I would say a out of round "warped" rotor. If you only have vibrations while braking that would be the first suspect. Other than that a sticking caliper, or frozen caliper slides could be adding to the problem.

 

can you take a picture of the chunk taken out of the caliper? is it on the piston or the body of the caliper?

 

Here is a picture of the calliper (that I put in about a week ago). The one before this was the same way.

 

My 2004 ram just did the same thing. I did all four brakes and now truck shakes bad getteing off the interstate during braking . so will be getting some rotors this weekend as they do not look to good anyways, just fig I would get off with just a pad change guess not. Good thing is I did get over 90K out of these rotors.

 

I would guess the rotor is bad and the shaking is cracking the ceramic piston. Do both at the same time. I know it sucks but thats the only thing I can think of that would break that.