I have a 1975 W300 PowerWagon, that is powered by a 440,.
I was cruising down the hiway when all at once a viberation occured & I thought that I blew atire..pulled over & everything appeared alright.
There is no visible reason for the viberation, does this vehicle have a balanced fly wheel? it seems that the viberation is in that area? I pulled the dust cover & all seems normal there to?

 

Check U joints and tire balance would be first

 

Check the rims for balance wieghts.

 

check your lug nuts also

 

Is it a engine or driveline vibration???

 

It does it setting still, just by reving the engine

 

I believe it is the engine, is the 440 internaly balanced or does it have a harmonic balancer?

 

Vibrations are the worst problems to solve. It could be the engine or trans. That is an important bit of info. First I would do a compression test & check ign - firing on all 8. Check the timing marks on the balancer . Next check the rocker arms, check for bent push rod? That's the easy stuff. next I would pull the pan and check for a broken piston skirt ? Then I would check the flex plate. IF every thing is ok ? I would consider changing the converter or at least have someone check it

 

it could be anything from tires-driveshaft-wheel bearing. most of time the vibration could be felt from 55-70 mph.