Engine/Drivetrain Vibration Issues

[jondee86]

From what you have said, the only things you changed (in the last
rebuild) that could alter or introduce a torsional resonance in the drive
train, are (a) the CW&P, and (b) the compression ratio.

By changing the diff ratio, you have not only lowered your overall
gearing for better acceleration, but you have increased the amount of
engine braking available. This will cause a change in gear tooth loading
under deceleration.

By raising the compression ratio (and I assume the ratio went up) the
strength of the cylinder compression impulses will have increased.

Resonance problems are difficult to pin down, and the solution is most
likely easier to find by trial and error, than by theorising

So, if the problem is one of "rattling", it would probably be worthwhile
swapping in another back axle assembly, or complete diff head if you
have one in the OEM ratio (4.3:1 ?).

If the problem is one of "vibration", then swapping back to the heavier
flywheel you had before, may be a solution.

Cheers... jondee86

PS: I would still like to know if you have fuel cut on overrun