Axle is numbers.

[Rockbottom78]

Hey guys. I cab swapped my truck and didn't keep the original vin number... I need to find out my axle ratio in my 78 c10. It's got the 12 bolt and here are a few numbers I found on the gear housing of the axle.
A238
02
GM88
3896839
I understand that the numbers on the pumpkin don't prove what is inside it but I figure it's got to be a start? Let me know if you have any info. Thanks!
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[sweetk30]

i always say good time for a oil change on a rear end and full inspection . then rear the #'s on the ring gear or count the teeth on the ring and pinion .

best way if you ask me .

[Rockbottom78]

Ah ok. I did the old count the axle rotations per wheel rotation. Looks like I have 3.73 gearing. Thanks
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[wilkin250r]

The most definitive way is to pull the diff cover. But the easiest method is the one you've done, just turn the tire and count the rotations.

Multiple spins give more accurate results. Turning your tires once, you might not be exactly sure if you turned your tire exactly one full revolution, it might be 97%, or might be 103%, and thus it might be difficult to tell the difference between 3.55 and 3.73. But do it 4 times, and you can easily tell the difference between 14.2 driveshaft rotations, and 14.9.

[Rockbottom78]

Originally Posted by wilkin250r

The most definitive way is to pull the diff cover. But the easiest method is the one you've done, just turn the tire and count the rotations.

Multiple spins give more accurate results. Turning your tires once, you might not be exactly sure if you turned your tire exactly one full revolution, it might be 97%, or might be 103%, and thus it might be difficult to tell the difference between 3.55 and 3.73. But do it 4 times, and you can easily tell the difference between 14.2 driveshaft rotations, and 14.9.

That makes sense for sure. I'm going to run it again and see what I come up with thanks. i guess I should just rip the diff cover off and check. I did it a couple years ago (should have wrote down the numbers when I was in there). The next time I want to rip the cover off it's to install lower gears and posi. I just need to get my ratio to input the info into my computer for my ls swap... just so the shift points are where they need to be.
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