[Tommy]

My EM Cobra has C4 suspension including fiberglass monosprings front and back. I've never experienced what you describe, but I did improve my handling by going to adjustable shocks all around. I went with QA1 brand shocks. .... My 63 Corvette coupe has modified suspension with fiberglass monosprings front and rear. They can be adjusted by moving a pivot point along the spring to make the moving portion of the spring either longer or shorter. Look to see if you have such an option. .... Many C2 Corvette guys who switched from stock steel springs to fiberglass springs complain about the stiffness and bumpiness of the ride. Sometimes the problem is that the driver is expecting these old cars to ride like a modern Lexus. Other times a change in shocks can help.

Your description of your problem of too much bounce after a bump leaves me wondering exactly what is happening. If your shocks are not providing much dampening, the spring should deflect a lot at impact with the bump, making for a soft impact. But that same soft dampening would allow a lot of follow up motion as the spring flexed back and forth a few times. On the other hand, if the shock are providing a lot of dampening resistance, the spring will deflect very little and the entire car will rise over the bump making it feel very abrupt to the driver. In that case there should be very little rebound after you pass over the bump. So which sounds more like your situation?