When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The date appears to be October 6th, 1965 (J 6 5). The 3789812 "P" (Positraction) case casting I believe was used from 62-64 for 62 Corvettes and 62-64 full size Chevy's. I would assume with a 65 casting date that it was sold as a service replacement part and not originally installed in a car as Chevrolet didn't used the removable "pumpkin" after 64 full size production ended. If it was sold as a complete rear there should be a couple letters and 2-4 numbers stamped on the other side of the front of the casting that would identify the ratio. The last three numbers of the casting number for 57-61 cases was "833".
2025 C2 of the Year ('63 and '67) Finalist - Unmodified
Thanks for the info. The story I was told is that the complete rear end (brake drum to drum including pumpkin) came out of a late 50’s/early 60’s Corvette but, as you pointed out, the date code doesn’t jive. Thought maybe I was interpreting the date code wrong.
The date appears to be October 6th, 1965 (J 6 5). The 3789812 "P" (Positraction) case casting I believe was used from 62-64 for 62 Corvettes and 62-64 full size Chevy's. I would assume with a 65 casting date that it was sold as a service replacement part and not originally installed in a car as Chevrolet didn't used the removable "pumpkin" after 64 full size production ended. If it was sold as a complete rear there should be a couple letters and 2-4 numbers stamped on the other side of the front of the casting that would identify the ratio. The last three numbers of the casting number for 57-61 cases was "833".
This is virtually a very accurate answer.
For several years after production of a car model (for the sake of this subject), it was common for GM to continue to make parts available for replacement through the parts dept. Thus, a part dated 10yrs later than the model of car is not uncommon.
On the drop out center section of this style, I have seen casting dates up to 1967. So, if a person had a 1962 Corvette, or a 63 SS409 Impala and had scattered the rearend, they could still buy a complete posi center section from the parts dept, bolt it in and drive away. Also, if just the posi unit was busted, but the case was still good, BOTH 3- and 4 series posi units could be bought for replacement, or, for building up a posi rear.
Also, 56-62 Corvette axle housings are a pure bolt-in swap-----------------sorta.
In 59, factory traction bars were added (radius rods). Thus, a bracket was welded on both sides on the top of the axle tubes, out near the brake backing plate. This was for attachment of the radius rod to the housing. The radius rods were std on ALL 59-62 Corvettes. Then, in 60-62, a rear sway bar was added. But the bare basic 56-62 axle housings are a bolt-on swap.
SOOOOOOOOOO, my question, does that axle housing have the brackets on top for the radius rods? Only 59-62 axle housings will have these brackets welded on, as seen below.
2025 C2 of the Year ('63 and '67) Finalist - Unmodified
Thanks for the additional information DZAuto. Next time I have the car up in the air, I’ll look for additional markings on the rear diff housing. I suspect the pumpkin was swapped out by someone wanting a 4.11 posi. This rearend doesn’t have the tabs for the radius rods/traction bars as used on later cars. I’m very familiar with this set-up as my first Corvette (a ‘62 bought in 1972) was missing the rods. The frame tab on one side was missing altogether, while the driver’s side frame tab top hole was torn out. As a new, 16 year old driver, I discovered too late that pulling hole-shots caused the rear-end to flip-up and rear u-joint to hit fiberglass. Thankfully, the driveshaft never pulled out of the transmission. The solution involved loosening the spring u-bolts and pulling the diff back down. After doing this 3 or 4 times in the driveway or on the side of the road, I no longer felt the need to burn rubber. I’m guessing that ‘62 had seen some time at the drag strip prior to my ownership. That’s what $1250 bought for a Corvette on a high school student budget!
Read Differential decoding
