1999 Ford Escort while braking, shakes

Hi and thanks in advance. Lately while slowing down and braking while making even the slightest turn, such as into a parking space, my car sarts to shudder and make thunking noises. When I am the passenger I feel it under my feet. If I am driving, I don't notice where the thunking is, I guess its everywhere. It doesn't seem to affect the ability to stop, but it sure is scary! I don't do a lot of highway driving, so it isn't driven at much more than 45 MPH for the mosdt part. My husband has gotten under the car, taken off the wheels and checked everything, with no luck. But he is a great mechanic, so if it was something ordinary, he would have found it.
Please help!
Thanks,
Ali (my 1st time here, think its a great site)