1950s 56-57 hydramatic

[Bronze]

Quick question for the knowledgeable people on the forum: Is it an easy thing to put an -56 tailhouse extension on a 57 transmission and thus use it in a 56 car? If so, any other things to be done while the extension is off, Governor clean-up ?
BR
/Martin

[Lexi]

While I can't answer your question directly, I believe one of my older '56 Caddies had a 1957 Hydramatic case with a 1956 tailstock as well as perhaps a 1956 bell housing. I never did any work there myself, but was done years earlier by a previous owner who probably got fed up with transmission problems of his '56. I don't recall any other changes or issues. I believe the transmission case wasn't even Cadillac, (perhaps Oldsmobile), but was a hydramatic. That set up permitted the use of the original driveshaft-as I recall. So this would seem to be in the "definite maybe" category. Clay/Lexi

[dn010]

According to the interchange book, for 1956 an Olds 56 "o" bolts up, extension is different and you need to modify the driveshaft. It does not say that the 1957 can be made to fit like it does for 58, so I'd assume there is some sort of difference that makes so it doesn't work out that easily.

[Lexi]

According to the interchange book, for 1956 an Olds 56 "o" bolts up, extension is different and you need to modify the driveshaft. It does not say that the 1957 can be made to fit like it does for 58, so I'd assume there is some sort of difference that makes so it doesn't work out that easily.

Interesting, as I thought the worn spec plate did say "O", which I assumed was Oldsmobile. I thought the drive shaft was stock, but can't say for sure. Clay/Lexi

[Roger Zimmermann]

The extension is easy to interchange, but you also need to switch the output shaft. It's more or less a major job. You could just switch the output shaft with the reverse drive flange but how will you check if the selective thrust washer is the right one?

[Bronze]

Roger, Do i understand it right: With the extension housing off and having removed the governor housing with the governor, I could remove 2 snap rings and then pull out the output shaft with the reverse drive flange and selective thrust washer ?

But you then point out that i will not know if it is the right selective thrust washer. Pardon my ignorance but i don't know right from wrong...in this case If i pull the 56 shaft with reverse drive flange and selective thrust washer and put the assembly in the 57 trans, can i not assume that the selective thrust washer will be correct?

[Bronze]

Ahh, i get it, the thrust washer is like a shim that is specific to each unit to take up any play...right?

[dn010]

Ahh, i get it, the thrust washer is like a shim that is specific to each unit to take up any play...right?

This is correct.

[Bronze]

And Roger already answered the first question back in 2021. Thanks Roger !

I went to my shop this afternoon. To exchange the drive shaft, the whole internals must go out because the reverse drive flange diameter is larger that the rear case diameter...