I have a 70 Z28 with a 12 bolt rear end with the following codes on the passenger side axle tube:

COO 0311 G 2
E
Note that the "E" below the other #s.

The car's build sheet shows the 4.10 ratio posi rear end. The car was assembled first week of April.

This format does not agree with the example shown on this site for 1970 decoding:
1970 Axle code example: COZ 01 01 G E
(COZ = Ratio, 01 = Month, 01 = Day of month, G = Plant, E = positraction source).

Has anyone ever seen this before?

Your numbers look essentially correct.

COO is a 4:10
03 is March
11 is March ll
G is assembly plant Detroit gear and axle
2 I don't know, but I see it sometimes on axles.
E is Eaton positraction. This number often was stamped on a separate line.

The 2 means it was built on the second shift.
Dennis

BINGO !!!!!! I agree with Dennis

I have a COO 123 G1 E,casting is 3969341NF A60 casting date. Ring gear dated 5/69 and pinion dated 12/69. If the COZ 373 12 bolt was standard,then the COO 410 was optional? How many L78's and Z/28 70 Camaros came with the COO 410 4series 12 bolt rear?? Dan

No statistics on how many of this or that came with what ratio............

Any comments or opinions on what minimun amount I could expect on EBAY for 1970 12 Bolt 3:31 posi, 3:55 Posi, and 4:10 posi dated from march and June ????

The guy I bought the rear from still has the 70 Z/28 4spd car the COO rear came out of.He put a Moser rear in it since he was dragracing it. Car is still all original sheetmetal except for the hood.Still has the original dash with the original guages and Z/28 tach.Still a 4spd. Still has cowel tag,28 10 on it.

High dollar piece.

My 70 Z-28 12-bolt is coded:

COZ0414G1
E

Same format as yours...I just had it blasted down to bare steel and there are no signs of restamping or modification...so yours is not the only one out there in this format.

I think that is a fairly standard format....here is a picture of a spare '69 12 bolt I had:

http://www.members.cox.net/flowjo68/images/BV4.jpg

I have a BU coded '69 as well and it is laid out the same.

All of the '70 12 bolts I've seen have the same lay out...

Shows BV not BU, BV in 68/69 was 410....

Shows BV not BU, BV in 68/69 was 410....
You're correct - my bad...I don't have pictures of the extra BU on the computer but did of the BV just mixed them up when I wrote - sorry