I have a 300ex and I just rebuilt the master cylinder, and I put it back together the same way it came off. I cannot get my brakes to prime or bleed properly. I tried pumping it with the bleed screw closed, open the valve and pressing the brake down, then closing it..over and over again. I even left the valve open, in hope of gravity taking place, but to now avail.

When im opening the valve should t he pedal already be pressed down?

 

Yes. Pump it, hold the pedal down, then open and close the bleed screw without letting up on the pedal.

 

It should gravity bleed as well. Make sure the rezzy doesnt run dry, and just open the bleed screw, and wait for the fluid to come out, then start the bleeding procedure. I like to attach a short piece of hose to the bleeder, so theres always a bit of fluid covering the bleeder, just in case the foot lever is released before the bleeder gets closed.

 

Ok, I was opening the screw then pressing down.

 

Thats ok, but just remember it has to be closed, when you release the pedal.

 

Yeah, I did that a thousand times..