what yould the correct casting dates be on a 61 vette rear built in early april? I have seen different casting numbers such as 3789812, 3748833, 3725899, what do these numbers mean? are these casting numbers the same for each year?also were any letters omited in the build casting numbers? i have a rear that is hand stamped AP412 what does this mean?
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Re: C-1 rears
Lee-----
As far as dates go, you just need a date that is within 6 months prior to your car's build date to be "correct" by NCRS and NCCB standards.
The casting numbers identify the various differential housing castings used. Each was used for a range of years and applications.
3789812 was a housing used for late 1961 through 1962 Corvettes with positraction; it was also used for passenger cars;
3748833 was a housing used for 1957 through early 1961 with positraction; it was also used for passenger cars;
3725899 was a housing used for 1957 through 1962 Corvettes with NON-posi rear ends. It was also used for passenger cars.
The "AP" in the stamping refers to a 4.11:1 axle ratio with positraction originally installed in the case. The "412" refers to April 12 (of the year determined from the casting date).In Appreciation of John Hinckley -
Question for Joe and Lee
Joe is right on the casting numbers. The change to the 3789812 carrier occured during the 1961 model, somewhere about serial number 2500 to 4000 according to the NCRS TIM&JG.
Lee, where did you find the hand stamped "AP412" located? Joe, would you have any idea what the significance of "B294" cast numbers in the carrier above the 3789812 on my early '62 unit? I originally thought they might have had something to do with the date but can't decipher according to the NCRS guide. The manual refers to them as a stamping and says they appear on the front right side of the carrier.Comment
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Re: Question for Joe and Lee
It is stamped on the other side of the housing from the casting numbers (on the large flat area)you probibly cant see it if it is painted heavy.Comment
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Re: C-1 rears
Another question: the posie unit has two desighns one says 57-59 has 8 3/8-16 r.h. screws to connect the two halves togeather and 60-64 has 10 3/8-24 L.h. screws. Mine has 8 3/8-24 Lh screws? (L.h. meaning reverse threads if i understand) can someone clear this up for me.Comment
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Re: Question for Joe and Lee
Clare-----
Are there "screw heads" on either end of the alpha-numeric sequence? If so, I feel pretty confident that it represents a date code. That code would be February 29, 1964. There was a February 29th in 1964----it was a leap year and the day fell on a Saturday. I believe that the foundries often worked Saturday in those years. Also, although the 3789812 casting was obviously not being used on Corvettes in 1964, it was still being used on full size Chevrolet passenger cars and they are interchangeable. 1964 was the last year, though, that this casting was used on a Chevrolet car.In Appreciation of John HinckleyComment
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Re: Question for Joe and Lee
Joe, Yes, there are screw heads alongside the casting. Mike Ernst pointed out to me that this casting represents the date, "B294 is February 29, 1964--from a 64 passenger car," although he says that the rear end was used until '65.
I never checked my rear-end numbers, other than the "P" and the part casting # 3789812. Now I realize that the carrier was replaced with a passenger car carrier. Not a big deal I guess, because it's only three points on the judging field. I couldn't find any visable stamped numbers on the passenger side of the carrier, just two threes stamped on the top side of the pig nose, almost over the top of each other. Do you know if the passenger car carriers got a ratio prefix and dated stamped as did the Corvettes? Mine is a 4:11 ratio.
I wanted to eventually get a low three ratio gear for a backup and I wanted to get it in a posi. I've been told the cheapest way to do this is with a passenger car carrier. Now that I already have a passenger car carrier, if I found a correct carrier for my car, could I swap the 4:11 which has been freshly overhauled, over to the right carrier and set the other up for a 3.08?Comment
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Re: Question for Joe and Lee
Clare; A quick way to identifie a corvette posie rear is look at the P, A corvette P is not as bold as a passenger P, it is the same size but not as bold!Comment
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Re: Question for Joe and Lee
Clare-----
Passenger car carrier housings had codes, too. However, the codes were generally different. Also, I don't know if the passenger car codes were stamped on the carriers or if a tag was used. If the passenger car units were stamped, then an unstamped housing could have been a SERVICE housing
The "pumpkin type" removable (or "drop-out" style) carrier housing was not used in any Chevrolet passenger car after 1964. I think that they were used in light trucks after 64 for a few years, but the truck units are not interchangeable with passenger cars, including Corvette.
You could re-gear an original housing with your current gear-set(or, just buy one that already has the corrrect gear ratio installed) and use the housing that you have for a 3.08 or similar gear set. The housings are, as far as I know, not specific as to gear ratio or gear ratio range.In Appreciation of John HinckleyComment
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Re: Question for Joe and Lee
Lee----
Not exactly. You can distinguish some non-Corvette posi housings from the Corvette units. but you can't necessarily distinguish a passeneger car housing from a Corvette housing. The "thick P" housings were cast at Tonawanda and machined/assembled at the Buffalo Gear and Axle Plant. None of these were used in Corvettes; just other passenger cars.
The "thin P" housings were cast at Saginaw and machined/assembled at Detroit Gear and Axle. These housings were used in BOTH passenger cars and Corvettes. So, the "P" configuration, by itself, does not necessarily distinguish between Corvette and passenger car housings.In Appreciation of John HinckleyComment
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Carriers are not always compatable...
Joe, I found out that you CAN put a 4 series gear into a 3 series carrier but you CANNOT put a 3 series gear into a 4 series carrier. It has to do with the size of the pinion and how it lines up with the ring gear. A 3 series pinion has more teeth and is larger in diameter, so where the pinion meets the ring gear is more to one side, (I think I got that right). Spacers apparently can be used to compensate but it's not a good method.Comment
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Re: Carriers are not always compatable...
Clare-----
What your describing has to do with the positraction case and not the carrier housing. The positraction case is the part that the ring gear bolts to and within which reside the differential ("spider") gears and posi clutches. These pieces are specific as to gear ratio range. However, the carrier housing, the externally visible, "pumpkin" which contains everything, is not ratio-specific.In Appreciation of John HinckleyComment
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Re: Carriers are not always compatable...
Joe, Just to make sure we're on the same page, when I refer to the carrier, I'm referring to the "pig", (in this case, casting #3743833), or differential carrier assembly. I would call the "pumpkin" the center part of the axle housing unit. With everything assembled, I'd call it the third member.
I was told, (and I may have misunderstood) that it is the carrier or "pig" casting that is incompatible going from a 4 series to a 3 series BUT not the other way around.
Looking at a cross section illustration of the third member from the top down with the posi-traction differential installed, I can see how the ring gear could be shimmed to meet a smaller pinion, as from a 3 series to a 4 series, but not the other way around. It also looks like a pinion gear would reside the same way in the pig, no matter the size. However, if the diameter of the pinion were too large, as it would be with a smaller 3 series ratio, then it might not fit the differential carrier casting. If the carrier castings are made to be "universal" for a 3 or 4 series rear end then it wouldn't matter. The posi-differential case would then be the issue. Now I'm really confused.
I like to know how stuff works so I'm going to bring my service manual with pictures to my shop the next time I go, for further explanation.Comment
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Re: Carriers are not always compatable...
Clare------
The part that has the casting number that you referred to on it is the CARRIER or CARRIER HOUSING. The part that the ring gear actually bolts to is called the CASE or DIFFERENTIAL CASE or POSI CASE. The CARRIER or CARRIER HOUSING, in your case the part with 3743833 cast on it, is NOT specific as to axle ratio----"one size fits all". The CASE is specific as to rear gear ratio and there are 2 different CASES for the complete range of ratios-----one case fits ring gears for ratios numerically LOWER than 3.90:1 and the other fits ratios equal to or higher than 3.90:1.In Appreciation of John HinckleyComment
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Re: Carriers are not always compatable...
Thanks Joe. You are right. I asked again today while at the shop and they explained it exactly the same way.Comment
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