This might sound rather daft but here it goes.

I have a 95 deville concours. I was looking to do the 3.11-3.71 final gear swap but with the trans that I managed to grenade at test and tune at my local drag strip at the beginning of the season . I decided it would be easier to just get a trans with the 3.71 already in it.

Now, my question is aside from flashing the pcm to tell it that it no longer has 3.11 gear in it is can I just swap transmissions without any other head aches? Let's say from a sts or something of that nature? I wouldn't think so but I figured I'd better ask anyways.

Thank's

Andy,

 

Anyone?

 

There are a few things that will need to be correct for this to work. One is making sure the PCM can be flashed for the different ratio.
Another thing, if you are just going to swap the entire trans, be SURE it is from the same year model era. The early 4T80Es have different internal wiring than the later ones. There is also the issue of the NSS(neutral safety switch), or MLP(Manual Lever Position) switch. Early units have the MLP on the outside, where the shift cable connects. Later units have the MLP internal. They will NOT swap.
Physically, all 4T8OEs are the same, as far as bolting up. There are minor differences in studded bolt locations, and the side covers are different, but both of these can be swapped.