[alfa] driveshaft vibration

["Ed & Marsha Prytherch" <mred2u@xxxxxxxxxxxxxx>]

I have had driveshaft vibration problems with my 73 GTV for as long as I
have owned it. The original driveshaft was re-tubed and balanced by a local
truck repair place and I replaced the U-joints and center support and
bearing. It ran smoothly up to about 60 mph, but then started to vibrate and
cause a drumming that felt like the whole car was resonating. The noise just
got worse at higher speeds. I suspected that the balancing was not done
properly. There were no added weights on the new tube.

A couple of weeks ago, I replaced the driveshaft with one from a 74 parts
car. I never drove the 74 but the PO said that it ran smoothly. He has owned
lots of Alfas and I trust him. I replaced the U-joints and the center
support and bearing. There were no tight spots in the U-joints, but they are
not as loose as the ones on the shaft that I removed. I now have a bad
vibration between 20 and 30 mph and another one at around 60, but I can
drive through it and the car is much smoother at 80 mph than it was before.
I have visually checked the U-joints and they look OK. The one thing that
was unusual when I installed the rebuilt shaft was that the bracket that
bolts to the transmission tail bushing did not line up well with the bolt
holes in the underbody. I suspect that the engine and transmission are not
straight in the car and that the rear of the transmission is not lined up
properly. I am considering loosening the engine mounts and shaking the
engine around, then tightening them up again.

Does this sound like a reasonable plan or are there other things that I
should be checking?

Thanks,
Ed Prytherch, Columbia SC
79 spider
73 GTV
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