Car vibrates

mercedes-benz
e-class

#1

I have a 300d 1984 Mercedes. I have had a intermittent vibration. The car vibrates after about 10 minutes on the roaf but Sometimes it is a bad vibration and sometimes it is very light. You can feel the shaking in the steering wheel and in the brake pedal when I press on the breaks. I have changed the fuel filters, got new tires, and checked the brakes, and no visable problems. It does the same thing when I am driving home from work. The kicker is that it doesn’t do it everyday. What could this be?