear end gears in my '64 1/2 are far too high ratio for my taste. The engine's revving higher than I am comfortable with at as little as



50 mph. My father put the gears in originally and I remember quite clearly him saying that they were 4.11's. That would seem about right considering the low end power the car has, but not consistent with his nature (I can't imagine why he would put street gears in it). I would prefer something more comfortable, since I would never race the car, or anything similar. This weekend I grabbed another rear end my father had lying around.

The problem is, now he doesn't seem sure at all about the history. He claims now that maybe the gears in it are the original 2.73's, and maybe it's the non-original tranny (apparently pulled out of a Granada) that leads to the high low end gearing. My knowledge of this is limited, so I have no idea how reasonable that would be.



The question: is there a way to determine the ratio on the gears currently in the car, without pulling things apart (e.g., are there markings or something)? Furthermore, am I right to assume I will be able to determine the ratio on both the new and old gears simply by counting splines (pretty sure, but why not ask)?



Thanks.


What gear ratio do I have? Jack up one tire if you have an open differential(diff), or both tires if you have a limited slip or locking diff. Put the transmission in neutral. Rotate the tire one full revolution for limited slip and locking diffs and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

Do I have a limited slip or locking differential? Jack up both tires. Put the transmission in neutral. Turn one tire. If the other tire spins the opposite direction you have an open diff, and if it spins the same direction you have a limited slip or locking diff.

Some good information on this subject is given @

Thanks! No posi though.

And she's beautiful, BTW.

The transmission is not the problem, unless it's not shifting to high gear.

Al

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