[Supras] Help! New vibration MKIII Supra Turbo - at 72mph+ post mechanical work

[Dell Anderson]

A new problem has appeared after my new mechanic 'fixed' my car:


(a $9k repair including intake manifold gasket replacement, new hoses, new
struts, balljoints, 4 new Goodyear Eagle tires, AND a drive shaft rebuild):

Now has a new Vibration that is worst above 72MPH that causes the front
seats to vibrate more than the rear seats (judged subjectively by placing my
hand lightly on the seat behind and comparing it to the driver's seat.

Noisy humming sound reminiscent of that of a slightly muffled ship's engine
room.

Shifting the Automatic overdrive off/on  does NOT affect vibration frequency
(although engine RPM changes between 2500 to 3000RPM+)

The full story:

As some here may or may not recall, I am the lucky original owner of a 1990
Supra Turbo which I plan to keep indefinitely.

After researching repair shops here and elsewhere I found a repair shop here
in Northern California with a ASE certified mechanic that appears to be
top-notch and with whom I quite happy: honest and fairly meticulous, the
rare kind.

"While I was there" they replaced the struts and front ball joints (said one
balljoint was dangerously loose) and bought four new tires because they said
the bad strut and balljoint had caused uneven tire wear and I didn't want to
replace just two.  Also had them check the driveline because a Toyota dealer
had previously told me I needed a new U-joint.  My mechanic had the drive
shaft rebuilt at an outside shop.  I had the mechanic check the compression
and it was fine (No blown head gasket = good, I've already had two in the
past).

When I picked up the car, it now idles fine, but I immediately noticed an
excessive vibration which worsened about 72MPH. This was a new finding. I
immediately called them but I had to meet an appointment so I returned the
Supra the next day.  The shop admitted that the mechanic had not driven it
at freeway speeds after the repair, and was very apologetic for letting it
out of the shop with this vibration.

The mechanic removed the driveshaft and sent it back to the rebuilder.
When it came back, they put it back in, the mechanic drove it again but it
still vibrated so badly they sent it back. This time, the shop owner states
that the driveshaft rebuilder (for $100) 'cut the rubber out' and replaced
it (or something to that effect) and when the driveshaft was replaced, the
mechanic drove it again and said it was "about 80% better".

I spoke with the owner of the shop this afternoon, but the mechanic was not
available.  The owner explained that the mechanic thinks it might be the
rear bearing of the (automatic) transmission which is a little loose (which
would fit with where I noticed that the vibration appears to be coming
from), and that it might require a whole section to be replaced if the
individual part is not available.  Reading between the lines it sounds like
the shop owner thinks my mechanic is too "anal" (his words). Now the shop
owner wants me to drive the Supra to see if it is 'good enough' or at least
back to what it was prior to the repair.

I had never noticed a vibration before, the car was quite smooth before and
I regret letting them mess with the driveline, although I have no reason to
doubt that the rear bearing was indeed bad and that the U-joints needed
replacing.   And I know from experience with a prior old clunker car that
vibrations seldom get better with time and in fact, like an ill-fitting
shoe, become more and more annoying.

Within the last 4 years I have had the tranny rebuilt so I am loath to do
more than it needs unless I have to, but I don't want this vibration.  I
asked him if the driveline rebuild shop they patronize does not warrantee
their work, and he explained that my mechanic was "anal" and they wanted my
opinion before they pursued it further.  I let him know that I am a very
picky customer and unlikely to be satisfied with 80%, as the car did not
vibrate before, in fact it ran smoother at speed than it did at idle (due to
the intake manifold leak causing over-rich fueling).

I did a quick search of my saved Supras.com list postings and found very
little on this subject, but there was a post about U-joint phasing, which I
know from experience with another vehicle that this can happen, but I doubt
that is the case with my mechanic because he is compulsive and a
perfectionist and unlikely to have got that wrong.

Currently, I plan to test drive it but I already warned the shop owner that
I am unlikely to be satisfied with a 20% increase in vibration.

Any advice regarding front drive line vibration appearing after a driveshaft
rebuild is welcome.

Thanks in advance,

Dell

PS - the shop did a nice courtesy detail and had the rear tinting replaced.
Now if I could just stop the mid-front vibration and the rear hatch
squeaks....

PPS Also would like to discuss possible causes of decreased power (catalytic
converter clogged from over rich fueling?) and best possible way to convert
AC to R134 system which DOES NOT LEAK!!!  I'm tired of every spring having
to recharge my system or worse.