Rear Center section ID help

[Patrick H.]

Re: Rear Center section ID - some thoughts.

OK,

Still for real, some notations:

1. I'd suspect that the date code is actually A 31 1, for January 31, 1961.
2. The casting 3789812 matches a late 1961 to 1962 positraction differential as used in Corvettes and passenger cars.
3. Since it is an "F_" code, it is a 3.70, 4.11 or 4.56 ratio. F codes only matched with the 4 series carrier, no matter what the year.

So, it is one of the above mentioned ratios, and with a non-Corvette code was likely installed in a late 1961 passenger car.
In 1961, Corvettes used F J/K/L/M for its codes with metallic brakes, but since it doesn't match even that then we know it's not Corvette.

You probably figured this out already, but I still don't see FP anywhere. Maybe someone like Joe L has an old book with FP in it.

Regards,

Patrick

[Patrick H.]

Re: Rear Center section ID - some thoughts.

OK,

Still for real, some notations:

1. I'd suspect that the date code is actually A 31 1, for January 31, 1961.
2. The casting 3789812 matches a late 1961 to 1962 positraction differential as used in Corvettes and passenger cars.
3. Since it is an "F_" code, it is a 3.70, 4.11 or 4.56 ratio. F codes only matched with the 4 series carrier, no matter what the year.

So, it is one of the above mentioned ratios, and with a non-Corvette code was likely installed in a late 1961 passenger car.
In 1961, Corvettes used F J/K/L/M for its codes with metallic brakes, but since it doesn't match even that then we know it's not Corvette.

You probably figured this out already, but I still don't see FP anywhere. Maybe someone like Joe L has an old book with FP in it.

Regards,

Patrick

[Patrick H.]

Addendum

I'm even going to go so far as to say that if the code really is FP (and not FB or another letter) that it's probably a 4.56 rear end.

Why? They use F_ in order. FP is farther in the alphabet than the majority of codes used in the 1961 period, and so I'm going to guess that FP would be 4.56.

I would think it would be moderately easy to check the rear end ratio since we've narrowed it down to one of 3 ratios based on the carrier, by rotating a tire when the rear axle is off the ground, and seeing if you get 3 3/4 turns of the differential to one turn of the tire (for a 3.70) just over 4 (for a 4.11) or 4 1/2 (for a 4.56).

In addition, I could easily imagine someone 40 years ago swapping from what might have been their 3.70 ratio in their 62 Corvette to the 4.56 ratio out of their friend's 61 Chevy.

Hope that helps.

Patrick

[Patrick H.]

Addendum

I'm even going to go so far as to say that if the code really is FP (and not FB or another letter) that it's probably a 4.56 rear end.

Why? They use F_ in order. FP is farther in the alphabet than the majority of codes used in the 1961 period, and so I'm going to guess that FP would be 4.56.

I would think it would be moderately easy to check the rear end ratio since we've narrowed it down to one of 3 ratios based on the carrier, by rotating a tire when the rear axle is off the ground, and seeing if you get 3 3/4 turns of the differential to one turn of the tire (for a 3.70) just over 4 (for a 4.11) or 4 1/2 (for a 4.56).

In addition, I could easily imagine someone 40 years ago swapping from what might have been their 3.70 ratio in their 62 Corvette to the 4.56 ratio out of their friend's 61 Chevy.

Hope that helps.

Patrick

[Clem Z.]

Re: Addendum

my list says FP 3.73 posi,1965-66-67 chevyII,camaro,3.70 1968 chevelle

[Clem Z.]

Re: Addendum

my list says FP 3.73 posi,1965-66-67 chevyII,camaro,3.70 1968 chevelle

[Patrick H.]

Re: Addendum

I found that too (see above), but that doesn't explain the 61-62 differential casting number and date.

Patrick

[Patrick H.]

Re: Addendum

I found that too (see above), but that doesn't explain the 61-62 differential casting number and date.

Patrick

[Dave S.]

Re: Addendum

Thanks guys for trying. Like you I'm confused by the conflicting data. This pumpkin is in a very low mileage car that has seen lots of 1/4 miles so I would suspect it to be 4:11 or 4:56. I seems certain to me that it is not original to a mid production 62 car. The small tag on the pumpkin bolt is missing showing me that the pumpkin has been changed at some point. I'll try to re-check the numbers but I'm pretty sure I am right.

[Dave S.]

Re: Addendum

Thanks guys for trying. Like you I'm confused by the conflicting data. This pumpkin is in a very low mileage car that has seen lots of 1/4 miles so I would suspect it to be 4:11 or 4:56. I seems certain to me that it is not original to a mid production 62 car. The small tag on the pumpkin bolt is missing showing me that the pumpkin has been changed at some point. I'll try to re-check the numbers but I'm pretty sure I am right.