1957 rear end identification

[Joe M.]

On a 1.23.57 built 57 vette with powerglide, the rear carrier is stamped -
BB717x just below an upside down, stamped 'p' about a 1/4" high.
The cast # is 3707306 and cast date is G96.
The rear is a posi and if I recall it is 3:55 ratio as per wheel to drive shaft rev comparison.

According to my March 1, 1957 P&A catalog '306' is the carrier for 1956 passenger and corvette. '889' is for 1957 passenger and corvette.

Is 717 the assembly date and how is it translated ?
July 17th 1956 or do one of the stamped '7's refer to the year?

Could this be the original rear carrier for this car ?

Thanks for your help,
Joe

[Joseph T.]

Re: 1957 rear end identification

Normally there is a casting date on the drivers side. Is there one..and how does it coordinate with the stamp you mention.The BB417..sounds like the rear end id normally stamped on the passenger side.

I have one stamped BB1119.

[Gary C.]

Re: 1957 rear end identification

'57 Corvette rear end (pumpkin/pig) for Corvettes start with an "A" followed by a second alpha such as AE, AH, AN, AP, AQ, AS, AT and AU. Passenger cars rear ends started with "B"'s. Housing should be cast with "372899" non posi or "3743833" for posi. Earliest posi housing I've seen is a Jan '57 and it has an "X" rather than a "P" cast in it. Believe the "P"'s started in the March time frame. If it's a '56 limited slip (posi) housing, it should have an elogated "O" on the nose of the house rear of the driveshaft flange. Hope this helps. The 53-67 Corvette Specifications Guide available from the NCRS store has this informaiton. Regards, Gary....

[Joe M.]

Re: 1957 rear end identification

The P is stamped above/inboard of the stamped assembly date. I cannot see an elongated 'O' near the flange.
To repeat,there is a stamped X that follows the stamped assembly date and gear code.

So the 3707306 cast # on my carrier is correct for a 1956 vette/ passenger car assembled July 1956 and could not have been original to my January 57 vette? I get the impression the 56 model year used the same cast # whether or not a rear was a posi?

The stamped 'BB' code further identifies the carrier as being from a passenger car rather than a vette. Correct?
Does 'BB' represent a 3:55 posi for a 1956 passenger car?

As the rear is an early posi with both a stamped 'P' and a stamped 'X', can it be assumed this is an original passenger car posi rear or an open rear made into a posi?

So the bottom line is, this rear would be useful to a 56 vette owner, 'BB' aside, and if I wish to make the 57 correct I should begin looking for an appropriate 57 carrier ?

Thanks,
joe

[Joseph T.]

Re: 1957 rear end identification

Is there a casting date on the drivers side?

Is there a stamped ID on the passenger side?

Is there an id tag attached to one of the rear bolts?

See below

Joe Trybulec

[Gary C.]

Re: 1957 rear end identification

There was not a 3:55 gear ratio available for Corvettes in '56 or '57. All I can recall about the early limited slip units was the elongated "O" on the nose of the hosing and that could be suspect with my limited knowledge of '56 Corvette posi's. Maybe some of the Late Great Chevy guys can help you out on ID'ing the housing. Gary....

[Joseph T.]

Re: 1957 rear end identification

Joe

Was your 57 a race car..if so..different combinations of passenger car rear ends and other Shock applications were tried..in order to dial in a car.

Joe

[Joseph T.]

Re: 1957 rear end identification CHEVY!

Joe..this might help!

[Joe M.]

Re: 1957 rear end identification

Joe,
There was no metal tag attached.

The car was a powerglide and someone converted it to a 4spd. I'm returning it to a powerglide. Just taking inventory of what I have to work with and want to be sure not to discard something that may have been original to the car. I purchased the car about 1969 and while the original engine and trans were gone the rest of the car was quite original, molested, but original and working.

The casting date and stamped alpha numeric codes are listed in my original question and are found in the standard locations.

The last chart you posted with the passenger car codes is helpful and shows the BB code matching to the 3:55.

Gary, Noland's book lists the 3:55 with powerglide in 56/57, pp 202,203.

Conclusion : There is no way the July 1956 passenger car rear was original to my Jan 57 car.

Was 1957 the first year two different castings were used specific to open and posi rear gears ?

Can anyone confirm the information listed in the March 1957 Parts and Accessories catalog that the rear carrier cast number used for 1956 passenger cars and corvettes is 3707306 and was used for both posi and open rears ?

Thanks for your responses,
joe

[John H.]

Re: 1957 rear end identification

Joe -

Yes, '57 was the first year for two different diff castings, as '57 was the first year that Posi was available. The 3707306 casting was a '56-only part, for open (non-Posi) diffs only. The 3725899 casting was used from '57-'62 for open diffs, the 3743833 casting was used for Posi diffs from '57 to mid-'61, when it was replaced by the 3789812 casting through '62.