So I've hit a wall with my build. I thought I had a possible 57-64 9.3 Pontiac/Olds rear end under my Thunderbird, but now I'm not so sure. I found what looks like a production date code on the 3rd member, but I'm having hell finding a way to decipher it. The code on the side is J316. From what I've been able to find online, the last number designates that the 3rd member was made in 1956. I want to say that the J is a factory designation for October, but I could be completely wrong. If the information I found is correct, this means my differential was made on October 31, 1956. This tells me absolutely nothing because I have no idea when GM started producing the 1957 Oldsmobile line. All I know is that my rear end was made in 1956... Could any of you help shine a light so that I might climb out of the darkness?
Yea, the 55-56 Pontiac rear ends were visually similar to their bigger 57 and later brothers, just to a smaller scale. As noted, a picture or two would be a big help. Mike
I'm pretty sure the 56 Buick still had a torque tube. If the new models came out in Sept they would have started assembly in late July early August, component would have started a month or so earlier.
I tried to post a picture of the production number, but my phone was acting up at that point. I was thinking the same thing. Everything on this car is like this. The car itself is a late 1954 first production run of the 1955 Thunderbird model. The car came with a 1964 1/2 Mustang Toploader with the 25 spline output shaft. If this rear end is an early 1957 9.3 rear end, it falls in line with the rest of this car. I've never seen a 9.3 rear end that was this early.
Like said above...GM normally started production in about September. Your rearend is Oct 31, 1956. By the time that 3rd member was put into a rearend, then into a car, GM had been building 1957 model cars for probably 2 months. Every 1957 Oldsmobile and Pontiac made had that rearend. So your 3rd member is early in the grand scheme of things....but its not thaaat early.
I agree with most of this, but I don't agree with your last statement. As it just so happens, it dates as October (J). If it had been a H (August), this would be an entirely different rear end. We are talking about one month. To me, this is as early as it gets.
Most manufacturer's retool in June or July for the next model year. They start building components before that so when vehicle production starts in usually August they have sub assembly's ready to build cars with.
Scotchbuzzard....yes...what is said above. GM normally stopped building cars in June or so of that model year. My dad worked for GM and I remember as a kid he was always off for the summer, like July and August. He called that time that they were changing the plant as model changeover. I dont know if the foundries cast 12 months out of the year...but I doubt it. They might have been off summer months too. So if they were casting third members in August...they would have been for the following model year. By definition if they stopped building 1956 GM cars in June or so...the casting of the 3rd members must have been before that, probably by a couple weeks.
That rear axle looks to similar to the OEM in my 46 Olds. Check the axles flange for the 9.3" bolt pattern. If you pull an axle and count the splines that may assist, 29 spline up until '58 and 31 spline from 1959 upwards due to larger displacement engines. https://www.jalopyjournal.com/forum/threads/pontiac-olds-rearend-tech-post-it-here.129676/page-2
The early olds pontiac are 10 spline for Pontiac and 16 for Olds. But that center section uses bolts, not studs like whats pictured to attatch to housing.
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