Well how do they work.

While I know some earlier hydraulic brakes for bikes had reservoirs as do automobile brake systems, I was imagining the current Shimano brake systems as being a closed system with no reservoir and simply fluid in the lines, brake cylinder and their master cylinder in the levers.

So with no reservoir and no vent, when the levers are released the master cylinder should pull the brake pistons back to their original position. Unlike most automobile brakes that I've worked on that simply relax pressure on the pistons and they only move back an very tiny amount from the rotor.


Regardless, if my brakes are giving me troubles, I'd check the pads and rotors to make certain they are in spec first. Bleeding isn't a normal thing for brakes unless maintenance has been performed on them that allows air to get into the system.

I'll suppose that someone doing a lot of off road biking getting sand, dirt and other crap up on the rotors will eventually cause the seals in the piston to fail or score the cylinder so it will leak.

All the bleeding in the world isn't going to solve the problem then, they'll just continue to get air in them until the seals are fixed or the brake cylinder replaced...... IMO.