C1 Where/What Did This Rear End Come From?

[Mark P.]

I know, a leading question... I have a 56 with this rear end with these markings on it: H 22 6 3789812 GM6 with the big Positraction P on it.
Tell me if I'm reading this correctly. It is a Positraction rear end (at least the rear axle housing portion) dated August 22, 1956.

I have conflicting information...some stating that there were no positraction units in 56 Corvettes and another reference guide (53-72 Chassis Restoration Guide by Joseph Tripoli Jr.) that states that it is correct for a 56 also...I'm guessing that it meant for the early 57 cars that were produced in late 56. Since the JG does not mention a 56 posi option, I'm inclined to think that this on is an add-on housing portion to an original axle (with no drain in the bottom and only a small vent on the top drivers side).

Still, would this be correct for a '57, even though it was dated August of 56? I guess the 6 months would still apply, right? FYI, there is no stamp (at least nothing is legible) on the passenger side of the housing. Since it won't be judged, I'm not overly concerned, but I would just like to know what I am looking at.

Thanks for your help.

Mark

[Mike E.]

Re: C1 Where/What Did This Rear End Come From?

Mark--
The 3789812 posi unit casting number didn't come in until some time in 1960, as I recall, so it cannot be a 56.
The fact that there is no ratio stamp would reinforce that it was an over the counter unit--probably from 1966. (They were used in production for the passenger cars through 1964). Works well for driving--not too good for judging.

[Mark P.]

Re: C1 Where/What Did This Rear End Come From?

Do you really think that they were producing these old units in 1966? I find that hard to believe. Besides, both Nolan Adams and other resources show that these numbers are good for 1957, That's why I thought if it was an early 57 unit, it would still have a 1956 date code.

[Gary C.]

Re: C1 Where/What Did This Rear End Come From?

Mark, one would have to assume they were still producing those rearends in '66 even though they stopped using them in car production in '64. As Rev. Mike points out that is not a good number for '57. The early '57 positrac Corvettes were "hi torque" and these were EXTREMELY rare and produced in very limited numbers with cast no. 3743833. They also had a small "O" on the right hand side of the snout. In Jan positraction became available and the pumpkin casting was identified with a "X". In March the small P on the 3743833 pumpkin housing was implemented to identify a positrac rearend. Gary....

[Joe L.]

Re: C1 Where/What Did This Rear End Come From?

Do you really think that they were producing these old units in 1966? I find that hard to believe. Besides, both Nolan Adams and other resources show that these numbers are good for 1957, That's why I thought if it was an early 57 unit, it would still have a 1956 date code.

Mark-----


There's no way the GM #3789812 was around in 1956 or 1957. It first appeared later in the 1961 model year.

As far as when this unit ceased being manufactured, it was WAY after 1966. In fact, it may still have been in production in 1976.

[Mark P.]

Re: C1 Where/What Did This Rear End Come From?

Joe,

I stand corrected. The C1's are out of my comfort zone and I definitely have a lot to learn. Could that be why there is no stamp on the passenger side where it normally would be on an original unit?

[Gary C.]

Re: C1 Where/What Did This Rear End Come From?

No stamp normally indicate an over the counter parts sale. Was left intentionally blank for counter sales. Gary....

[Mark P.]

Re: C1 Where/What Did This Rear End Come From?

Thanks Gary, Joe and Mike. You have been a wealth of information. If I went by books alone, there is too much contradiction out there...and people can get side tracked down a wrong path. It's a good thing novices can count on the experts for sound advice. A lot can happen in 50 years during a car's life and it can be a challenge to sleuth through the mystery to find out what really happened to get it where it is today. I guess that's what makes it fun. Thanks again for all your help!

Mark

[Gary C.]

Re: C1 Where/What Did This Rear End Come From?

Mark, please post your 56-7 questions as we have a GRRRREAT 56-7 team that watches this board every day. Additionally there's alot of C1 experienced folks such as Rev Mike. Then there's Joe with all of his vast library of parts books to bail us all out. Gary....

[Mark P.]

Re: C1 Where/What Did This Rear End Come From?

Gary,

I certainly will. I just finished my 66 big block and am anxious to get started on my 56 cascade green project. It is a very late model year car (4399) and has the potential of being a really nice car. The body is coming off in about 3 weeks and the fun will really begin. I'm sure I will have lots of questions moving forward, especially with regard to finish on many items and on which fasteners are correct. It adds to the intrigue because the late cars we subject to several changes from the 56 to the 57 model years.

There isn't a lot of information in the JG or AIM on these cars, so I will be needing some of the details from those in the know. Do you have any recommendations on literature that would be helpful in these areas? I have the C1 Restoration book from Nolan Adams and some other reference information, but I really need more info. Those od black and white pictures are great, but don't always tell the whole story or provide enough detail. I have a local guy with a 57 (fairly early SN...within the first 300 cars), but he's not sure what's correct and what isn't, so that's a bit of a crapshoot. I'd hate to use his car as a guide and find out later that I used it as a model and it isn't correct.

Anyway, I'd very much appreciate any help/advice/guidance you could offer. Thanks again,

Mark

[Gary C.]

Re: C1 Where/What Did This Rear End Come From?

Mark, Noland's book while good is dated. The 56-7 JM is being updated. Best source for your questions is here, the AIM and the JM. When in doubt ask a TDB question. Gary....

[Bob B.]

Re: C1 Where/What Did This Rear End Come From?

Mark,

The 56-57 JG is a little light on the chassis, but there are a lot of similarities with 58-60, so I'd get hold of that guide and particularly note early 58 features.

Bob

[Gilbert S.]

Re: C1 Where/What Did This Rear End Come From?

Mark,

Does you #4399 car have a radio? If so does the wonder bar plain or engraved with wonder bar on it. I have a late 56 #4026 and have lots of pictures on disassembly and reassembly. Actually Gary Chesnut has thel book now. Keep us posted on your restoration of the 56.

Gilbert

[Mark P.]

Re: C1 Where/What Did This Rear End Come From?

It does have a Wonderbar radio and the bar is plain. I guess it could be either at that point from what I have read. That's what makes it interesting. It does not have courtesy lights, park brake alarm, or windshield washers, though. I guess those items will be easy to pass judging, right? FYI, it was an original two top car, but I need to find a convertible frame for it, among several other things. The search is on.

I'd love to see any assembly/reassembly documentation/pictures if you'd be willing to share. I need all the help I can get especially since I bought the car in the worst possible condition for someone that wants to restore it....the condition where someone else started the "restoration" process and disassembled it only to give up. Actually, they gave up, then passed away and another disinterested family member inherited it then sold it. A true basket case. I love it!

I'll keep you updated on the process as I move forward.

Mark

[Gary C.]

Re: C1 Where/What Did This Rear End Come From?

Mark, if you would take a look at the fuse box. There's a stamped 3 digit number somewhere around the left side mounting hole. Appreciate it if you take a close up photo and post it as well as letting me know what the stamped number is. Thanks, Gary....