Rear End Casting Numbers and Date Codes
I have been in search for a 56 Oct, Nov, Dec Date Coded Posi rear end which is going on a 57 convertible that was born in Okland CA. Nov of 56. I finally landed the big on I thought, but not so fast, I have toiled over the casting numbers on the unit I purchased which is 3789812 or 3783812 NOT SURE with a date code of K 3 6 and the large P. My question: Is the casting number correct for the 56 or 57 year and is the date code 1956 or possibly 1960? Any information would be of great help. All of my research has ended in a dead end and has confused the heck out of me.
Thanks for the time.
3789812 is a late 1959–61 Corvette and 1962–4 passenger car posi casting number. Although the date code does not seem to match the casting number unless what is listed below is correct as far as 6 designating 1960. K= November 3= 3rd day 6=? although it may be 1960
According to my information all center sections cast after April 1, 1957 have a „P“ for posi traction cast into the carrier adjacent to the casting number.
The early posi unit you are looking for has 8 clutches and the late model one you have should have 10 clutches.
The early 1957–1959 posi design used eight 3/8" –16 right hand screws to attach the two halves together and the 2nd design 1959 (late 1959) and newer used ten 3/8"-24 left hand screws with a special 1/2" washer to connect the two halves.
Also the early posi used a 30 degree ramp angle on the pinion pins and case and the 1959 and newer used a 45 degree angle so the parts do not interchange.
I hope this helps you.
Your information is most helpful. Thanks so much from Afghanistan. I'll pass the information to the person that is restoring the 1957 Chevy Convertible for me while I'm over here. It has the original FI unit in it that is why Im trying hard to ensure that the correct part/casting numbers are installed. My next adventure will be to hunt down a J 56 date code std. radiator.
Thanks again, keep up the excellent work!!!
Could you tell me what the castings number are on the rear end I have L2161 3726898
On my ring gear, the code: 1 GM 3737957 10 37 3 68 appears. On the case, K2260 GM(T2) 3789812 with a stamping: BM1201 what does all this break down to?
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