[TR] Vibration

[Geo & Kathleen Hahn]

In a TR4 on 165x15 tires I am getting a vibration that comes on about 58 mph
and goes away around 62 mph.  Vibration is most apparent in the steering wheel
and scuttle.  Not a slight vibration but a pretty good shake.  It goes away at
higher speeds and all is really smooth at 75 and beyond.

What I have tried so far (w/o effecting any change)...

Tried a variety of roads driving in 3rd & 4th w & w/o OD
Had the tires re-balanced (1 took a different weight/different spot)
Put on a different set of tires & wheels
Tried the air pressure specified in the manual (I usually use a much higher
pressure)

I suppose the culprit could be the driveshaft (guess that's the biggest
rotating mass aside from the wheels/tires) but I swear this came on during a
long drive and was not associated with any service or change to the
driveline.

I have considered undoing one driveshaft flange and remounting it 180 degrees
off from present orientation.  Have also considered mounting the brake drum
180 degrees from current.  Right now I'd settle for something that changes it,
even for the worse, to get some clue where to go.

Can a driveshaft that has been in service for years suddenly need balancing?

Any suggestions or ideas?  Thanks!

Geo Hahn