Originally Posted by thad

So after rebuilding the master cylinder, flushing and bleeding the system, checking the booster push rod play, replacing pads and rotors, bedding and driving for a few days, I've come to the conclusion that the issue (at least mine) is not with the hydraulics. after trying a few different things with my driving style I've noticed a very firm and consistent pedal feel when I have rapidly transitioned from full acceleration (at peak boost) to full braking, or when I left foot brake. This all points to the booster. From what i can tell the booster is just slow to react to changes in manifold pressure, so when you apply the brakes after having already lifted off the throttle, the booster is assisting, and you get a lower pedal that requires less effort, with one or two pumps, the pressure differential from one side of the booster's diaphragm to the other is all but eliminated and the pedal firms up. then after a second or two of idle vacuum the booster assist returns. It's just quick enough at losing vacuum and just slow enough at returning to vacuum that it feels inconsistent.