cliff-1972
Well Known Member
I have a factory P case with a 4.11 gear and posi unit in it.What were they in and what makes them so special?I was told the P case is like the N case for a 9" Ford.
What was the big deal with the P case???
- Thread starter cliff-1972
- Start date
" The positraction option became available after December 1956. There were 3 specific early positraction cases. The first case is known as the "no X" case which was cast in December 1956 and was built in January, 1957 for standard production cars. This case will have a December casting date and no "X" which is present on later posi cases. The second case is known as the "X" case and was cast in the last of january through Febrauary 1957, with build dates in Feb. and March of that year. This case has an "X" cast into the case near the letters"GM" but does not have the letter "P" designation. After April first 1957 all factory posi cases have a "P" (designating positraction) cast into the case adjacent to the casting number; the former "X" designation was now gone. This "P" case was used through the 1964 model year in Passenger car "and through 1962 in Corvette models. There were two different casting numbers used for the posi cases: 3743833 for 57-61 and 3789812 for 62-64 and later years for service replacement and over the counter sales.
Now that that is clear as mud there is more. There were two different versions of the "P" cases, one with a thin "P" which was built in Detroit and was the only one used in the Corvette and also some pass. cars, and one with a thick "P" which was built in Buffalo, Ny and was only used in pass. cars.
The above info is not a big secret and is available to anyone thanks to the research of Alan L. Colvin in his "Chevrolet By The Numbers " series of research publications.
Now that that is clear as mud there is more. There were two different versions of the "P" cases, one with a thin "P" which was built in Detroit and was the only one used in the Corvette and also some pass. cars, and one with a thick "P" which was built in Buffalo, Ny and was only used in pass. cars.
The above info is not a big secret and is available to anyone thanks to the research of Alan L. Colvin in his "Chevrolet By The Numbers " series of research publications.
" The positraction option became available after December 1956. There were 3 specific early positraction cases. The first case is known as the "no X" case which was cast in December 1956 and was built in January, 1957 for standard production cars. This case will have a December casting date and no "X" which is present on later posi cases. The second case is known as the "X" case and was cast in the last of january through Febrauary 1957, with build dates in Feb. and March of that year. This case has an "X" cast into the case near the letters"GM" but does not have the letter "P" designation. After April first 1957 all factory posi cases have a "P" (designating positraction) cast into the case adjacent to the casting number; the former "X" designation was now gone. This "P" case was used through the 1964 model year in Passenger car "and through 1962 in Corvette models. There were two different casting numbers used for the posi cases: 3743833 for 57-61 and 3789812 for 62-64 and later years for service replacement and over the counter sales.
Now that that is clear as mud there is more. There were two different versions of the "P" cases, one with a thin "P" which was built in Detroit and was the only one used in the Corvette and also some pass. cars, and one with a thick "P" which was built in Buffalo, Ny and was only used in pass. cars.
The above info is not a big secret and is available to anyone thanks to the research of Alan L. Colvin in his "Chevrolet By The Numbers " series of research publications.
And with all that said, it was just a way to identify the posi units from the non-posi ones. Some claim there is a different amount of clearance internally.
The "N" is totally different as it was a nodular iron case as compared to a stander cast iron one.
CDNpontiac409guy
Banned
Yes, there's DIFINITELY extra clearance inside for the posi unit.
Here's the style that came in the 1958-64 Canadian built cars. This particular one is a pre-62 casting.
Here's the style that came in the 1958-64 Canadian built cars. This particular one is a pre-62 casting.
cliff-1972
Well Known Member
Man,I knew I came to the right place to ask this question
Thanks guys for the info and history of the P case.I still have this unit,don't know what I'll do with it though?Dad has a 57 210 sports coupe,but he will probably use a 12 bolt in that.
Thanks guys for the info and history of the P case.I still have this unit,don't know what I'll do with it though?Dad has a 57 210 sports coupe,but he will probably use a 12 bolt in that.
