I was helping someone at the hobby shop here on base the other day with the brakes on his '01 C5. When we pulled the rear rotors off the car I noticed that the center of the rotor has an integrated drum with brake cylinders and everything. We both didn't know what or why they were there but I assumed it had something to do with the parking brake. I can't see those working as a supplement to the actual caliper itself. Anyone know what I'm talking 'bout.