I have a multiport fuel injected 4.6L V8 T-Bird. I love this car. The four wheel independent suspension is outstanding. I take the speed bumps my town is infested with at 30MPH. It just glides over them. But alas after about 2 years the transmission started the infamous shuddering. It got steadily worse until all forward motion ceased.. So! I read everything I could find. I talked to dealers etc. End result. I put in a NEW one from the factory. $2,100! Plus!! You are required to put in a new ECM(computer) $350!! I did all this. All service manuals, notices said you must use "ultra high" quality ATF. I used exactly what was recommended $4 bucks a quart.

Within six months it was up to its same old tricks, almost identical.

What happens is a light shudder occurs but ONLY when the vehicle has reached a steady state balance with road conditions and pedal position. It always occurs. It resembles running over a uniform road texture like a very, very, light cattle guard that's hundreds of yards long. No cattle guard noise though of course. Any, and I do mean ANY pedal adjustment stops it instantly. But inevitably the new pedal position will result in a new steady state balance and the shutter returns. For years now I have been driving this thing in a bizarre constant pedal movement mode. As I drive; the instant I feel the shudder come in I make a pedal adjustment to extinguish it. This gives maybe a minute of respite.

Obviously Ford has a problem here as you look at the used car ads you will see that virtually every 4-sale T-bird of this era has a "new transmission"!!! Gag. At any rate what I want to know is what causes this? I have no qualms about taking this tyranny down to it's molecular components, if need be, I have repaired several auto trannys starting in high school. My suspicion is that if I take this thing apart it will not be obvious what is causing it, only perhaps the wear results of the malady.

Since no dealerships appear to repair trannys, they just swap them, I can find no one to tap for info.

My guesses would be:
1) A sensor problem.
2) Software problems that start a shift sees a pressure drop which causes the software to abort the shift which changes the measured pressure which starts the shift... No hysteresis.

Guesses?