My '72 SS has a very bad vibration at 3000 RPM. I recently installed a new flywheel and clutch and I beleive it started after that. I asked the sales tech if the flywheel or clutch could be unbalanced and he said that it was highly unlikely. He said it was probably the driveshaft, however it only vibrates at 3000 RPM under or over that it is smooth. Any ideas?

To know if it is the flywheel/clutch being poorly machined, try it in nuetral. Does it shake then?

Does it vibrate @ 3k RPM in every gear? If so, it isn't the driveshaft.

Make sure your tranny mounts are good and tight. Check your U-joints for slop while your under there. Smart thing to do with a new clutch

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-Just call me Otis
71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
BEST 60': 1.85 w/street tires.
BEST 1/4: 12.5 with 1.89 sixty foot (street tires)
BEST MPH: 109mph

Picture of me roasting the tires and other guy stuff (http://www.auburnextremeracing.com/drivers/mike/)
Video of me staging (smoke of course) (http://www.auburn.edu/~ledfojw/vids/mike_chevelle_burnout.avi)

Was the flywheel for a 454 ? 454's are externally balanced and the flywheel will have a large counterweight on it.

Yes, it vibrates in every gear. I'm sure it was the correct flywheel, but it didn't have any weights on it. It does not vibrate when the car is in nuetral.