Recently purchased an '86 Syncro Westy ..that has what I thought was a
typical Syncro driveshaft vibration.  It would get increasingly worse with
speed....making driving over 65 mph uncomfortable. It has a split yoke
aftermarket driveshaft so I thought that was the problem.

But yesterday I pulled out the driveshaft out and it STILL vibrates
strongly ...only now only between 45-65mph instead of
constantly ...increasing with speed ....like it did before.  Now it's
smooth under 40 and over 65 mph.

The vibration doesn't feel like a wheel balance problem, which I've felt
many times..but I'll try a different set of wheels/tires...just to check.

This vibration feels much more like a high frequency harmonic vibration...

The transaxle was rebuilt by German Transaxle about 25K ago.

Need some diagnostic tips here.

What else in the driveline could cause a high frequency vibration ...with
the driveshaft out.

Axles ??  CV joints?  Wheel bearing ???

How to check/test these?

Warren C.