ok so im haveing a strange problem with my brakes that no one can figure out.
my brake pedal was droping to the floor so i put a new master in.
i bench bleed the master and blled the hellouta all the bleeders.
i have no fluid leaks and my brake hose's are in good shape.
so heres the problem when i start the car and shift into first gear or revers (car is stick) the pedal drops to the floor and it takes afew to get pedal again and then itll get pedal again and be fine for a while. now i this is the secound master ive put in it in 2 days i thought maybe the first one was defective but im not so sure no. with the car off i can pump the pedal all damn day and it wont happen, but if i start and drive for a few secounds it happens. ive done about 30 masters and countless brake jobs so this is driveing me crazy. ive and one has had the same issue or any advise please help. ty.

 

maybe a brake booster problem..

 

what brake fluid are you using?
what year make and model car?

 

im useing dot3.
93 honda civic lx.