GM-GMC: brakes, abs, pedal to floor, fluid leak, abs pump

Question
I've had 2 master cylinders put in in a week & brakes are still going to floor, at first not bad but now getting softer, 1998 gmc 2500 4x4. mechanic cant figure it out says its abs module but not sure. my 1 front left abs sensor or hose to brake system has been broke for a year lights on, never bothered anthing before. any help appreciated. ???

Answer
I wouldn't think your abs sensor has anything to do with it.  There are a number of things that can cause that concern.  One being a fluid leak.  I am sure you would notice if you had a fluid leak that large though.  The second it too much air in the system after installing a new master.  You may need to do an abs system bleed, or automated bleed.  Basically it runs the pump and cycles all the valves to move any air that may be in the abs pump and valves.  There are two bad things about that.  One, you need a GM scanner and two, you will need to fix the abs sensor problem or the system will not perform the auto bleed (usually).  Any of them that I have done will not perform the procedure if there are any diagnostic trouble codes present.
Hope this helps