The Stovebolt Site Forums The Shop Area The HiPo Shop Drive line vibration.

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

It sounds like you have narrowed it down to the converter. Can you try swapping to a different converter? Checking the adapter run out would also eliminate another possibility too. I haven't heard of an unbalanced converter but anything is possible with mechanical parts.

SimS

You may want to check the balance on the flex plate itself in your application since it seems you've eliminated the motor, rear end, and driveshaft.
(I had a driveshaft once that was balanced, but, had a tad too tight a fit into the T400 tail shaft & I ended up with a noisy/failing U-joint. I got lucky on that one and avoided any trans or engine thrust issues!)

Also, in my big block Buick shop manuals (455s) there are service procedures for addressing customer complaints of vibration in the driveline.
After all other causes have been eliminated they suggest placing clip-on weights
directly on the flex plate at various positions until the vibration has been minimized or eliminated.

Perhaps a trans shop could spin up the trans with the flex plate and converter on a trans dyno to do this for you ??

Just a thought

Darn good suggestion there; kind of like taping a penny on each blade of a ceiling fan to find the culprit blade. Thank you.

Are the flages on your propshaft perpendicular to each other's if not this can give you fast slow motion which leads to vibration,,,

It sounds like the converter is the problem, and TH 350 converters are about as plentiful as anything automotive. I'd suggest swapping converters to see if the vibration goes away or changes noticeably.
Jerry

You may have gotten the proverbial "one in a million". I'm with Jerry, change the converter.