Transmission Swap
 

Henry Fords idea of identical parts for easier assembly and subsequent replacement seems to be fading with most auto makers.
I am up against the, seems common for 2001-2002 XC70s, transmission problems with clunky shifting due to some ingenious device inside the transmission, which has failed. Now not saving me money, the device is now costing me money. I believe is has to do with disengaging the gears, when at idle.
I understand that the 2004 and up models rectified the problem and that those transmissions are in better shape overall than their predecessor.
So, what would be the issue with a swap from a 2004 car?
I am told that the rear output ratio is different from the 2002. OK.
But what about the computer systems? Will the computer freak out having a 2004 transmission in a 2002 car?
What if I have a 2004 car sitting next to my 2002 and can swap anything over, what would be the stuff I would want to, as well as should, swap?
Should I drop the entire subframe with engine, transmission, rear driveshaft, rear end subframe and all, reinstall in my 2002, and expect to have no new and different problems? I can just see it. Car wont start because of some disagreement in software. That would be my luck after all the work of swapping.
I have more time than money at the moment, so figure no money spent on time in this case.
Thank you for your input.

I am not sure about computer issue. But you could not swap the 04 ECU'S into the other car. They are programmed to the car.

Right, ECU will not fit car, but will transmission and possibly engine from 2004 car plug right into 2002 wiring and communicate correctly with the 2002 controllers?

It should as long as there is not anything major difference in sensors. But if there is you can use the 02 sensors instead of the 04 sensors.

Transmission Swap S80
 

I have a 2000 S80 T6 with major problems, but the automatic transmission is solid. I am hoping to

Remove tranny from my 2000 Volvo S80 T6 6 Cylinder, 2.8 L, DOHC, Twin-Turbo
Place in 2001 S80 (non turbo) 6-Cyl. 2.9L

Should compatibility be okay?