i was wondering if the bolt pattern for a 4t45e and a 4t65e-hd are the same. 4t65e-hd is from a 1995 park avenue ultra. 4t45e is from grand am.

I do not believe these are interchangeable.

well i had an understanding that some parts could be switched back and forth between them.

These are 2 completely different transmissions, I don't know what you mean some parts can be switched?

Yeah Max is right the 4t65 series pan is bigger.

I've heard of people using a 4t60-65 differential in a 4t40-45 .
From what I saw a few months ago when I rebuilt my 4t45E, they wont swap without some majorwork done on the 4t45 case.
Best leave that stuff to the pro's, not us Joe's. :grinyes:

just my :2cents: