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How to verify Rear end Gear ratio dsm.

I recently purchased a car that had the Evo Gsr 64 crown tooth ring gear close gear ratio transmission. I recently was curious as to whether the car had the correct 3.909 rear end in it. So below you will see two videos of how I verified that I had the correct rear end in the car. This method can be used to verify whether you have an automatic rear end or manual rear end. I searched for days high and low and the couldn't find any way to verify my rear. the other only way to verify which rear end ratio you have is to pull off the rear end cover and count the tooth.

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Forgot to mention you need to if you are doing it by yourself place your cell phone under the car and video tape the driveshaft revolution.


Nov 14, 2013
Independence, Kansas
Since the video's are not available, I believe I can explain the process.
If you have an LSD rear dif (both tires rotate the SAME direction when turned and the car is on jack stands or up in the air), rotate one of the tires ONE FULL TURN while counting how many revolutions the driveshaft makes. If it is CLOSE TO 4 turns, you have the 3.909.
If it only turns about three and one half turns, you have the 3.545.
If it only turns about three and one third turns, you have the 3.307.

If your differential is NOT AN LSD (one wheel will spin one direction, the other side will do the opposite) then you need to hold one tire in place (get a helper to hold it still), and rotate the other tire ONE FULL TURN while counting the revolutions of the driveshaft and use the same determination as you do if you have the LSD rear.

It is a very easy way to tell any differential ratio without pulling the cover (but of course counting the ring teeth and the pinion teeth will get you the exact ratio). I have used this method since 1975 if I don't want to dump the dif fluid, only want to know what gears are in the housing.
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