Hey Bob
Volume was also a concern of mine. Here is the math I used to determine the surface area of all of my wheel cylinder pistons:
1.5” dia rear cylinders = 1.76 surface area
1.76 x 8 = 14.08
1.125 dia front cylinders = .99 sq”
.99 x 4 = 3.96
Total 18.0 square inches of piston surface.
Now I don’t know how much more travel due to clearances there are in disc vs drum brakes but the donor vehicle has 4 wheel disk with large 3” pistons for a total of 27” square. So I’m under by roughly 10” square in volume.
I still had my crossed the first time I applied the brakes after getting it all together. With the system bled and shoes adjusted I have a nice high and firm pedal that doesn’t take much pedal effort or travel to get stopped, the master has plenty of volume and hyrdroboost provides plenty of pressure.
I did not upgrade to disc front. I have a 1962 with torsion bar suspension, not sure it has ever been done. I believe I read the brake bias is such that the rear does 70% of the braking anyways.
