Transmission Range Sensor
I had an issue that sounds similar to yours. Not sure but I figure it will help you rule something out or not : )
Sorry in advance about the wordy post:
I have a 2001 Expy with 4.6 engine and 4R70W tranny.
Re: leak at front of tranny. Have you checked the plug on the torque convertor? If fluid id low it could be causing the problem.
My problem turned out to be primarily electronic.
My transmission was bucking real bad when under load (towing a trailer) and seemed to get progressively worse. It was as if it would pop into neutral for moment then back into gear or sometimes it seemed to downshift then pop back into gear..the tachometer would go up to 5000 then back to cruising rpm or it would drop down to 0 then back up to 2500 or so.
Not at any point did it ever feel like it was slipping (that would be typical of worn out clutches or bands) so i felt this was an electronic (computer?) issue and not a mechanical one.
It started to get worse and then do it around town when no towing anything. It started doing this arter, say 60 miles (when warm) then it got to where it would do it just around the block. My first course of action was to drain all trans fluid from the convertor and tranny. Install a new filter, clean all the gunk and metal pieces from the pan, install a drain plug and refill with Mercon V fluid. (105,000 miles by the way) The Mercon is Ford's new spec for tranny fluid that has friction additives, etc..it supersedes the old specs.
There were a few twisted up pieces of metal down in the pan but i figured that I'll just clean and put it together and see what happens. After all times are tough and I'm not ready to drop $3000 on a new trans right now if not absolutely necessary.
My fluid change seemed to help a little bit anyway so it needed to be done but I still had the problem of the trans popping into neutral or 2nd for a moment. After some research I found (on the F150 forum) that the problem could be the "Transmission Range Sensor" (TRS). It's a little electronic device (black) that fits on the driver side of the transmission on the selector level. It tells the computer what gear you are in.
So I decided to change that part. Bought one at a local transmission supply here in Fresno for $36 ! It seems to have fixed the problem! I also noticed on the old one that the connector pins had a bit of corrosion on them which I believe was causing the intermittent problem. It's important to use a spray contact cleaner (available at an electronics supply store) on the wiring harness plug that attaches to the TRS so no corrosion is left over when you install the new one.
This solved my problem, hopefully some of this info is useful to you : )
Good Luck!
