I bet whoever rebuilt it missed getting the pin of the od servo on the od band.   Its a very common mistake.   It kind of slides to the side and if you dont double check the alignment with a scredriver before putting the servo in, it can easily get in behind it.   That is a good place to start looking.

Last edited by Greg B (8/17/2014 6:22 PM)

To get to the overdrive servo, you have to drop the pan and the valve body.   Then you can access the OD servo.   If its a misaligned od band, it can be fixed without dropping the  whole transmission.  But that is still a lot of messy work to get to that.    I would eliminate everything else beforehand. 

You can do an internet search about replacing the OD band and probably find a thread about this problem I am describing. 

I had that issue last week putting the 4R70W  back together. Drop the pan and valve body. Pull the OD servo piston out and look down the bore. You can see the seat for the piston pin on the end of the OD band. Next to the servo piston bore is a 1 inch square hole where you can see the band. I took a long skinny screwdriver and pushed on the seat to tighten the band. I wedged another screwdriver against the band through the 1 inch hole to hold the band in place. I removed the first screwdriver and reinserted the OD servo piston, seated it and installed the snap ring. I then pulled out the second screwdriver. Since the band didn't spring back, I figured I had gotten the piston seated. Since I was still building it up, I was able to confirm it was seated by looking inside the transmission with a light, but of course, you can't do that. Good luck.