Ok i dont have the number that says it all, i cant find it, ive been scraping down every possible location for it on the axle and its just not there, the axle is in the car, and there are two clamps or something bolted on the tubes that most likely are covering where the number would be.

The numbers i did get off the housing are:

6 890 on the top left side (the first 6 might be an 8), (looking a the housing from the rear). C172 on the bottom right side (date code). And on the front facing side a GM59 in the bottom left.

it looks like this:
http://buickperformance.com/12boltchevy.jpg

but that isn't a picture of mine.

Any help, or links to places where i can decode it would be appreciated. Its non-posi too.

C172 is Mar 17th '72. The other raised numbers are misc foundry markings.
The codes you want are stamped into the forward side of the pasenger axle tube. Very shallow hand stamping, may need to be cleaned down to bare metal to see it.

how far away from the housing are we talking, i already stripped a large area down to bare metal with no luck :/

Mine ends 3 or 4 inches from the housing and is a few inches long. Some are stamped closer to or on top of the tube. You did clean the front side first?

"front side"?

If go under hte car infront of the rear wheel and look at the axle on the passenger side, i believe im looking in the correct spot. I cleaned about a 5in wide by 4inche tall section that covers as much as i can see of hte axle with no luck, its just not there... :(

What was the common gear ratio for a 12-bolt "corporate" gm rear? What are the most likely possibilitys?

Originally posted by Chirp08:
"front side"?

If go under hte car infront of the rear wheel and look at the axle on the passenger side, i believe im looking in the correct spot. I cleaned about a 5in wide by 4inche tall section that covers as much as i can see of hte axle with no luck, its just not there... :(

What was the common gear ratio for a 12-bolt "corporate" gm rear? What are the most likely possibilitys? GM book says 8"-10" inboard of the backing plate but it could be anywhere along the passenger side. Something like KK1025B The standard ratio depends on the original engine, trans, and A/C or not - as well as the year of course.

If you can't find it, then you are not looking in the correct location.

http://www.synthetic-oil.com/images/axlestamp.jpg
http://www.synthetic-oil.com/images/axecode.jpg

if you would like i can take a picture of that area scraped to the bare metal to prove to you its not there ;)

We are just giving you the information, its up to you to use it as you see fit.

I don't need to see any photo. If you cannot find anything then I don't know what more we can do. You will have to remove the cover and count the teeth on the pinion and divide that into the number on teeth on the ring gear to get the ratio (Pinion is what the drive shaft mounts to).

Determining a posi is easier, take off cover and observer the center section, if you see a set of gears, it not a posi.

Would a replacement housing purchased from Chevrolet parts have any stamping on it ? Maybe that would explain the inability to find any numbers.

Yes, a replacement housing only would not carry any stamping. But all built assemblies should have been stamped or how else would they ID it in the system.

It also possible what he has is not a GM product? I could be some remanufactured axle using GM cores? I can't say but anything it possible.

If someone sandblasted the axle tube, that could removed the stamped digits if it was only stamped lightly.

my suggestion is to keep looking. i have found many to be more towards the top of the axle tube. if can be difficult to locate if the tube is pitted or very dirty. as stated earlier the stamps are sometimes very shallow. you may want to use a degreaser on the suspected area also. when wet it may be easier to see. good luck