Last night was the first time in a while that I've actually put the tranny into overdrive. When I did the car started vibrating bad. When I shifted it back into normal drive it went away. I tried it once more and again the same thing. What could be causeing it to vibrate like this in overdrive?

 

Most likely an engine missfire. While it is also possible that you have a TCC shudder it would be best to start at the engine. You can check it by using a Vacuum Gauge. When the problem occurs look at the Gauge, if it all of a sudden starts bouncing around (the needle that is) then you have a missfire. If not then it is TCC. You can also do this with a scanner looking for O2 to fix when problem occurs.

 

What is a TCC? To use a vacum guage doesn't the vehicle have to be in park? It would only start to vibrate when I shifted it from normal drive to overdrive when I noticed it start to vibrate I shifted it back to normal drive and it went away, this is all while driving down the street.

 

The reason a missfire is felt in OD is because the torque converter locks up and eliminates the " fluid dampner " made by the fluid in the Torque converter.

 

What would cause it to missfire? I would beable to detect a missfire just by hooking up a vacum guage with the car running in park?