To bleed a Master Cylinder -- it is best to be removed from the car --- mounted in a bench vise by one "ear"... I use SOFT JAWS to do this so I don't mar the ear with the vise -- Then you hook up short lines from the ports that go back into the fluid reservoir - and make sure they are fully covered with fluid so when you back stroke they can't suck air -- Then I use a large philips screw driver to drive the piston ALL the way forward many times until no air bubbles come out your lines... You'd be able to see any air as it bubbles out of the short lines you created that are down into the fluid reservoir.
The reason you don't do a MC bleed ON CAR is because you can't drive the piston forward enough with the brake pedal ---- and you can't see into the reservoir while sitting in the car pumping the brake pedal.
Typically this job is done when the MC is first installed --- but I've found lots of people that SAY they did this -- only to discover they actually had no clue what "bench bleeding" is.
Wilwood ships bench bleeding hoses with their master cylinder -- if you still have those they're handy -- although I made my own up out of old brake line and fittings.
Once you get done with that job -- you can then continue on to bleeding your brakes. Bleed them by cracking the furthest brake from the MC -- which would be the passenger REAR -- have someone push on the brake pedal as you crack the bleeder... and have them HOLD the pedal down as you then just snug the bleeder tight - have them push and hold again as you repeat the cracking of the bleeder and tighten and so forth. Making sure you check the MC fluid levels as you do this -- don't let it get to far down! When you get some fluid -- move to the driver rear -- repeat the process - then to the passenger front -- then the driver front........ when you're pedal starts to "firm up" -- repeat the bleeding process once again with the passenger rear and so on.
The pedal should come up quite firm and be able to be pushed on with all your might and it should not go down one iota! And NO air should come out the bleeders at all.
NEVER use old or opened brake fluid! Use brand new just opened fluid for all this process. Don't try to save the fluid that is being bled - it's a CONSUMABLE -- toss it.
Some times I tap (that's gently!) the calipers with a small dead blow hammer as I'm doing all of this in an effort to "shake" any air in the piston area out (bubbles SHOULD float to the top where the bleeder is - in theory anyway).
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