This is what is great about Lvc.. You get to post issues and get responses from people who may have had the same problem.
This past summer my Tranny was doing the same thing. At about 45 mph I would get the same thing. The sound and feel of going over a rumble strip (what others called a shutter).
First thing I did was tried a tranny flush. I have not heard anything about a car with over 100+ miles having a tranny flush hurt them. In fact that was what was suggested by some very prominent members on this site. The I was also told by other mechanics that Ford created the tranny flush to stop the shutter that could develop. I was told that the shutter was caused by dirt building up on the tranny filter and the flush besides putting in clean fluids also cleaned the filter and put new fluids into the torque converter. It was also suggested that my torque converter could be going. (if you have any questions and want some good advice PM Scott9050,
1wykdmk8, or 94M5 )
there are many others who can offer good advice but I have found these three are usually available (Ray will even sit on the Cell phone while you are working under the car and talk you through the job).
My Thread click here
After the flush the car ran nice for about 2 weeks when the shutter returned, and proceeded to get worse. So it was suggested that it was my torque converter. Replaced my torque converter and problem was fixed.
It's not a real difficult job if you are handy turning a wrench. I has some LvC and local support when I did mine. And if it wasn't for the idiots at Auto Zone I would have had the job done in two afternoons. One to take it out the other to put it back in.
Auto Zone sent the wrong torque converter and claims that there are 2 transmission for a Mark VIII. Don't go to Auto Zone. Plus the gave me the wrong seals for the correct transmission. Even after calling Auto Zone central the idiots there still claimed the Mark VIII had two trannys. After sending me to a guy who knew trannys the guy told me (one of auto zones own) that they were a bunch of dumb $#!+s and I was correct.
So, there is a good chance that you will need to replace your torque converter. Price is about $190 for a rebuilt torque converter. $50 for new Mercon V tranny fluid, and another maybe $10 to $20 bucks for seals if you do the job yourself.
Otherwise you are looking at a near $900 to $1500 job at a tranny place.
