For lack of a better place to start this thread, I'll see if this works.so we had a huge temperature change in the last few days, mid sixties to -14 in four days. Yesterday I had the D250 out and went for the brakes and the pedal headed straight to the floor with some resistance, but on a second pump it felt like normal. A quick look revealed no leaks, the master cylinder was full on fluid, and the problem repeated itself all the way home. I changed the front brake pads and turned the rotors early this summer, never messed with the rears, and so my suspicions are with the master cylinder. Open to all ideas, thanks!