I had an unusual situation develop with my brakes and may also answer some questions that have been on this board before. I have a '91 Mazda Navajo,
186,000 miles, bought used. I had wanted to flush the brake fluid, but time delayed the best laid plans, unfortunately. I noticed over time that the RABS valve wasn't doing it's job, but no codes from the RABS computer. When testing the RABS functions, I'd get rear lockup instead of the pulsing pedal and occaisional chirps.Also, on those few times when I needed to do a panic stop, it seemed like the pedal hit a block of concrete for a couple of seconds, then the brakes would react. This behavior has been reported by several people.
I found that the RABS valve had become so contaminated, that it wasn't working very well at all. In fact, it wouldn't pass much fluid when attempting to bleed the rear brakes.
I took the RABS valve out and flushed it with alcohol, and was able to get some of the service back, but it still wasn't right. I finally was able to get a rebuilt unit and now the brakes are working just fine. The pedal feels so different, now that i's normal, and the anti-lock works just like it's supposed to.
Good idea to test the RABS once in a while, make sure the system is functioning properly.