Axel identification location... Need help ASAP!

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I need to know my rear end gear ratio and I can't find any identification marks on my axel. I have a 1964 pontiac lemans with a 10 bolt rear end. I have heard on the internet it is on the passenger side. If anyone has a pic to help out it would be much appreciated. I have guessed my rear end is a 3.55 by jacking up the car and counting the tire and driveshaft rotations but I need to know for sure because I am ordering a speedo gear for a transmission swap.

Thank you in advance!
 
How do you know somebody in the long history of this car hasnt already changed the ring and pinion thus making the axle code worthless for your purpose? You have already established you have a 3.55. If you want a more accurate readlng of the actual ratio turn the tire 10 rotations and divide the driveshaft rotations by 10. The location of the 2 character code is described as being on the back passenger side of the axle tube.
 
Thanks Melsg5. I did the 10 revolutions to come up with the 3.55. I was told by a mechanic that that method isn't totally reliable and by doing that method you won't be able to tell between the slight differences in other similar gear ratios.
 
The choices are 3:08, 3:23,3:36, 3:55, 3:90,4:11. By doing the 10 rotation you get a more accurate reading and as I stated even if you find the code somebody may have changed the gears. The 3:55 should be pretty obvious since it's basically 3 1/2 turns of the axle compared to 3 1/4(3:23) or 3 1/3(3:36). If you want to cover yourself get the 3:55 and 3:36 and 3:23. Install the 3:55 and use a GPS with a speed reading to confirm your choice of gear.
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Sounds like you got the info you needed. If you want, you can remove the cover on your rearend. The ring gear will have the ratio stamped on it. Mine has "37/11". 37 divided by 11 =3.36.
 
For some strange reason I feel like I have a GM 10 bolt 8.2 non BOP axle with a BOP cover. I still can't find any markings on the axle itself, unless it's an aftermarket one.
 
I took the cover off and saw there was a Richmond gear 3.55 installed. The part number on the gear shows that it is a 3.55 ratio but it belongs to the non BOP GM 10 bolt family. So if that is the case the cover should be round. My cover is the BOP one with the indents at the 3 and 9 o'clock positions. I will check the website you listed. Thanks again. The only difference I found between the GM and the BOP GM is the spline count.
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