[V8] bad bomb, master cylinder or ?

[gbmarc at cox.net]

I have the exact same symptoms you describe with the brake being hard at the top of the pedal and then sinking down 2 inches before it engages.
It happens usually after the car is first started and for the first couple of brake pushes.
I replaced the master cylinder, and it had no affect whatsoever!!
It almost appears to be ABS related, because I think I can hear the ABS engaging with that grinding pulsing noise very, very slightly on the first trip down my driveway in the morning.
My bomb was replaced about 12,000 miles ago.

I also have the differential locking up at slow speed issue, with the 'ABS-Off' light coming on sporadically.  I have replaced one ABS sensor, (the one with the higher resistance, with also absolutely no affect.

Maybe if I replace the whole car, it will have an affect!!!  :)

mark.