If the pedal will not return, it seems to me that the pedal is directly coupled to the master piston, in both directions of its travel. And since the pedal would not return, it seems likely that the piston got stuck in that dirty area forward of the piston's usual travel. So why did the pedal go to the floor?
Possibilities-
1. Debris in fluid, causing the master piston seal to fail. (No fluid displacement)?
2. Expanding brake lines? "Blowing up like balloons"?
3. Vapor in master cylinder, due to boiling fluid?
4. Leaks after master cylinder?
5. Clogged "by-pass port"?
Once my 1980 F250's pedal went to the floor. (No ABS). The shop said the master cylinder had a by-pass port, that got clogged. They flushed the system, and this seemed to be the answer.
So what does a by-pass port do? Let fluid that sneaks by the back side of the master piston back into the system? That would sound reasonable, because no seal is 100%. If fluid weeps past the master piston seal, it would get trapped behind the piston, and it would have to leak out somewhere, like into the vacuum assist plenum. So I guess a by-pass port is a one-way passage, that allows seal run-off to be admitted back into the system, when the brkae pedal is released.
If it has a by-pass port for this purpose, then it will have a check valve, that only allows the passage way, (or port), to be open only when the pedal is released. This valve may be held open by debris, and if it is stuck open, then the pedal could go to the floor. The fluid would just go around the piston, filling up the master cylinder on the back side of the piston when the pedal is pushed, and this fluid would return to the front side when the pedal is released. (Unless the piston gets stuck in the dirty un-traveled area near the end of the cylinder, forward of the pistons' usual travel). In which case the pedal would not return, assuming it is directly coupled to the master piston, in both directions of travel.
Another thought occured to me-
The sensors are reading a gear looking thingy, in the hub area. This gear makes the pulses read by the sensors, as it rotates and each "tooth" passes the sensor, causing the generation of pulses, read by the computer, and compared to vehicle speed, for servo actuation if needed. Both the gear and the sensor are exposed, and being magnetic, they can pick up ferrous materials from the road.
Last time I looked at a hub on mine, the sensor was covered with incidental metal shavings and debris.
If the sensors are reading the ferrous teeth, then they can also read ferrous debris! If the debris is not moving, like when the sensor is covered with magnetic material, then the sensor will not be reading pulses at all. It will instead just be in a static state of either on or off, but won't toggle, presumably. No pulses could be interpreted by the computer as a lack of wheel rotation, or as an outright sensor failure, if the software has any level of safety redundancy written in.
I'm not sure if the accumulated crap in that area can cause a malfunction, but it seems reasonable to clean it off periodically to avoid the possibility of the brakes from screwing up.
Anybody heard of accumulated ferrous debris affecting sensor or computer operation?
How 'bout a by-pass port? Our Vipers got that?
Maybe I'll have to write Herb Helbig, for publication in the next Viper Quarterly.
Question- Uh, Herb, why are brakes failing in the 2001 Vipers?
Answer- What do you mean? Brakes can fail on any car, in any model year. Next question?