C1 rear posi carrier thin or thick P

[Jerry G.]

I have just returned from the NCRS Rocky Mountain Regional , very nice cars, good turnout, a little chilly today. We were talking about rear end identifiers. I have a May 61 car and the discussion was should this have a thick P or a thin P on the case. Were both used on Corvettes or was it just one or the other. We looked at two units and both carried the 812 ending number but one had the thick shorter P and the other the thin P. It seems weird the GM would use the same casting numbers( part) and not use them interchangably. Any experts out there who can decifer the great generals ways. Is it OK to have a thick P in a May 61 Corvette? Jerry

[Mike E.]

Re: C1 rear posi carrier thin or thick P

In a short answer, no.
Two different castings, two different plants--Corvette 3989812 positraction units should have the thin p.

[Mike M.]

Re: C1 rear posi carrier thin or thick P

Only the thin P was used on Corvettes they were cast in Detroit, they had 1 digit for the year, 1=61, 2=62. The thick P was cast in Buffalo and used on passenger cars they had two digits for the year, 61=61, 62=62.
The thin P was used on passenger cars also not only Corvettes.

[Richard T.]

Re: C1 rear posi carrier thin or thick P

Thin P on Corvettes. Rich

[Joe L.]

Re: C1 rear posi carrier thin or thick P

Only the thin P was used on Corvettes they were cast in Detroit, they had 1 digit for the year, 1=61, 2=62. The thick P was cast in Buffalo and used on passenger cars they had two digits for the year, 61=61, 62=62.
The thin P was used on passenger cars also not only Corvettes.

Mike-----


Just a slight change for the sake of historical accuracy. The "thin P" cases were cast in Saginaw, MI and machined/assembled at Chevrolet's Detroit Gear and Axle Plant (by the way, still in operation as American Axle and Manufacturing's flagship plant). These units were used in both passenger cars and Corvettes.

The "thick P" cases were cast at Tonawanda, NY and machined/assembled at Chevrolet-Buffalo New York Gear and Axle (by the way, it was just shut down by American Axle and Manufacturing about a year ago). These units were used in passenger cars.

[Mike M.]

Re: C1 rear posi carrier thin or thick P

Joe thanks for posting that information I love the history of these cars but I also want the story to be accurate.
Thanks again.
Mike