O type differential value

Old March 29th, 2019, 10:26 AM
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O type differential value

Looking for opinions on what a O type 3.90 posi rear end is worth. Complete from drum to drum and in good working order. I really don't know a lot about these units.All I really know about this one is that it's a 3.90 posi, 12 bolt cover, 10 bolts in the ring gear, and currently in a 69 GM A-body (not a Cutlass though, and not original to this car). Thanks
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Old March 29th, 2019, 11:14 AM
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No 3.90 gears unless aftermarket.

3.91 was the factory ratio.

What is the code on the axle tube on the passenger side?
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Old March 29th, 2019, 02:18 PM
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Probably is 3.91. I was just rounding off. I'll have to get the codes this weekend and get back to you.
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Old March 29th, 2019, 04:36 PM
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I crawled under the car tonight and looked on the front side of the axle tube and didn't find anything. I may just need to clean it better or get a better view. The only numbers I find are 402227 on the center section. Do they mean anything?
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Old March 29th, 2019, 05:09 PM
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On that rear end it should be on the back side of the passenger tube.
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Old March 29th, 2019, 08:08 PM
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should be a 1970 housing with oiled bearing axles You will need to find the axle tube suffix code (2 digit number letter code example : R2 SA TO T3 etc.) on the passenger back of axle tube between the coil spring perch mount and the cast center section and it will probably be stamped upside down .

Jim
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Old March 31st, 2019, 09:47 AM
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Well it's still hard to see, but I think I found it. Assuming it's upside down it looks like 73. However, it could be a T and it could be an 8. Does this make sense? I'm going to assume T3 as I thought it should be a letter and a number.
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Old March 31st, 2019, 09:56 AM
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Maybe a TB? Look at this chart I found last night on this site when trying to figure out what an R2 axle is.
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Old March 31st, 2019, 10:20 AM
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Yes, it could be a TB, but according to that chart it would be a 2.78 ratio. If so, then the guts have been changed as I know it's a 3.91 ratio in it. I had the cover off and looked at the ring/pinion tooth count, and the rpm at which I'm going 60mph all say it's 3.91. I may just have to wait until I get it out of the car and maybe strip the paint off so I can get a better look. Thanks.
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