worn front end parts (steering or suspension) could cause a car to shake when appling the brakes.
You probably have rusty/scored brake rotors.
Warped brake rotors........
rear brake drums or rotors are out of round.
Your brake rotors are warped.
the brake rotors are warped. resurface or replace rotors. if the vehicle shakes without applying the brakes, check tire balance.
Your rotors are warped. You need new brake pads and the rotors turned at a machine shop or replaced.
probably brake rotors and pads.
Warped brake rotors/drums.
You probably have severely warped front brake rotors. Machining or replacement of the rotors would be necessary to correct the problem
This is usually a symptom of excessive run-out (warped) on front brake rotor or rotors.
If the car shakes when you press on the brakes, you probably have warpped brake rotors, and the squeak is probably some worn out front brake pads. I would have your rotors checked and either replaced (which Mercedes highly recommends or re-surfaced)
A common reason is that the front rotors have warped. Go check out WikiAnswers on the topic of "warped brake rotors". Rotors should wear out smoothly in normal driving. Use of the brakes that generate lots of heat (hard braking, riding the brakes) will result in warped rotors.