The brakes may begin to squeak at about the 50 percent wear point. This is due to the size and material used for the brake pads and rotors. The brake rotor surfaces become uneven, causing a lip to form at the outer edge. This will generally require replacement of the rotors when the pads are worn (pad life varies depending on driving style and terrain).Google+
Car Problem Reports
Mercedes-Benz S500 Replace Brake Rotors When Pads are Worn and Squeaking
Mercedes-Benz S500 Problem
Average Mileage: 140,800 mi (91,000 mi - 164,000 mi)
Visitor, 2003 Mercedes-Benz S500, 164,000 mi
Brakes squeal with 50% left on pads. MBZ are a piece of crap. Own two and will never, never purchase one again.
Visitor, 2000 Mercedes-Benz S500, 143,000 mi
replaced pads and rotor
I have changed my brake pads and rotors and when I step on the brakes they still continue to sound like a bus. I don't know what else to do at this point.
Front rotors are drilled and usually should be replaced instead of turned on a lathe. Aftermarket rotors and pads are not expensive and have been better for me than the factory parts.