>The car took off, but vibrated
>pretty harshly. It seemed to be coming from the entire rear end - that is,
>like it was hopping on the pavement. Not violently or slowly. But firmly
>and quickly - like two thumps per second.
Its not the springs.
What speed = 2 thumps/sec?
Could be U-joints/loose clamp bolts. Could be loose hubs or wheel nuts. Could loose crown wheel bolts. Could be loose pinion.
Whatever the problem, it should de diagnosable without getting too intimate with the car, or removing anything.
A more exotic problem I faced, was where the car would vibrate terribly at some speeds, but at random times. The problem turned out that the driveshaft bushing in the tail housing of the tranny had spun out of the tail, and the bushing was just sitting on the yoke of the driveshaft. The vibration went away when I pushed the bush back into the tranny. Ultimately I had the replace the tranny due to the damage made to the tail housing.
Good luck Jay,
Jarrid Gross