Need to know gear ratio -
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post #1 of 8 Old 01-10-2010, 01:23 PM Thread Starter
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1987 YJ Wrangler 
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Need to know gear ratio

I got under the Jeep and it has a Dana 30 in the front. I can't make out anything else except stamped numbers reading 43622. I hear that the 4.2L YJ's came with 3.07 ratio. I need to replace the rear end and need to match these up. What should I look for?

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post #2 of 8 Old 01-10-2010, 01:26 PM
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there should be a small plate between 2 of the blots on the dif cober that states your gear ration, if you cannot find it, I would suggest e-mailing "Jeep" (I cannot find the link) and getting a build sheet....that is, if you are sure it has not been modified already.

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post #3 of 8 Old 01-10-2010, 01:26 PM
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If you need to replace the rear end, open up the rear diff and look at the stamp/casting number on the ring gear. That will give you your rigs ratio.

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post #4 of 8 Old 01-10-2010, 01:29 PM
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There might be a steel tag that has the axle specs on it held under one of the cover bolts, or another option would be to pull the cover and count teeth. Other than that i'm afraid i'm not much help...

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post #5 of 8 Old 01-10-2010, 01:37 PM
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last resort, count the teeth, # of ring gear teeth/ #of pinon teeth = gear ratio
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post #6 of 8 Old 01-10-2010, 01:39 PM
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Use this link and provide your full VIN for the build sheet: Contact Jeep
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post #7 of 8 Old 01-10-2010, 02:23 PM
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Jack up the rear end. Count driveshaft revolutions while rotating the tire. Turn the tire 2 complete rotations if your other tire remains stationary and does not rotate. Turn the tire 1 complete rotation if the other tire turns in the same direction. The number of times the driveshaft rotates equals the gear ratio. If the driveshaft rotates about 3x, the gear ratio is 3.07. If it rotates 3 3/4 turns, the gear ratio is 3.73. You can mark the driveshaft to help you count.

tape a string onto the driveshaft if you want to make it fool proof
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post #8 of 8 Old 01-10-2010, 07:28 PM
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x2 on the rotate and open the diff test.

I had an axle with a tag saying 3.07 on the front when I got the jeep and I popped it open and it was 3.07!

I did a spin on the rear and calculated 3.73 but the darn tag said 3.07. Popped the cover and it was an aftermarket pinion gear with 3.73.

Since then, when I buy axles at yards, I ignore all tags and pop covers and read the rings.

The guys are saying read the ring gear. It will not always just say 3.07 3.73 or 4.1 on it. It will say something like "41 10", or 41 ring gear teeth and 10 pinion gear teeth, or 41/10 = 4.10. Or.."41 11"...41/11 = 3.73...etc etc...
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