This is not on an old truck but could be helpful on anything with an inline engine using a transmission adapter. My 37 Buick has a straight eight engine with a Bendtsen's adapter to accept the Turbo 350 automatic transmission. It has had a vibration from the get-go. The drive shaft is perfect, checked three times on a Bear strobe balancer---the last time by myself. With the torque converter slid back out of the crank the engine has zero vibration. Moving the converter to the three different positions made the vibration happen at a different rpm for each position. The three bolts/washers/nuts bolting the converter to the flex plate were mismatched so used three of identical weight. Both front pump and rear output shaft bushings are new. This just about leaves only the converter since the vibration happens even with the trans in park. Has anyone experienced or heard of an unbalanced converter? I did not use a dial indicator mounted to the crank flange to check any run out on the adapter. It looked Blanchard ground and NC machined but that is still no excuse for taking a short cut. When the converter is slid back it slides back forward directly into the crank pilot hole and all the way up against the flex plate. I would like to take it on a 3000 mile trip soon and am concerned about a vibration that is transferred directly onto the crankshaft for that long.
Please brainstorm and offer suggestions. Thank you;
Evan

Evan