Re: 1955-56 manual overdrive transmission

Posted by HH56 On 2015/12/4 16:05:05

RSG, The complete units are interchangeable however there are some internal differences. The cast iron case was 55 and aluminum case was 56. There were some valving changes and some refinements in 56 units which increased reliability and changed the shift pattern somewhat from that of the 55. A significant change was the spines on input shaft are different so you will need the complete assy including the torque converter. Torque converters will not interchange between years without internal parts swaps. Depending on which model your new trans came out of there may also be some changes needed if your car has a different axle ratio. The speedometer drive gear is one item that may need to be swapped from your old unit. The senior cars have a larger output flange connecting to the driveshaft so that is another thing that could be different. If the new trans came from a push button equipped car it will be missing the lever for the shift linkage which will have to transfer over. Speaking of shift linkage, early 55 cars had a slightly different geometry on the lever and rod length was different. If your car is one of those then you may have to move the lever over even if the new one has a lever.

As a point of information 56 transmissions which were installed in hardtops had a different torque converter which was geared toward slightly increased performance than those used in sedans but they will still interchange.