For Audi Q3 8U 2011-2018 SUV. for Audi Q3 8UB, 8UG 2011-2014 SUV. for VW Passat CC 357 2008-2012 Coupe. The job of the caliper is to slow the car's wheels by creating friction with the rotors. When you step on the brake, brake fluid from the master cylinder creates hydraulic pressure on one pistons in the brake caliper, forcing the pads against the rotor.