Benz300, a competent mechanic would not let a car leave his shop with the brake system not functioning properly. Demand that the mechanic pull all 4 wheels and verify that the new brake pads are installed properly. Have him explain to you exactly what he did when replacing the brake pads. Unless he opened the bleed valves when retracting the caliper pistons there really should be no need to bleed the brake system. It's best to use a pressure bleeder on MB brake systems. You don't mention new wear sensors; hopefully you bought them for the new brake pads and the mechanic installed them also.

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Fred Hoelzle