Brake master cylinder

A brake master cylinder, comprising a main oil cylinder and an oil storing space integrally disposed on a handlebar base of a brake handlebar, the oil storing space having an axial position with respect to the main oil cylinder of the handlebar base, one end of the handlebar base having an oil outlet, which connects to the main oil cylinder via a hydraulic pipe, one end of the handlebar base having an installation hole corresponding to the oil storing space, a piston, which is driven by the brake handlebar, located inside the main oil cylinder, the brake master cylinder being characterized in that:

• a sleeve engaged with the main oil cylinder, located inside the handlebar base, one end of the piston, which relatively stretches into the main oil cylinder, having a first rubber ring, one end of the piston, which relatively stretches into the sleeve, having a second rubber ring;
• a fastening seat located in the installation hole of the handlebar base, the fastening seat having a positioning sheath that stretches into the handlebar base and has an extension portion protruding inwardly towards the oil outlet to engage with the sleeve to cooperatively define the main oil cylinder, a draw bar passing through a central place of the positioning sheath to link the piston and the brake handlebar;
• and
• a leakage prevention component for preventing oil leakage from the main oil cylinder, the leakage prevention component being located between the fastening seat and the handlebar base, a rigid bushing extending from the leakage prevention component to surround the extension portion of the positioning sheath and the sleeve and an inner flange that is disposed to an end of the bushing and engages with the sleeve through a circular groove in the sleeve, so that the bushing and the handlebar base cooperatively define the oil storing space having a fixed volume and the bushing encapsulates the engaged portions of the positioning sheath and the sleeve.