Help with ID of a straight axle posi.

[Dick G.]

Cast 3789812. GM, no X, P, Cast date of K 1 8 or 6. I could not see any code stamping on the right side even after removing the surface rust. The previous owner of my 60 blew up the old posi back before 1974 and a Chevy dealer stuck this one in. Replacement? Corvette or Passenger? Can someone tell me what it's worth in todays market? Thanks DG

[Joe L.]

Re: Help with ID of a straight axle posi.

Cast 3789812. GM, no X, P, Cast date of K 1 8 or 6. I could not see any code stamping on the right side even after removing the surface rust. The previous owner of my 60 blew up the old posi back before 1974 and a Chevy dealer stuck this one in. Replacement? Corvette or Passenger? Can someone tell me what it's worth in todays market? Thanks DG

Dick-----


The GM casting #3789812 casting was used for positraction differential carriers from 1961 through 1964. It was used for both passenger cars and Corvettes. However, all of the units used for Corvettes (and some passenger cars) were cast at Saginaw and machined/assembled at the Detroit Gear and Axle plant. Carriers cast at Saginaw have a "thin P". Other passenger car-only units were cast at Tonawanda, NY and machined/assembled at the Chevrolet-Buffalo Gear and Axle Plant. These units have a "thick P" on the casting.

Functionally, the Saginaw/Detroit carriers are identical to the Tonawanda/Buffalo carriers. I suspect yours started life as a SERVICE carrier and could have been sourced from either plant. The single digit year code implies a Saginaw cast unit, but single digit year codes may also have been used on some Tonawanda cast carriers, too, especially later SERVICE. Most likely the date represents 1966 or 1968 since the carriers were still being produced for SERVICE at that time. It could not be 1958 since the 3789812 was not being produced that early or 1978 since production had ceased by then.