55-57 Rear End

I'm planning on picking up a tri-five 55-57 Chevy rear end this weekend to transplant in my 54 Chevy...Is there anything I should be looking for...IE casting numbers, condition? How would I be able to decipher what gear ratio? Seller says its complete drum to drum and has the e-brake cable with it...

 

Gear ratio it easy, mark the pinion to the case with a marker or paint pen. Turn the brake drum two complete revolutions and count the number of times the pinion turns. That is your gear ratio. Make sure the other drum is not spinning while you are doing this though.

A large P on the case means it is posi case. If your turn one brake drum, the other should go in the same direction if it is a posi.

 

If you are talking about the entire rear axle, the '55-57 has leaf spring pads, the '58-64 are the same except they have coil spring pockets/mounts. Of the '55-57 rear axles the '57 is the better choice because it has larger, one year only axle bearings, and it has a from-the-factory drain plug on it.

Of the pumpkins, any '55-64 car diff will bolt up. However, the '57 and later diff housings are a smidge stronger than the '55-56 ones, due to thicker internal webbing.

'55-56 diffs are open (non-posi) only, while '57-64's can be either open or posi. If the diff is a factory posi, it's typically denoted by a 'p' on the case.

If you end up with an open (non-posi) diff and want posi, Eaton and at least one other manufacturer make a brand new posi for the '55-64 car rear ends.

You can use the pinion:hub calculation suggested to find the diff ratio, or you can also find and decode some faintly stamped info on the diff (if the original ratio tag is long gone). Go to http://www.348-409.com/differential.html for a listing of the codes, etc.

Scott/Gotta56forme

 

I seem to remember also that 55-6 housings, posi or not, if you put big gears in them - 4:11's or steeper, that you have to notch the housing a bit - 3/8" or so - in order for the cluster to fit.

 

I took the rear end out of my 55 chev wagon springs and all. had the front eye shortened and re-roled by a local spring company and just bolted right in a 53 sedan delivery.

 

Gotta covered the details exactly.

Only other input I could say is that a later model ford explorer rear is the same size and has posi and available with disc brakes. Pulled one out for my 57 for 150 bucks

 

I just put a 56 rear end in my '51. It should be 60" wheel mounting surface to wheel mounting surface. You need to drill new holes in the spring pads to center the wheels in the wheel wells if you are using the stock springs. The holes need to be 1 1/2" forward and 1/2" in from the original holes.