[DeTomaso] Oscillating vibration

[Mike Thomas]

I have about 200 miles on my new motor, and am in the debug phase of the
project.  I've had an interesting issue pop up and wanted to post it to see
if there is anything I am not considering as a potential solution.

When I get up to about 75-80 in fifth gear (2500-3000 rpms), I get an
unusual oscillating vibration.  I've certainly felt alignment or wheel
balance vibrations before in other cars, but never of an oscillating nature
that rose and fell at a constant speed/rpm.  I am pretty sure it is chassis
related as hanging in the same rev band in lower gears does not induce it.
I checked the tightness on all 16 half-shaft bolts, and they are snug.
Next, I am going to have the wheels balanced tomorrow.  If that does not
cure it, I am going to have the balance checked on my new half-shafts.
Other than that, I know both rear rotors are slightly out of true, dragging
a bit at one point when I spin the wheel while it's off the ground, so I'm
wondering if the drag on the brakes at that particular speed sets up a
harmonic between the two rear wheels to create the oscillating effect, but
that would suggest the wheels were of a different diameter and rotating
different speeds.  I had the alignment recently done and no changes to the
suspension or bumps hit to knock it out, but I guess that could be something
else to check.

Any thoughts from you guys would be appreciated.
Thanks
Mike Thomas
Panteras Northwest.