'80 vanagon suspension shake

[Gypsie]

I am having an intermittent issue in the vanagon.

While driving it has a symptom that feels like driving over little bumps in the road. (thunka thunka thunka).

It increases with speed and is unrelated to engine speed or transmission of power from the engine to the wheels (as evidenced by putting it in neutral at speed. The thunka thunka is consistent whether in neutral, accel, or decel though it slows as the vehicle slows and lessens in intensity as the vehicle slows.

Unaffected by brakes. and definitely feels like it's coming from the rear.

at 50 the whole vehicle feels like it is gong to shake apart.

This happened when we were on a trip in August. It went away and there was no vibration for a 200 mile jaunt last week. It showed up again yesterday.

My thoughts about causes are:
-bearings. Maybe though there is no squealing and it is a pretty big 'thunka thunka thunka'

-CV joint. New CV joints installed less than 1,000 miles ago. Though I did have an issue wherein one of the CV joints came completely undone from it's mounting, (all of the bolts came out). Perhaps there is a flat spot on one of the ball bearings in there that occasionally rotates around?...? or some other damage was done to the cv.
Seems that if this were the case it would respond to accel or decel.

I plan on jacking it up in the rear and rotating the wheels to see if there is any indication.

Ideas on what to look for?

[Westy78]

My first thought was tread separation in one of your tires. How old are they? Seems like that would be a constant though. Not intermittent.

[dtrumbo]

My first thought was tread separation in one of your tires. How old are they? Seems like that would be a constant though. Not intermittent.

I think you're on to something here. In high school I had a '79 Camaro (who didn't?) that had a belt that separated. It would only rear it's ugly head at ... ahem... a certain speed. Are ya due for new shoes? What do the kids call 'em these days... kicks?