The brief
The E200 had started squeaking under braking and then grinding, the noise that means the front brakes have run through their friction material. He brought it in, which is the right call, grinding brakes are metal on metal and they don't stop the car the way they should. The front brakes do most of the work on any car. The pads are the wear item, designed to be used up and replaced, and the discs they clamp wear too, thinning and grooving over their life. When the pads go right down, the squeal turns to a grind as the backing plate contacts the disc, which gouges the disc surface. By that point you're not just changing pads, the discs are grooved past serviceable, so the front needs pads and discs together.
The diagnosis
On the lift the front brakes told the story: the pads were down to the backing plate, and the discs were grooved and below minimum thickness from running on metal. The calipers and slides were freed off and checked, they were fine, just the pads and discs gone. The rears still had life. So it was a front axle set: new pads and new discs on both sides together, because you don't fit fresh pads to a grooved, undersized disc, and you do the pair so both sides bite the same.
The work
Both front discs and the worn pads were removed, the hubs cleaned up, and a new genuine Mercedes-spec set of discs and pads fitted, the calipers and slide pins cleaned and greased so they move freely, every fastener torqued to spec. The pads were bedded in properly so they'd grip evenly from the start. A road test confirmed quiet, even, progressive braking with a firm pedal and no pulling.
The outcome
Quiet brakes, a firm pedal, even bite, sharp progressive stopping, and no grinding. The E200 went home stopping properly again. Worn-out pads turn into grooved discs the longer they're left, so doing the front pads and discs as an axle set put the braking back where it should be, the safety job you don't put off.
