Hi Im considering doing a motor/trans swap and I was wondering are the motor and trans' the same from 1997-2004? I looked on ever-unreliable wikipedia and it shows some stuff about gear ratios, but I asked a parts yard and they said to use parts from either Bonneville or Lesabre. This led me to believe that the motor was the same from 1997- but that the trans may be different. I know its a 4t65-e and not to use one from a SC 3800 but what vehicles specifically should I use it from?

This is a gray area. The more you know the easier this is..

Engine: I would suggest 99-04, 97/98 had some changes in casting that shouldn't affect performance, but there were changes Any NA 3800 motor should be fine for you. One or two things would need to be swapped, like a bracket or oil filter adapter, but that is all.

Transmission: There are four overall gear ratios available. 2.86, 2.93, 3.05, and 3.29. 2.93 is the HD transmission, all the other gear ratio'* have drive/driven sprockets with 35/35 teeth, therefore the gearing difference is in the differential. The Diff can be swapped easily if yours is good. (2 bolts). There are differences by year on the transmission that would make swapping easier or tougher. Those should be further researched etc. A nice writeup can be found at Tripleedgeperformance.com

I have the same question, I already broke down the old motor, and the new one is out of a LeSabre. Do you have a picture of the motor mount bracket attached to the motor so I can see how it fits?

I swapped a motor from a Grand Prix that was a front mount and kept my same old side mount in mine. We just swapped mounts. Im just worried about the gear ratios and getting the right transmission and if I do get the wrong one, how hard is it to swap a differential out

Not horrible. To swap a diff you drain fluid, pull the passenger axle and the 3 or so bolts on the cover. Pop the diff off the shaft and reassemble.

Does anyone know offhand the stock gear ratios for an SE and SLE 2000-2005 Bonneville?

2.93 I believe.

They are both the same? If so that would be perfect.

Stock SE/SLE would be 2.86 or 3.05.
Stock SC'd cars all got 2.93

The SE/SLE had drive/driven gears of 35/35 with a differential that gave the gear ratio. Therefore with programming and a diff an SE/SLE could change gear ratio.

The SC cars got 33/37 drive/driven and a 3.29 geared diff. As well the SC trans has an HD diff that is bigger than the SE/SLE diff. Requiring a different diff cover and shorter axle.

Ill try and find an SE then if I cant get an SLE trans then. Apparently it will be too much work to use an SSEi.