I have been boring folks over the last few months about my efforts to
solve a prop shaft vibration problem, narrow band 50 - 60 kph approx.
I have recorded the approaches I have taken on my blog

http://shufti.wordpress.com

briefly... I replaced u joints with aftermarket, ones, checked
internal bushings on shaft, fiddled for ages with front diff flange
angle (attempts to match trans flange angle), aligned flanges
laterally and check with laser jig, running with loose diff mounts
etc, etc

all to no avail. Unfortunately there seems to be no local driveshaft
balancing outfit locally so I did not have shaft balanced.

So, as a last resort, a few days ago I tried the "hillbilly" balance
method, ie a gear clamp attached to one end of prop shaft. Initial
position of clamp was randomly chosen and had no effect. With no
confidence in success, I rotated clamp 90 degrees on shaft and tried
again. Well blow me :) it made a big difference. The vibrations are
pretty well gone. Just the slightest perceptible vibes at same speed
range.

I am encouraged by this and will now refine position, and maybe add a
little more weight (penny?) under the gear part of clamp.

Now I will search more thoroughly for drive shaft balance service.

Bottom line is, it seems to me, is that what might work for one
syncro may not for another. I will summarise, with measurements, all
that I have tried on my blog soon.

Of course, in hindsight, balancing shaft after u joint replacement
seems obvious. I would have done that if it could be done locally.
Others have not bothered balancing and had no problems, again
pointing to the multifactor nature of this problem.

cheers

alistair