I have a 1996 Cadillac Sedan Deville with the northstar engine and automatic trans That will not shift into overdrive. Any ideas?

Which transmission you have in the car?

all northstars used the 4T80.

well, all the FWD ones anyways.

4T80 It is a front wheel drive.

Are you sure it'* not going in to 4th, or perhaps the torque converter isn't locking.

No, I'm not sure. Al I know is @ 55 MPH it runs @ about 3500 RPM'* or so. It just seems not to be shifting.

Ya, that don't sound like it'* in 4th. I would expect about 2500 or so. All other gears work? I'm not as familiar with the 4t80, but if it'* anything like the 4t65e, the 4th gear input shaft can strip out and that will loose 4th. Dropping the trans pan to change fluid and filter should show if that happened because there will be metal in the pan.

I'll try that. Thanks.