This article provides a step-by-step procedure to overhaul the M635 brake calipers i.e. clean the pistons and install new o-rings and rubbers. The article may also be of use when replacing brake discs or pads. I got to this exercise after experiencing a noisy trembling at the front, at speeds above 90 km/h (which occur more often than not.....). Jacking the front up revealed that the left wheel could hardly be rotated at all by hand. I took another test drive and measured the temperature of all discs, which was 50 degrees Celsius for the rear, 110 for the right front but 160 for the left front disc..... 1) Preparation: - overhaul sets (item 7 in the picture, dustcovers, springs and o-rings) - optionally a new brake line kit. I used steel inforced brake lines - ATE brake cilinder paste (Bremszylinder pasta) - 7mm and 19mm socket wrenches - 14mm open wrench - prying rod (an 8 inch screwdriver will do) - rubber cap to top the brake line - hammer and punch (to drive out the sp