Some help w/ '57 rear axle code

[Garry E.]

I have question regarding the casting number and date code on the rear axle of my '57...... I finally removed enough grease/dirt from the unit to read the numbers.....

This is what I have..... Casting# - 3789812; Date Code - K 1 6..... Over the top of the GM casting mark is what appears to be a "6" cast into the surface.....

There is also a small drilled "hole" in the top of the left axle shaft carrier.... is this some type of vent? I thought only POSI TRAC rear ends had such vents....?

I wonder if I have a "56" rear end in this car..... It would seem a bit strange since the car was assembled on April 4, '57.... Wouldn't this be a bit late to have '56 parts on the car....?

Any thoughts on this......?

Garry Eastwood
#38705

[Mike M.]

Re: Some help w/ '57 rear axle code

differential casting #'s were 3725899 for non-posi and 3743833 for the posi's. i suspect your casting # 812 is out of a pass car. the date of nov 56 would be very unusual for an april 57 vette. there is a hole in the top left of the axle housing regardless of posi or non-posi. if posi, a brass 90 degree elbo threads into the hole with an attached pice of steel tubing. if it was a non posi, the hole accepted a small breather assembly which is common to the pass cars of the 50's . mike

[Eric V.]

Re: Some help w/ '57 rear axle code

Garry,
According to Alan Colvin's book Chevrolet By The Numbers covering model years 1960-1964, the 3789812 casting number housing is for late '61 and all '62 Corvettes with posi, and was also used in '62-'64 passenger cars with posi. I know on the face of it this does not jibe with your date code of K 1 6, but perhaps the housing is a service part purchased in 1966 or 1967. Anyway, it is not a '56 or '57 differential housing. Hope this helps.
Eric

[Garry E.]

Re: Some help w/ '57 rear axle code

Eric/Mike:

Thanks for your comments...... It really doesn't surprise me since the car seems to be a composite of a lot of different parts from various years..... The correct rear axle cover (and the internals....) simply become another part to add to my "shopping list".....

thanks....

Garry Eastwood