I beiee some here are unsure how a dual circuit master cylinder works. They are under the impression that both pistons are connected to the pushrod. Only one piston is actually connected to the pushrod,the other is activated by hydraulic pressure and is free floating in the bore. The only time the pistons actually contact each other is when there is a failure of one circuit(pimar circuit, closest to the pushrod). This allowed the hydraulic cushion between pistons to fail and they then stack solid