weird brake/suspension problem???

[graphics_monkey]

I have an 84 500SEL with about 260k. Three days ago, I noticed that when I first start my car in the morning, the brake pedal is a little spongy. As I drive to work and the car warms up, the brake pedal gets firmer and firmer, but at 50mph, the car starts shaking pretty violently. I have had the tires balanced, and the pads/rotors checked, and the problem still persists. Could this be two separate issues or are they connected somehow?

When the shaking/shimmy/vibration happens, I pull off to the shoulder, put it in park and turn off the ignition. When I restart the car, it seems to be OK for a few miles, but then the problem happens again.

Any ideas? I'm not much of a mechanic, but maybe your advice could point me in the right direction for repairs.

[jhodg5ck]

When was your brake fluid flushed last? It should have been done recently as the manual calls for it to be flushed every spring.

When was the last time the front end was Rebuilt?

How true are your wheels?

Jonathan