1980's brake system disc/drum

The residual pressure/joker valve is located behind the "flare seat" in the exit port where the brake line goes .

The modern wheel clinders have a spring and formed metal cup to hold the seal "lips" against the cyl walls, same way a small amount of pressure would .

https://www.forabodiesonly.com/mopar/attachments/0996b43f802313f7-gif.1715373372/