I' rebuilding an original drum brake master cylinder and I see that there is a threaded hole in the front reservoir. According to the book it is the stop screw for the primary piston. This screw is missing and just want to inquire if this is really needed. I am thinking that pressure when you press the petal will go through the hole back into the reservoir? The function of holding the piston seems dumb as it is held by the other piston and snap ring. Thanks.
