I've run into a problem trying to ID the differential on my '68. It's a 12 bolt diff and my source indicates that these weren't used on the Tempest line until 1970. The main problem is that I've scraped and cleaned and looked 'til I'm blue in the face and can't find the two letter code on the rear of the left axle housing near the pumpkin.
Are there any 1970 axle housings that have NO stamped code? I noticed a few in my reference book that showed N/A where the code should be.

I've run into a problem trying to ID the differential on my '68. It's a 12 bolt diff and my source indicates that these weren't used on the Tempest line until 1970. The main problem is that I've scraped and cleaned and looked 'til I'm blue in the face and can't find the two letter code on the rear of the left axle housing near the pumpkin.
Are there any 1970 axle housings that have NO stamped code? I noticed a few in my reference book that showed N/A where the code should be.

If I recall right the two number is stamped on the right tube at front?

Maybe you're right. I was up pretty late last night looking for it. I might have read it wrong. http://forums.performanceyears.com/g...icon_smile.gif
How about the 12 bolt rear? Can anyone verify that this was only on the '70 models and not earlier?
In the meanwhile, I did find that there were quite a few axles from '68 to '70 with no code.
See here- http://www.teufert.net/pontiac/rears.htm

Greg, is it a Chevrolet-style rearend or an Olds-style rearend? TommyHg is correct on the stamped code location for a Chevrolet-style 12 bolt. To figure out if it was originally a Chevy rearend look under the car, passenger-side, at the rearends' lower corner center section. If it has the casting date in the webbing, it was from a Chevy which were put into Chevrolets starting in '65. Another indicator of a swap, is to see if a conversion U-joint is used at the rear. Most Chevy rears used a smaller u-joint than the ones installed in Pontiacs.

I can't be sure what it is. It's definitely different than the 12 bolt re in my '69 el Camino.
According to the GTO Restoration guide, there should be two letters, not numbers, on the rear of the left axle housing. You can see where I've been scraping paint.
Here's a photo-

To update, I found some raised letters cast into the front side of the diff.
It has the number "16" at about the 10 o'clock position and then at about 8'clock, the numbers "40227". Right at the bottom, ie. 6'oclock, it has the letters "CFD" followed by either an "A" or a delta shaped figure.
Any ideas?

I think it depends on who did the stamping. My 70 GTO has only one partial letter. Must have been a monday morning stamping.

My 1970 GTO 12 bolt does indeed have the stamping "WT" on the front portion of the passenger side axle tube. The original 3.07 one legger isn't what resides inside of the housing now, but no one has to know http://forums.performanceyears.com/g.../icon_wink.gif

Here is what I have as far as stamping goes...
http://forums.performanceyears.com/g...a&ul=557108137

To further clarify, Pontiac A (and G) bodies did not get the 12-bolt rear until 1970, and then only for 455 engined cars.

I've about determined that the only way I'm going to find out the ratio is to roll the car and count the driveshaft revs.