Did a ton of maintenance items on my 300CD this Saturday. Drained and refilled the trans (and torque conv) and differential along with quite a few other things. I also replace the driveshaft flex discs front and rear, the center support and bearing as they all needed it. Now I have a vibration when taking off hard or after about 60mph. Car was smooth as silk before. Painted the driveshaft halves before removal and put it back in on the paint marks. Today (Sunday), took it back up to work and put it on the rack. Reaching up from underneath I can work the throttle by pushing on the linkage where it comes out the firewall. I rev it up and run it through the gears and can see no vibration at all in the driveshaft, but it I rest my hand on the small crossmember I can feel it somewhat (None on the center support bearing). So I wonder if maybe I missed by a spline (which I was sure I hadn't. Marks still line up, but I take it apart and try it one spline off both ways and vibration changes just a hint but it's still there. I take the flex disc off and change them around (front one to rear, rear one to front) and no difference. I have a 85 and notice that the factory marks do not line up (off about 8 splines) even though the shaft is in the same place it was before disassembly (as per my paint marks). Had to leave it at that as I had plans I had to leave for. Tomorrow I plan on working late to once again rearrange the splines, this time using the factory marks, and see if it makes a difference. I have a suspicion that it's a center support bearing problem (even though it's new) and want to rule out everything else first. I can really feel it through my seat when I get on it from a stop (at about 15-25 is when it vibrates really bad) and at cruise over 60 mph.