What year Chevrolet differential carriers interchange in a 1956 housing? Are there 2 different carriers; one for high gears and one for low gears (I kinda vaguely remember something like that)? Would a 4:56 necessarily be a Posi carrier? If a person has a 4:56; what are the options for changing to a 3:70 or 3:36 or so?
I'm certainly not an expert, but I think '55-'64 should interchange. I've also heard that some of the posi axles are slightly longer than non posi (or the other way around) but it's not a big deal to shorten. I'm looking for a posi unit for my '57 rear. The factory "P" cases bring in big money for restorers. If you're onlhy looking to enhance performance, Eaton, Richmond etc. make posi units and all the popular gear ratios. I think this is a better way to go as the units are new and often times cheaper than the original "P" cases. Hopefully someone with more knowledge than myself will chime in here.
The difference is in the posi "P" carriers and the non-posi carriers. The gear ratio does not affect this. 55-64 are the years, they are the same and can interchange. If you have a 4.56 ratio, and want lower (numerically), the easiest solution is to find a 3.08, 3.36, 3.55 or 3.70 gearset center section and just swap them out. Finding a posi one is harder and much more expensive. BTW, these rearends are not the strongest either, about like an 8-inch Ford. The 55-64 Chevy has 8.2 inch ring gear. There is a place that does modifications to help them live, but most people just swap them out for stronger in the first place. I have had these rearends under a couple old cars, without any troubles, just do not get crazy with the hp.
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