Engine/Tranny Vibration

[Death to Ford]

I am having some vibration issues with the transmission in my 99 windstar

When I approach 60km/h the vibration starts and at 70km/h the vibration gets worse but if I go faster to 80km/h or above the vibration goes away. Also, when I get to 70km/h with the vibration happening I hit OD OFF, the transmission shifts and the vibration goes away. If I drive around for a while the vibration will come back at about 70km/h with OD OFF. Also when I am driving with the OD ON and the vibration starts I hit OD OFF and nothing happens but most of the time when I do hit OD OFF the problem goes away. What am I looking at here, the torque convertor? or is the 4th gear the problem?

Thank you, DTF

[Death to Ford]

I forgot to mention that the tranny shifts fine and the fluid was changed like 5000 km ago and the fluid is at the proper level.

[12Ounce]

Have you ever checked the powertrain elect harness for chafing against the ac tubing? .. its a long shot, but an important one.

[phil-l]

Possibility of motor/tranny mounts?