The answer is not simple. Most Serie 1 cars have an 18 mm master cylinder. The amount of fluid the plungers displace per mm of travel is some 30% less than the displacement of the Series 2 mbc and about half the displacement of the mbc’s on Flavia and Flaminia. In hydraulics one calculates with surface area rather than diameter.
The series 2 Girling is a different system. Retraction is minimal through the rubber trapezium seal. The pads have a large surface area. The thickness, of which a large parts is steel, is less than the thickness of the pads of the Dunlop system.
The Dunlop pads are much thicker than modern pads. The thickness is friction material which may be compressible. When the Dunlop system was developed the friction material was asbestos. The asbestos insulated the heath from the liquid, did have good friction coefficient and was available in various degrees of hardness.
The softer the material, the more it compresses and the more fluid you have to pump when braking.
Other factors determining the amount of fluid you have to pump are inflation of the flexible hoses, retraction of the pistons in the wheel brake cylinders, flexing of the callipers, wobbling of the discs, wear on the disc. Wear on the disc is always uneven. They wear more towards the centre as there is simply less material there per revolution.
The Green Stuff pads are (were) not always hard enough. I was very happy when I started using them some 10 years ago. Some years later the formula was changed and they became too soft. I hear they are harder again but I had already switched to Yellow Stuff. I still use the Yellow Stuff.
The Dunlop brake system is brilliant. I very much like the Flaminia and Flavia system with the proportional Lockheed servo. If it is 100% in order the braking power and sensitivity is awesome. I also like very much the system as put on the Fulvia, both the system without servo and the system with the servo on the front wheels. It is necessary though to be very very precise. Micrometre precision.
Many complain about the corrosion of the Dunlop wheel brake cylinders. This is solvable. If you want your S1 Fulvia to brake better than most modern cars, that is not the issue. Retraction is the issue. The Dunlop system was developed in the 40’s in a world of drum brakes. Drum brakes have spring retraction. The Dunlop wheel brake cylinders have it too. Very complicated with a pin, a clamp, a double flanged bush, a spring inside the piston, a very precise chamber in the piston, a cover of the hole in the piston which has to be mounted at a very exact position. Manufacturing is complicated and open for many errors. Many parts are inside that wear and can go bad otherwise.
The pods I sell here
https://viva-lancia.com/specials/dunlop ... inders.htm have done away with the complicated retraction. I have the grooves machined such that retraction is practically zero. In fact the pads are pushed back by the disc. The pads push back the pistons just enough to be just free of the disc. The pads keep the disc clean and dry. Very little fluid is needed to press the pads against the disc. Response is instant.
It is important that the pedal is high even during an emergency stop. The reason is that you want some braking power in case one of the circuits looses its fluid. The corresponding chamber in the mbc will be empty. You have to move the pedal down more to compensate.
If you rebuild your braking system it is important to test it with an empty rear circuit and with an empty front circuit.
To avoid rattling and other vibrations stick the 3M material that comes with the pads on the back of the pads. If discs and pods are ok it should not be an issue.
You may need a grinding stone to fit the pads.
The Dunlop system is very good but you have to very precise and buying pads which happen to be on the shelf is a NO NO.