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Old 08-22-2012, 01:33 PM
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how to tell what gear ratio in a 64 chevy 12 bolt

how do tell what gear ratio is in a 64 chevy 12 bolt rearend

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Old 08-22-2012, 02:21 PM
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Must be a truck because the car 12 bolt didn't come out until '65. Remove the cover and count the teeth on the ring gear and the pinion gear. Divide the number on the ring gear by the number on the pinion gear. 41/11=3.73 Probably needs an oil change anyway.
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Old 08-22-2012, 04:20 PM
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Thanks gear head, I tried by getting all the numbers off the rear axle and that didn't work. So I did that and came out with 3.73.
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Old 08-22-2012, 04:22 PM
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Jack up one wheel. Rotate it one revolution and count number of times driveshaft rotates. Multiply times 2 equals your ratio.
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Old 08-22-2012, 04:39 PM
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If this is a truck 12 bolt with 3.73 gears then you also have a 4 series differential. I don't know what you have planned, but that is something that you will need to know if you are going to do a gear swap.
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Old 08-22-2012, 05:02 PM
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Nothing to fancy...just restoring it back to original. Just wantin it to have good highway gears.i pulled a 307 out of it and putting a 283 in it.
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Old 08-22-2012, 06:29 PM
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If you are planning on going to something like a 3.42 or 3.07 gear then you will need a 3 series differential. Those gears won't fit the 4 series that you have now.
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