Take the pads out and lightly rough up the friction material, using a screwdriver clean the groove between the pad surfaces. Wipe clean the back and edges of the metal pads, add a smear of copper slip to the top and bottom edges of the metal pad (do not get this on the friction material) BMW probably recommend something else but I've always used copper slip? Also wipe down the callipers especially where the pads sit. Do one side at a time encase you need to look at anything and be carful if you push the calliper Pistons back as it could force brake fluid out of the reservoir if it is too full or you move them too far! IMO
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