Like DOC said, you likely have bad rotors(warped perhaps). I went through a similar situation with my 126 car about a year ago.
Competent indy garage changed out all rotors and pads - used OEM parts. From highway speed while braking, I experienced front-end shudder.
Took the car back, The owner ordered another set of front rotors. Same thing, Took it back again, This time he reordered both front and rear rotors. Same thing. Reordered another set(all the way around) AGAIN! Finally got it this time.
Apparently his supplier(Caliber MB - Anaheim, Calif) had a bad batch of rotors - some sort of production issue I suppose. It happens.
My 2 cents.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.