Kent in KC

Casting #'s: 3725899 GM12 I271...Sept. 27, 1961, but the stamped code on the passenger side is AW1002...assembled Oct. 2nd. Can't seem to find the AW code - A is for Detroit Gear(?) but the W is not listed anywhere (W is very clear).

Any opinions?

DZAUTO

If it was assembled Sep 27, 1961, it would have gone into an early production 1962 full size pass car with PG tranny and a 3.08 ratio, NON-posi.

Kent in KC

Thought you'd be the one to answer. Is there a reference source someplace for Chevy passenger car codes?

DZAUTO

BOTH:
My 38-64 Chevrolet Parts book
and
Alan Colvin's CHEVROLET BY THE NUMBERS 60-64
Oh ya, and I just happen to have one on the shelf! I traded a 3.70 posi for a low mileage 3.08 non-posi, which I have already converted to posi with an Eaton posi unit. This gives me a spare for either my 51 Chevy or the 56 Vette.

Alan's books are EXCELLENT additions to any Chevy library.

KimZ

I have a Possi Rear End Differential Chuck # 3725899 GM12 and would like to confirm if this is for a Corvette and if so what year and the Value because I am looking to sell this, any info would be appreciated?

DZAUTO

OOOOOOOOOOOOOOOK, so give us the casting date and STAMPED code.

Now, with that said, ALLLLLLLLLLLLLLLL, and I mean ALLLLLLLLLLLLLLLL 57-62 Vette and pass car (and 63-64 pass car) rearend center (posi) sections, again, I mean ALLLLLLLL, are 100% identical in EVERY way. There is NO difference. What makes one rear a Vette rear and another rear a pass car rear is the STAMPED code on the passenger side of the case. THAT'S IT, THAT'S THE ONLY DIFFERENCE!!!!
Below is just ONE example of the stamped code that I'm referring to.
The TWO letters BEFORE the numbers designate BOTH the gear ratio and whether it is for a Vette or pass car. If it were not for those two letters, there would be NO WAY to tell if it came out of a Vette or pass car.

KimZ

Good afternoon the casting date and STAMPED code is AB928 what does that stand for if you can help me I would appreciate it, or where can you find this info? Thanks

DZAUTO

You have provided the STAMPED code------------------what is the CASTING date (on the other side)?

The AB is from a PASSENGER car with with an automatic transmission (Powerglide of Turboglide).
The 928 is Sept 28, but the year model is unknown because the year is ONLY included in the CASTING date on the other side.

The 3725899 is the casting number for a 57-64 NON-POSI rear.

Depending on what year it is, it will be either a 3.55 or 3.36 ratio. There is no big demand for either in a NON-posi rear from a passenger car. You MAY, repeat, MAY be lucky to get $100 for it.

KimZ

From the photo I only see a CASTING date on the other side that says 61 over the other set of numbers 3725899 GM12.
This one does have a posi chuck.

KimZ

Possibly casting number is 3725898 GM12
each photo looks slightly different when I enlarge them. Thanks

DZAUTO

Will you post 2-3 pictures of the posi unit?

KimZ

Re: posi chuck photos.

DZAUTO

ABSOLUTELY, without question, that is a NON-posi case which has been converted to posi.
It is EXACTLY the same kind of modification that I have done (and have one to do on the workbench right now) MANY times to a NON-posi rear. For sure, the casting date is I 6 1(Sep 6, 1961) and the assembly date is 9 28(Sep 28). So, it all fits.
You definitely have a CONVERTED posi there!
What is the gear ratio?

KimZ

Gear ratio: Gear 41/Pinion 9

KimZ

Any Idea on estimated value for this with a converted posi?
We would love to sell it located in Halifax, MA. Got a Buyer?

DZAUTO

That is a 4.56, which is only good for drag racing or short track racing.
I'm sure there is a buyer out there somewhere, but because of the very low demand, it won't bring much. I would estimate that you would be lucky to get $400 for it. Even though it is a posi for early cars, it is a 4-series posi unit, therefore a 3-series ring gear CANNOT be used on it.
So that posi is limited only to 4.11 through 5.38 gears.

KimZ

Thank you for time in helping me figure out what this is.