Hello and thanks for being here. I have a 12 bolt rear from what I believe is a 70 Camaro. The numbers I have found are as follows.
Axle tube passenger side forward surface: RL W138 2
Casting number: 3969341NF
Casting date: L 290

Here is what I think I know, it's a 70 Camaro 12 bolt dated Dec 29 1970.

I suspect the posi was added to an open rear end? The ring gear has a spacer between the itself and the carrier.

Any info would be greatly appreciated. Not to offend any Camaro guys, but my plan is to put it under my 55 Chevy. I have a 3.08 open stock type rear end now with a 350 TPI and 700R4 tranny. I don't jump on it often, but as it is if I nail it from a rolling start of about 15MPH it spins the right rear tire for 15 or 20 feet before planting itself.

http://pic13.picturetrail.com/VOL463/2783628/5585717/71579839.jpg

Thanks again Mike

The '70 Camaro rear end is about 3 inches too wide for your '55. The '55 rear end should be about 58 inches and the Camaro rear end will be 61 inches. The '70 Camaro 12 bolt is a one year only rear end and pretty rare. Why not put something a little less rare under the '55 and sell the 12 bolt to a second gen Camaro owner? A 9" rear end from a '57 to '64 Ford would fit easily with the bolt pattern redrilled.

Thanks Mr. Byar. But actually both measure exactly 60" axle flange to axle flange. Not that there is anything wrong with a 9", most guys run them, but I kind of like the idea of keeping the 55 all GM if I can.

If the Camaro rear end measures '60 inches then it is a '69 rear end, not a '70. The '70 is 61 inches.

Well I have been reading all I can online. The stamped numbers/letters 'BL W138 2" would appear to be 1971 numbers BL=12 bolt open 3.07 thru 3.73, W=Warren MI plant, 13= 13th day, 8=Aug. and 2=night shift.
However, the casting number "L 290" indicates 1970 and as far as I can tell, the 12 bolt was last used in 1970. If what I read is correct, the 71's had 10 bolt rears only.
The posi carrier appears to be a series 3 "30140PM1"
I double checked the width and from axle flange to axle flange is in fact 60". The spring pads are 42 1/2 center bolt to center bolt.

Your 12 bolt could also be from a '71 Nova. This would explain your date code in '70 and it would apear to be from a Camaro as that year, Nova rear is the same as a 1st gen. Camaro.

http://www.novaresource.org/axle.htm

TJ beat me to it. Looks like a 71 Nova rear, originally 3.07 open. 71 was first year for Julian date (138 would be sometime in May 71, I think).

Same dimensions as a 67-69 Camaro.

Thank you gents! That makes perfect sense. Great site here.

30140 is a 3 series Eaton posi. Are you sure that you want to put it in the '55? Those things are getting hard to find.

Big, the truth of the matter is I would really rather have a posi for the 55-64 original housing in a 3.70 or 3.50 gear. But, I have this rear and all appears to match up for a fit. I guess there is something in being able to say it has a '12 bolt posi' but I'm not given to blowing my own horn.

What if I built you a posi for the '55 and you bring the 12 bolt down to me for a swap? You are only about 2 hours away from me.

I sent you an e-mail. Thanks

I e-mailed you because I didn't read the posting agreement well enough

Oh man,Ive been looking for a 12 bolt around here for a long time. :clonk:
I still have no rear whatsoever for my 69.