340 -727 -3000 stall- Vibration under load - Trying to find source

oldkimmer said

The drive shaft may still be spinning at 60 mph but it is not under any load then. Neither is the differential. See where we’re going with this? Ok try this. Drive it at the same 3000 rpm in first and second and see if u have the same vibe in those gears. Kim

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I did start thinking about load/no load as you mentioned. It does vibrate equally in 1 2 and 3rd gear at the same rev. Also in park and neutral. Which is another reason I was leaning more towards engine in balance or converter. As it does vibrate when it’s not moving.

What about the stall converter being pulled to far forward to meet the flex plate? I haven’t checked that yet. I know many say to shim the flex plate to converter to achieve 3/16-1/8” spacing of the converter to pump from the fully seated position?

the diff is a tiny bit noisy, but was declared fully rebuilt. To me it doesn’t feel like that, but now, perhaps more than before I may be leaning towards driveshaft and rear unjoint that is a tad loose.