1956 rear - is it worth keeping?

[Donald H.]

I have the differential housing that I pulled out of my 1960 when I restore it. I put in a correct posi housing. What I pulled out is casting 3707306, which is for 56 corvette or passenger car. It is stamped (or appears to be) BA1006. I don't see BA listed as a Corvette code so I assume this is from a passenger car.

If so, then I assume there are thousands of these readily available it isn't worth much, so I may just pull the gear set and send the housing to recycling. The ring gear and pinion are 3.70 and look decent so I may pull them and keep.

Any suggestion appreciated.

Thanks,

Don

[Edward M.]

Re: 1956 rear - is it worth keeping?

BA1006 is a passenger car three speed 3.70 rear gear unit, assembled on October 6th. I might suggest just keeping it together if you plan on hanging onto it, you never know when a rear chunk will come in handy. Yes they are fairly common, but the gear ratio is a bit more desirable that some of the others. I sold a 56 3.55 gear assembly in decent shape a few years ago for $25. It cost $55 to get it shipped to Texas, but the buyer was willing to pay it.

[Donald H.]

Re: 1956 rear - is it worth keeping?

BA1006 is a passenger car three speed 3.70 rear gear unit, assembled on October 6th. I might suggest just keeping it together if you plan on hanging onto it, you never know when a rear chunk will come in handy. Yes they are fairly common, but the gear ratio is a bit more desirable that some of the others. I sold a 56 3.55 gear assembly in decent shape a few years ago for $25. It cost $55 to get it shipped to Texas, but the buyer was willing to pay it.

Thanks, I may just box up the whole thing

[Tom P.]

Re: 1956 rear - is it worth keeping?

Some people may, or may not, know that there are signifcant differences between 55-56 and 57-64 rearends. The pass cars first got this style rear in 55 and continued to use it through 64.
First, the 55-6 rear is thinner, lighter, weaker than the 57-64 versions.
Even though the 55-6 center section is a 100% bolt-in interchange with the 57-64 center sections, the GUTS are different!!!! Also, even though ALLLLLL 55-64 ring gears have the same (10)bolt pattern and will PHYSICALLY bolt onto ANY 55-64 ring gear flange, the 55-6 ring gear will not work on a 57-64 differential or vice versa. And, the 55-6 differential will not work with the 57-64 ring gears. There are TWO specific reasons why 55-6 and 57-64 ring gears/differentials are unique to each other: First, the 55-6 ring gears are THINNER than the 57-64 ring gears (translate weaker); Second, the ring gear FLANGES of 55-6 and 57-64 differentials are at DIFFERENT OFFSETS on the differential.
Now, here is what CAN BE DONE. The entire guts of a 55-6 center section can be swapped into a 57-64 case, or, the entire guts of a 57-64 rear can be swapped into a 55-6 case. Furthermore, if a person has a 55-6 rear, and wishes to convert it to a posi, simply installing a posi unit into a 55-6 case and using the 55-6 ring gear WILL NOT work. The reason is because the offset of the ring gear flange of a posi unit is made for the thicker 57-64 style ring gears.
Bottom line: 55-56 ring gears and differentials and 57-64 ring gears and differentials MUST be kept together. As COMPLETE assemblies, they can be swapped into either the 55-6 or 57-64 case, but that's all that can be done. Therefore, if the ring and pinion are pulled out of a 55-6 case, they will only be compatable on another 55-6 differential.

Below is a comparrison between 55-6(left) and 57-64 differentials. As can be seen, the 55-6 is not nearly as massive as the later 57-64 and notice the ring gear flange of the 55-6 does not cover as much of the ring gear.



This is a comparrison of the thickenss between 57-64 and 55-6(right) ring gears. There is not much difference, but enough that they are not compatable with different differentials. Both of those posi units are 4-series.



The two pictures below show the difference in webbing (translate strength) between 55-6(top picture) and 57-64 cases.




I personally would hang onto the 56 rear. Trust me, as soon as you toss it, there will be someone who is desperate for a good, correct dated 56 rear. Even though the letter code is for a pass car, it would still be good for a 56 Vette (MINIMAL point deduct) because it has an OCT 55 date and the very first 56 production Vettes began in Jan 56.

[Joe L.]

Re: 1956 rear - is it worth keeping?

If so, then I assume there are thousands of these readily available it isn't worth much.......

Don

Don-----


There USED TO BE plenty of these around. Nowadays, I think there are a LOT less. Most of the iron this old has been rendered scrap and shipped to the far east.

[Donald H.]

Re: 1956 rear - is it worth keeping?

Thanks Tom and Joe. Tom's pictures do verify that what I have is a 55-56 rear.

I'll box it up and keep it.

[Tom P.]

Re: 1956 rear - is it worth keeping?

If the casting number is 306, then it is for a fact a 56. So far, it SEEMS that the 306 case is 56 only. There seems to be NO verified casting number for a 55 case, plus, 55 cases don't seem to have had a casting date. Therefore, a "plain" case like the 56 306 case would MOST LIKELY be a 55 case.