Oh, and by the way, the piston assemblies in the rear braking system ARE called "slave cylinders", also known as "wheel cylinders". 
in theory they are a "slave" (ie you have a master and a slave to in a hydraulic system) but in automotive logic
they are referred to as wheel cylinders for all brakes, the slave cylinder is strictly for a clutch components
ALTHOUGH, in 60's era large trucks, 2 to 5 ton, the brake system on those had a "master"cylinder on the firewall, a slave cylinder under the cab that worked the vacuum booster. it was a strange setup but worked, but that has no meaning at all here
