A hydraulic brake assembly for use with a vehicle having brakes with friction elements for stopping the wheels of a vehicle and a supply of hydraulic fluid for the brake assembly, the hydraulic brake assembly including one or more master cylinder assemblies in a brake assembly housing having one or more housing bores arranged side-by-side for housing a respective master cylinder assembly; each of the one or more master cylinder assemblies comprising: a master cylinder piston slidably disposed in the respective housing bore and movable by actuation of a brake pedal between an active position and an inactive position, the master cylinder piston having a first diameter and a second diameter, the first diameter cooperating with the housing bore to define a variable volume quick-fill chamber, the second diameter cooperating with the housing bore to define a variable volume master cylinder chamber, the master cylinder piston including a piston bore communicating with the quick-fill chamber, and a spool slidably disposed within the piston bore, characterised in that the spool is operable in a first mode to direct hydraulic fluid from the quick-fill chamber to the master cylinder chamber and the brakes at a first pressure upon initial movement of the master cylinder piston from the inactive position toward the active position for taking up any clearance between the friction elements of the brakes, and the spool is operable in a second mode on further movement of the master cylinder piston to direct hydraulic fluid from the quick-fill chamber to the supply of hydraulic fluid when pressure in the master cylinder chamber reaches a predefined threshold, and continued movement of the master cylinder piston toward the active position provides hydraulic fluid to the friction elements of the brakes at a second pressure higher than the first pressure. a master cylinder piston slidably disposed in the respective housing bore and movable by actuation of a brake pedal between an active position and an inactive position, the master cylinder piston having a first diameter and a second diameter, the first diameter cooperating with the housing bore to define a variable volume quick-fill chamber, the second diameter cooperating with the housing bore to define a variable volume master cylinder chamber, the master cylinder piston including a piston bore communicating with the quick-fill chamber, and a spool slidably disposed within the piston bore, characterised in that the spool is operable in a first mode to direct hydraulic fluid from the quick-fill chamber to the master cylinder chamber and the brakes at a first pressure upon initial movement of the master cylinder piston from the inactive position toward the active position for taking up any clearance between the friction elements of the brakes, and the spool is operable in a second mode on further movement of the master cylinder piston to direct hydraulic fluid from the quick-fill chamber to the supply of hydraulic fluid when pressure in the master cylinder chamber reaches a predefined threshold, and continued movement of the master cylinder piston toward the active position provides hydraulic fluid to the friction elements of the brakes at a second pressure higher than the first pressure.