A master cylinder includes a restraining device arranged between the first and second pistons for preventing the return spring from being compressed and expanded beyond a certain extent. The restraining device includes a first, substantially sleeve-shaped component and a second, substantially pin-shaped component. The pin-shaped component includes a flange which projects radially outwards. The sleeve-shaped component includes a first receiving flange which positively interacts with the flange of the pin-shaped component. The sleeve-shaped component includes at least one introduction opening which enables the flange on the pin-shaped component to be laterally introduced into the sleeve-shaped component. The end of the sleeve-shaped component includes a second receiving flange which positively interacts with a flanged projection on the second piston which projects radially outwards. The sleeve-shaped component includes the at least one introduction opening which enables the flange provided on the second piston to be laterally introduced into the sleeve-shaped component.

A dual master cylinder for a vehicle brake system includes a housing having a housing bore with a open end and a closed end. The open end has a piston stop. Two pistons are reciprocably received in the housing bore and define therewith a first pressurizing chamber between the pistons and a second pressurizing chamber between the second piston and the housing bore closed end. Each piston has a piston cavity opening into the respective pressurizing chamber. A first locator member and a second locator member are respectively received in the pressurizing chambers and slidably mounted in the piston cavities of the respective pistons. The first locator member projects into engagement with the rear wall of the second piston and the second locator member projects into engagement with the housing to establish the pistons at respective normal rest positions enabling fluid communication through the port between the fluid reservoir and the respective chambers. A detent associated with each of the locator members permit the collapse of the locator members within the respective piston cavity upon a first occurring forward movement of the pistons forward of the respective normal rest positions, and further acts to retain the locator members in their respective collapsed states. With the locator members remaining in the cavities, the pistons are freed for fore and aft reciprocable movement within the housing during subsequent operation of the master cylinder.