maybe, engine mounts broken or loose.

Have a look at how much engine moves when reving engine, car parked
in neutral.

and further, have handbrake on hard, car in 3 or 4th, helper in
driver's seat, and you looking at engine as helper lets out clutch
medium slow, and eventually stalls engine. That will put strain on
mounts.

its just a guess, but not to hard to check out and discount/confirm.

alistair

On 6-Oct-10, at 11:06 AM, Zach Hale wrote:

Hey all,

I've noticed over the last 2-3 months in my 85 Vanagon when I have a
strong head wind, accelerating on the highway especially with an
incline that the car gets into a vibration that ends generally no more
than 10 seconds later either after I've gone over the hump or have let
off on the gas to strain the engine less. I don't want to assume it
has to do with something connected to the engine, but those are the
symptoms as far as I can reason. I'm writing in because now it's felt
like it has happened a couple times when going in the 30-40 mph range
just around town (normally hard to tell due to our wretched Seattle
streets). Note that this does not seem to be a symptom of driving at
low rpms as I've always been going at least around 2500 rpm when this
happens.

3500 miles ago I had new tires put on it (recently rotated), my power
steering rack replaced, and an alignment done.

I'm not sure what to look into or check. Does anybody have any ideas
for what to suspect? Should it be cause for concern?

Thanks!
Zach