A few weeks ago I got in my 1989 Ford F150 truck and started it. It immediately started shaking violently--things literally jump off the dash. As I started to drive it seemed to "smooth out" a little. I got home and haven't driven any where since. The few times that I have moved it around in the yard it still shakes like crazy. Someone told me that it is the harmonic balancer. Is this an easy fix?

Not too bad on a truck. Can be a real pain on FWD cars.