I have a 1993 Jeep Grand Cherokee Laredo. There is a "violent" vibration that occurs only when you are going 40-60 MPH and you hit a bump or pot hole on the highway. The front end begins to vibrate and the entire car shakes. If you coast to under 40MPH it stops and you can resume driving normally again until you hit another bump. You can drive many miles with no issue on a smooth road. When you hit small bumps at lower speeds the front end feels loose, but the symptom otherwise does not occur. This problem did not start until the front disk brakes and rotors were replaced. I had the front end checked, lug nuts, tires, play in wheels while on lift, and anything else the mechanic could think of to no avail. Any suggestions as to where to look and what this might be.