Doesn't the electric motor/pump push the pedal back up?When I activate the dump valves with my scan tool the pedal acts like i think it should, pedal all the way to the floor for each of the 3 sections.
Maybe your motor is stuck. I've heard of other folks pulling the motor apart for cleaning and maybe new brushes. Not something I've ever done.
There's always a pair of "geysers" in the reservoir; there's a bit of fluid that jets up from the cylinder into the reservoir before the passages between the two are covered by the piston seals as they travel forward.I believe the fountain that jets up when I press the pedal is the loss of the take up fluid for the low drag calipers.
How far does the pedal "steadily go down"? If it just keeps going until the pedal is on the floor, that's a sign of an external, or an internal leak.If I jump on the pedal it feels hard but just steadily goes down, I think it is just the restriction of the hole on top of the QTU valve. Once the large piston passes the QTU valve port brake pedal.
If it's only dropping until the QTU valve is covered, I suppose that could be a failed QTU valve.
Have you verified that the calipers in front have pistons that move freely? If the pistons are stiff, the low-pressure/high volume section of the master cylinder won't develop enough pressure to move them. Then the high-pressure section has to flow enough fluid to push the pistons against the rotor, leading to low brake pedal.