eng69

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

My442

No 3.90 gears unless aftermarket.

3.91 was the factory ratio.

What is the code on the axle tube on the passenger side?

eng69

Probably is 3.91. I was just rounding off. I'll have to get the codes this weekend and get back to you.

eng69

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?

jensenracing77

On that rear end it should be on the back side of the passenger tube.

monzaz

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
J D

eng69

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.

Zachb92

Maybe a TB? Look at this chart I found last night on this site when trying to figure out what an R2 axle is.

eng69

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.