1999 Jeep Grand Cherokee Laredo shaking when braking

106000mi 4.0L 6cyl I have been having a problem with my brakes. The problem is I brake just fine above 60mph and below 45mph it is when I am between there that it occurs. It is almost like the car is going to fall apart sometimes. My jeep begins to shake, the steering wheel and it looks like the front end is shaking as well. Sometimes it is a violent shake most of the time it is just a slight shake. All I have to do is let off the brake and allow it to slow down and reapply the brake if there is anyway that you can help me with this problem it would be much appreciated.