What makes the whole car shake all of a sudden?

Answer 1

While an earthquake or hitting a solid object is a possibility, it is much more likely this is the Death Wobble. I capitalize Death Wobble because when it starts you will think the wheels are falling off the Jeep (or whatever lesser vehicle you are driving). The whole front end hammers back and forth, the steering wheels shake, and your passengers look at you like you are a homeless person who made your own car out of a shopping cart and a lawnmower engine. If you haven't truly felt the car was going to come apart you don't have Death Wobble, you just have a shimmy or a shake or a wobble or something similar.

Death Wooble (or DW) often comes from worn control arm bushings, or a loose or worn track bar, or poor alignment, or loose tie rod ends, or a problem with another of the thousands of parts that make up a modern front-end suspension. You might need a new idler arm, or Pitman arm, or maybe your steering box has too much play, or the steering box itself is loose, or your track bar brackets are loose, or possibly you need new ball joints, or maybe it's your wheel bearings, or a tire is coming apart. Hard to say.

You could Google for Death Wobble and your particular make and model of car.