Abstract: The pistons, valves and failure warning switch mechanism contained within the bore of a master cylinder are preassembled in a container in kit form. The container provides for correct orientation of the parts in the master cylinder bore so that the failure warning switch actuating mechanism is properly aligned with the failure warning switch. The container is a tube of suitable material having a bore with the various internal parts of the master cylinder preassembled in it. Folding locating arms are attached near the forward end of the tube and normally held in a folded position by a cap and plug which closes the forward tube end. When the kit is ready to be used, the cap and plug are removed, the arms are unfolded, and the arm ends are aligned so that they extend through the bolt holes in the mounting ears of the master cylinder body. The tube bore is in alignment with the rear end of the master cylinder bore.