Resonance Source of Front Suspension Wheel Hop?

On smooth roads vehicle exhibits no remarkable vibration except at a
particular speed when a cyclic vibration is of sufficient magnitude to
shake car. Oscillations felt in steering wheel at vibration node.

Occasionally rough roads will initiate this vibration at other speeds.
High speeds not required; I have noticed this phenomenum as low as 30 mph.

Tires are balanced and tested by running wheels on car up to 70 mph true
speed at axle. Out of round and lateral runnout of tires within 1/8 inch.
Shock absorbers (struts) bounced checked on vehicle. One side seems
perfect; other seems weaker, but still functionally active.

My take on this suspension trouble:

The problem is fundamental to the design configuration. The coil springs
resonate and the resonating frequency falls in the operating speed range.
Control of resonation is dependent completely on the shock absorbers. I
think this is a flawed design based on previous experience. I once had a
car with a completely worn out (inactive shock). There was no vibration,
only a boat-like wallowing when the road dipped. In the present case, the
designers failed to recognize the natural oscillation tendencies of the
front suspension. I believe the cure in the design stage would have been
to use a dual spring - a heavy outer spring and a lighter inner spring.
The combination would have no tendency to self-oscillate with energy inputs
and the shock absorber would have largely gone for the ride, needed only to
dampen large excusions as caused by large scale road undulations.

Sound reasonable?

 

Well, the node is where vibration ISN'T felt. Maybe a steering wheel
composed of all nodes is the solution?

 

Sure sounds like a '76 Cordoba to me..