HELP!!! Differential I.D. Needed

[Tom Spurgeon]

The saga continues...
I purchased what I thought was a posi-track differential, said to be from a four-speed equipped 1962 Corvette with a 3.70 gear ratio. Once I realized I owned the wrong rear end for the car, I purchased a complete rear end assembly. It was described as a 1960 Corvette rear end equipped with a three-speed with a "non-posi" differential unit. And, NO MATTER HOW LONG I STARE.... THEY LOOK THE SAME!!! - - - Can anyone offer assistance in identifying these "critters"???

The link to the photo illustrations is below.

Again, like always...Thank you for your help,
Sincerely,
Tom Spurgeon




Differential Photo Illustrations

[Larry Clain]

Re: non posi!! Differential I.D.

Sorry to have to break the bad news but you got took on the Posi rearend. You can't see the spider gears throught the opening on a Posi. The ring gear carrier is much larger and does not have a big opening for the spider gears. Usually they are machined on the outside and look like a 4" longer extension of the carrier and it is solid on the end next to the two bolts that hold the gears on. One one each side with two bolts each. They will also have bolts going through the carrier that hold it together.

[Joe L.]

Re: non posi!! Differential I.D.

Tom and Larry-----

I agree; neither differential unit is a posi. It's easy to further confirm, too. If the casting number on the cases (not visible in either photo)is 3752899, then that absolutely confirms that it's a non-posi case. A 1957 to early 1961 posi case would carry the casting number 3743833. A later 61 through 62 posi case would be 3789812. The posi cases also usually have a large "P" cast on them, too.

[Mike M.]

Re: non posi!! Differential I.D.

Joe; didn't the early 57 posi cases have a smaller "P" at 2 oclock as opposed to the larger "P"s thru end of c-1 production? mike

[Tom Spurgeon]

Thank You For Your Help! *NM* *NM*

[Joe L.]

Re: non posi!! Differential I.D.

Mike-----

Yes, I believe that they did. Generally, though, 57 to 62 Corvettes with posi had a "thin", elongated "P". Many 1958 to 1964 passenger cars did, too. "Thin P" units were built at the old Chevrolet Detroit Gear and Axle plant on Holbrook Avenue (now American Axle and Mnaufacturing). Other 58-64 passenger cars, but not Corvettes, used a casting with a "thick P" but of the same casting number. These units were built at the old Chevrolet-Buffalo plant on, I believe, DeLavan Avenue in Buffalo, NY. Incidentally, that plant is also now owned by American Axle and Manufacturing.

[John H.]

Re: non posi!! Differential I.D.

The casting date format will also ID the source of the center section; Saginaw-cast center sections (supplied exclusively to Detroit Gear & Axle, which supplied all Corvette rear axles) used a one-digit year code, and Buffalo center sections (passenger car) used a two-digit year code casting date.

Additionally, a Posi unit won't fit in a non-posi center section casting; the center section casting for a Posi was unique to provide clearance for the larger carrier. A Posi center section casting will accommodate either carrier.