bad vibrations

["Steve Schaeffer" <borrani@domain.elided>]

Hello All,
    Looking for an answer here.  I've changed the stock differential on my
'67 GTV to a limited slip one, a tightened one at that.  Ever since this I
have had a vibration occur from 50-70mph, worst at about 62 mph.  It feels
like a driveshaft out of balance.  However, I didn't touch the driveshaft, I
simply unbolted it from the diff, then bolted it back on to the new lsd.
The car had no vibrations before the change.  I rotated the driveshaft 180
degrees to no avail.  I've had the car up on axle stands and took it up past
70 mph, I felt the vibration come and go while in the air, but my observer
said things looked perfect.  The driveshaft is located to the pinion flange
by a nice raised circular ridge, and appears to be centered beautifully.

When I drive the car on the highway up to 75 mph, then take it out of gear
and glide, it goes thru the vibration period of 50-70mph, so it's not
engine-speed related.  I've tried different sets of tires on the car, no
change.  I did change the trailing arm bushings and the trunion bushings,
but this did not seem to have an affect on the axle location w/respect to
the driveshaft, that angle seems unchanged as well.

If I can't find the answer, I'm going to lock up my old open diff and put it
back in!  Help out-of-tune Turner.

Please advise,

Steve S.
NWARC
Seattle, WA (3 sunny days IN A ROW!!)
http://www.luxline.com/turner

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