gear ratio identification
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Senior User
Joined: Jan 2006
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From: Little Falls,New York
gear ratio identification
Ok,I've heard different versions of this and most end up in" find the reciprocal of the derivitive of the square root of the 
.Is there an easy way to tell my gear ratio of a nine inch ford out of the vehicle on stands?
.Is there an easy way to tell my gear ratio of a nine inch ford out of the vehicle on stands?
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
If you have a limited slip axle you need both sides up on jackstands, but it's easier to do it with one wheel in the air and one on the ground with an open differential.
With a limited slip (both tires in the air) turn the wheel one full rotation. The number of times the driveshaft turns is approximately the gear ratio.
With an open differential (one tire in the air) turn the wheel two full rotations and count the number of times the driveshaft turns.
Sorry, but short of getting the tag or the axle code off the doorpost there's no easier way to do it. It's as easy as I could make it for you.
With a limited slip (both tires in the air) turn the wheel one full rotation. The number of times the driveshaft turns is approximately the gear ratio.
With an open differential (one tire in the air) turn the wheel two full rotations and count the number of times the driveshaft turns.
Sorry, but short of getting the tag or the axle code off the doorpost there's no easier way to do it. It's as easy as I could make it for you.
Super Moderator
Joined: Apr 2004
Posts: 34,481
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If it is out of the vehicle, count the teeth on the gears and divide.
Look in the carrier--do you see only spider gears, or do you see some plates/springs etc.
Pics here:
Currie Enterprises Racing Rear End Categories
Look in the carrier--do you see only spider gears, or do you see some plates/springs etc.
Pics here:
Currie Enterprises Racing Rear End Categories
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Try to spin one wheel while the other is in the air. If both wheels spin in the same direction it's a limited slip. If it spins in the opposite direction or if the pinion spins it's an open differential.
