In this pic the large reservoir is to the front.
There are 2 pistons that are separated by a void, that when properly bled, full with fluid will not compress.
The pushrod will push the right piston, with the solid fluid void against the left piston, that when properly bled, will apply pressure to that brake system.
If there is a leak in the left system, the pistons move left until the left half of the piston hits a stop, THEN pressure builds in the right system.
If there is a leak in the right system, the right piston will move, build no pressure, and when the coils bind, or some have a protrusion you can just see thru the coils in pic.
After right piston contacts left piston, THEN pressure builds in left system .
That's why pedal "goes to floor", but it actually is just moving till one system can build pressure.
The reason there is a delay when bench bleeding is the pushrod end of the piston has to move enuff to move left half, and with air between the two, you will have no movement of left piston till physical contact, or once bled, the solid filled middle void will move left side .
Hope that helps, - cheers .
Hope that's easier to read than it was to compose, lol !
