I have read this thread with some interest and have a few questions. Are they nylon ply tires? When the tires were balanced, were they checked for roundness? You can balance a square block, but it won't ride good. If they are nylon cord bias ply tires or even nylon cord radials, I'm leaning toward a tire out of round or a bad (or flat)cord. Its odd that it only happens at a certain speed which would lead me to suspect a tire, wheel, bent driveshaft, bent axle housing, axle bearing, or bent axle. I think if it was bad shocks, it would do it any sustained speed after hitting even the smallest bump in the road. Joe
