According to Mercedes-Benz, the brake pads on a E320 wear thin after prolonged use of about 40,000 miles and the brakes' built-in wear indicators become exposed to alert the driver that the pads need replacement. If you hear the wear indicators, you should change the brakes as soon as possible to avoid brake damage and possible failure.The wear indicators can gouge the surface of the rotors as well, if the pads are not changed promptly.
Park your Mercedes on a flat surface and turn the engine off. Shift the transmission to park and move to the front of the vehicle. Loosen the lug nuts on the front wheels with a lug wrench.
Lift the vehicle with the jack and place jack stands under the axles for support. Remove the lug nuts and take the wheels off. Remove the sensor wire and sensor wire clips with a pair of pliers. Take note of the position of the wire and clip for insertion later.
Remove the two caliper mounting bolts from the back of the caliper with a 13/16-inch socket and ratchet. Lift the caliper from the rotor and suspend it above the wheel hub with a bungee cord.
Place a flat screwdriver between the brake pads and the rotor. Force the brake pads against the caliper pistons to squeeze them into the side of the caliper. Remove the screwdriver and slide the two brake pads from either side of the brake rotor.
Remove the rotor retaining pin with a 5mm Allen wrench. Strike the roll pins (these are bolts on the rotor) with the hammer on the outside of the rotor. Pull the rotor from the wheel hub and set it aside.
Clean the new rotor with brake parts cleaner and a cloth towel. Slide the new router onto the wheel bolts and roll pins. Replace the rotor retaining pin with the 5mm Allen wrench.
Slide the new brake pads onto the sides on either side of the brake caliper. Replace the caliper and new brake pads over the rotor and screw on the caliper bolts. Replace the wheel onto the wheel bolts and screw on the lug nuts by hand.
Lift the Mercedes with the jack and remove the jack stands. Lower the tires to the ground with the jack and tighten the lug nuts with the lug wrench.