Abstract: A disk brake actuator having a hydraulic slack-adjusting arrangement for maintaining a positive clearance between a brake shoe and a brake disk, includes a cylinder housing having disposed therein a brake-applying spring section, a hydraulic-operated release section, and an actuator piston spindle arrangement operably-connected to the spring section by way of a clutch arrangement. A flange, formed on the actuator piston, acts as a plunger during a brake application and draws a first amount of hydraulic fluid into a first storage area, such first amount corresponding in volumn to the clearance between the brake disk and brake shoe when a nonworn brake shoe is first used. Upon release of the brake, the actuator piston forces the hydraulic fluid back into a second storage area wherein is included a shuttle member movable with a shuttle chamber. Additional hydraulic fluid is drawn from a reservoir when actuator piston movement, beyond the original clearance value, occurs as a result of brake shoe wear.