C1 Rear End Case Identification

[John F.]

Guys- I have a 3743833 rear end case (big P) on it. Right below the 3743833 I have A120. I know the A indicates that it was mfg in Detroit Gear and Axle plant. What is the 120? is that Jan 20? What determins the year? btw my car is a late june 59 C1.

thanks.

[Bill B.]

Re: C1 Rear End Case Identification

I believe its January 12, 1960 the P stands for Positraction.

[Gary C.]

Re: C1 Rear End Case Identification

John, on the passenger side of the pumpkin opposite to the cast part number there are letters stamped into the case - what are the stamped numbers? Gary....

[Tom P.]

Re: C1 Rear End Case Identification

The CAST A120 is the casting date, Jan 12, 1960.

Over on the other side, there should be a STAMPED code. This stamped code specifies BOTH the gear ratio and the ASSEMBLY date (mo-day only, the year was indicated in the casting date). This stamped code will consist of TWO letters and 2-4 numbers.

[Ted S.]

Re: C1 Rear End Case Identification

Guys- I have a 3743833 rear end case (big P) on it. Right below the 3743833 I have A120. I know the A indicates that it was mfg in Detroit Gear and Axle plant. What is the 120? is that Jan 20? What determins the year? btw my car is a late june 59 C1.

thanks.

John, Is the P a thick P or thin P? The thick P was a passenger car unit. Like others have said it was cast January 20, 1960 by the A120 date code.

[Tom P.]

Re: C1 Rear End Case Identification

The casting date tells you that it is a thin P, which is what was installed in Vettes.
The Detroit Gear and Axle plant rears had a cast date code that ended in ONE number for the year (ie, 0 for 1960) and they had the thin P.
The Buffalo (NY) plant rears had a cast date that ended in TWO numbers for the year (ie, 60 for 1960) and had the thick P.
The Vettes ONLY got detroit rears (thin P), but pass cars could have either a Detroit or Buffalo rear (thin or thick P).

[John F.]

Re: C1 Rear End Case Identification

Guys- attached are a couple pics. Maybe someone can tell me if this is a thin or thick P. I can't find any numbers stamped on the passenger side. I'm thinking this isn't the correct rear end for a June 59 car. Correct me if I'm wrong.... thanks for all your help....great resource for information!

Cheers.

[Tom P.]

Re: C1 Rear End Case Identification

Guys- attached are a couple pics. Maybe someone can tell me if this is a thin or thick P. I can't find any numbers stamped on the passenger side. I'm thinking this isn't the correct rear end for a June 59 car. Correct me if I'm wrong.... thanks for all your help....great resource for information!

Cheers.

Ummmmmmmmmmmmmmm, did you read my reply???????????
If the casting date has one number for the year (ie 0 for 1960), then it was built at the Detroit Gear and Axle plant.
ALLLLLLLLLLLLLLLLLLLLLLL Detroit posi rears got the THIN P!
Corvette rears ONLY CAME from the Detroit plant!

[Mike E.]

Re: C1 Rear End Case Identification

Guys- attached are a couple pics. Maybe someone can tell me if this is a thin or thick P. I can't find any numbers stamped on the passenger side. I'm thinking this isn't the correct rear end for a June 59 car. Correct me if I'm wrong.... thanks for all your help....great resource for information!

Cheers.

That's a thin "P". It can't be the correct one for your car (too late for a 59 car, because it is well into the 60 production year. With no stampings for an assembly date on the opposite side, it could very likely be an over-the-counter replacement bought in 1960 (or even 1970) when the original in your car took a powder.

[John F.]

Re: C1 Rear End Case Identification

Thanks for the reply. very helpful. I'm now on the hunt for a correct case for a late June bday 59 posi car. if anyone has suggestions where to go, I'm all ears. thank you very much.

[Philip M.]

Re: C1 Rear End Case Identification

Tom,
I have a rear end I am trying to ID the ratio. The drivers side has casting codes "3789812" "L201" Thin "P". What does the date code convert to?
The passenger side has a stamped code of "AM112". What does the AM convert to? The numbers mean Nov 62?
Is this coding consistent for a 1962 built late 1961(Nov or Dec?
Thank you

[Joe L.]

Re: C1 Rear End Case Identification

Tom,
I have a rear end I am trying to ID the ratio. The drivers side has casting codes "3789812" "L201" Thin "P". What does the date code convert to?
The passenger side has a stamped code of "AM112". What does the AM convert to? The numbers mean Nov 62?
Is this coding consistent for a 1962 built late 1961(Nov or Dec?
Thank you

Phillip--------

"L201" denotes a date of December 20, 1961. The date is consistent with a 1962 built sometime after that date. However, it's a 1962 passenger car, not a Corvette. The "AM" axle code is a code for a 3.36:1 ratio unit originally installed in a passenger car. Passenger car and Corvette "third members" are functionally interchangeable.

By the way, while a 3.36:1 gearset was originally installed in this carrier, that does not mean that's what's in there now.

[Joe L.]

Re: C1 Rear End Case Identification

The casting date tells you that it is a thin P, which is what was installed in Vettes.
The Detroit Gear and Axle plant rears had a cast date code that ended in ONE number for the year (ie, 0 for 1960) and they had the thin P.
The Buffalo (NY) plant rears had a cast date that ended in TWO numbers for the year (ie, 60 for 1960) and had the thick P.
The Vettes ONLY got detroit rears (thin P), but pass cars could have either a Detroit or Buffalo rear (thin or thick P).

Tom------


One slight clarification here:

Carrier housings machined and assembled at Detroit Gear and Axle were cast at one of the GM foundries in Saginaw, MI. The "thin P" and single digit year code are thus characteristic of Saginaw castings. As far as I know, Detroit Gear and Axle used Saginaw castings exclusively. These were installed in BOTH Corvettes and passenger cars.

Carrier housings machined and assembled at Chevrolet-Buffalo were cast at the Tonawanda foundry. The "thick P" and 2 digit year code are characteristic of these castings. As far as I know, Chevrolet-Buffalo used Tonawanda castings exclusively. These were originally installed in passenger cars only.

[Philip M.]

Re: C1 Rear End Case Identification

Joe,
TY for the information. It is good and bad news. If you know - If I found a housing cover with the correct date casting code for my assemble date and the proper stamped ratio/date code on the passenger, is that interchangeable with what I have or do I have to go deeper into the axle housing to replace the gears?
TY

[Joe L.]

Re: C1 Rear End Case Identification

Joe,
TY for the information. It is good and bad news. If you know - If I found a housing cover with the correct date casting code for my assemble date and the proper stamped ratio/date code on the passenger, is that interchangeable with what I have or do I have to go deeper into the axle housing to replace the gears?
TY

Phillip------


It's not a cover that would need to be changed; it's the entire carrier housing. That would require removing all of the "guts" from the current housing and installing it another housing with the correct stamped code. And what are you going to have after doing all this? Well, you already have the correct housing casting with the correct casting number and "thin P" and you have a correctly dated housing if your car was built within 6 months after December 20, 1961. So, all you're going to have is a carrier housing that has a correct Corvette axle code---that's it. Lots of effort, lots of money and very little gain. Would I do it? Not a chance.