89 Jag xjs convt v12 engine vibrates

XJ-S
21

IIRC the shop stated “engine still vibrates with tranny pulled back” (out I assume-jrrr)

Usually by 2500 rpm any signs of a missing cylinder ( or even two ) are gone. Lost in the 60 degree V. Smoothed away. For a vibration to appear at middle revs is unusual.

What could possibly create a vibration in a naturally balanced dual inline six at middle RPMs but not at idle? And OP already eliminated all belt driven systems.

Damper or torque converter are pretty much the only contenders I can think of.

22

How do you support a V12 that is not connected to the transmission and its third of three powertrain mounts? If you hand it from a beam across the inner fenders I would expect it to pass vibration into the bodywork and maybe mislead them?

23

Have you looked at motor mounts?