I jack up all 4 corners and open all 4 bleeders and let them gravity drain.......I drain the entire system and then I fill the master cylinder with synthetic brake fluid......while the old fluid is draining I install the new pads....I let some of the new fluid drain and then I close off the bleeders....I close them in the reverse order that I will bleed them.....it works for me....the reason that fluid can try to go out the master cylinder when using a c-clamp is because the piston is moved beyond its normal position(116-123-126) and it forces more fluid into the lines than normal operations will....

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James A. Harris