Most likely your alignment is out of whack or bad struts. Could also be the wheels need balancing.
Plugged muffler ot cat converter
If an investigator looked at the skid marks at the crash scene, he could tell how fast you were driving unless the vehicle has ABS brakes, then there would be no skid marks.
Need more info like what is the vehicle doing when it shakes, is it idling in park, driving down the road, braking, driving at highway speeds, etc.
good luck driving 50mph over the ocean
road V.A
Carburator problems -- dirty gas -- water in gas
If your car shakes only when your going a certain speed, it is most likely resonance. Which means your wheel weights are off, or maybe you dont have any. But if it always shakes, it could be a bent rim. The final option, is something else, it could be many different things
there must be a speed limter on it to 50mph
This problemsounds like the tires might need to be rotated and balanced. the car might need to be aligned if the car pulls to the right when you are driving straight.
50mph x 3.5 hours = 175 miles.
around 50mph
Rotors are warped. Have them trued or replaced as necessary. Also replace the brake pads at the same time.