Reinstalled motor and trany this weekend in my 63 390 and jetaway after overhauling both. Problem: the torque convertor is about 3/16" away from making contact with the flex plate. When I try to tighten up the flex plate nuts the flex plate flexes or bends.   questions: should the torque convertor have some movement to make contact with the flex plate or is it solid no movement? And does the nose of the torque convertor go into the back of the crank shaft?  I'm thinking the back of my crank is rusty since its not the crank that camo out of the car, stopping the convertor from moving forward.

Thanks for the feed back.


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Are they the engine and trany that were in the car before or was something changed ?

Stay safe 

Are you implying you changed the engines original crankshaft ?

The 1964 Turbo Hydramatic flexplate has a 3" opening. The raised back end of the 1963 390 Hydramatic crankshaft and 1964 429 Hydramatic crankshaft is 3 3/16". The flex plate is not going to fit the Hydramatic crank unless it is enlarged to exactly 3 3/16" and it has to be exactly centered!  It sounds like you are trying to mate a 1964 429 Turbo Hydramatic to a 1963 390 which came with the Hydramatic crank. For more details on this and other issues you will run into check out this help page: Engine and Transmission Facts - differences from 62 to 63 to 64 to 65

Be sure to scan down to the Swapping Transmissions - Things to Consider section.

All 390’s in 63 had  the hydromatic trans 

In 64 the 429 —had two trans  mounted to the engine depending on the model Cadillac in 64 

Two  different crankshafts  size ends —-came in the 429  engine in 64 

One size crank —was for the hydro trans 

A second size crankshaft  in the 429 —came in the engines that got the turbo (400) hydro trans which has a spacer in 64 year only 

The correct engine  must be used  with the correct trans depending on the engines crankshaft   End size and —they are not interchangeable due to the size of the crankshaft end that couples to the trans being different 

This will cause a major complication  in matching the correct engine to the correct trans if not done correctly 

As noted in the above post by Jason then a good number of other issues will have to be addressed 

Dropping a 429 with a hydro trans —that came that way in a given 64 model - would work in any Cadillac in 63 or 64 that originally came with the hydro trans making that swap correct and very much less complicated to get done correctly 

Having  two different crankshaft sizes in the same engine in a given year is completely unique to the 64 429 engine very much complicating a trans swap if not understood clearly 

Stay safe 

Thank you all for the comments. I had to change the engine due to a cracked block. I got an complete 63 390 short block, (thank you Russ). completely rebuilt it, but I failed to clean the rust out of the back of the crank where the nose of the converter slides in. I gave the flywheel a couple love taps with a brass hammer and it moved forward just enough. The convertor must move freely in the back of the crank for ballooning.   


Glad it was an easy fix. It was ironic the # you used 3/16" which is the exact different in diameter of the 1963 drive plate and 1964 flexplate.

Glad it turned out to be a simple issue that you worked thru 

Always the best case scenario 

Enjoy having your car back in action 

Stay Safe 



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