OK, here is the thing. Disk brakes use a massive amount more fluid in total than drum.
Think about the size difference between a drum brake cylinder and a disk brake caliper.
But, they can be set up so that they use way less per stroke. The reason being the amount of travel the friction surfaces have to do between the two types.
Modern drum brakes are self-actuating. They use the rotational force of the wheels to help them apply more binding force to the drum. All the wheel cylinder does is move them out to touch the drums.
That is why you can get away with such small cylinders. But, it is also the reason you cannot let the shoes touch the drum much at all when not braking.
Calipers are not self-actuating, so the pads can be right up against the rotor with no problems.
Which means even though it takes a lot more fluid to fill the calipers, once they are filled, only a very small amount is needed to move the pads out to full contact.
As the pads wear, the calipers move out more and do not retract as much. But the difference from stroke to stroke is tiny, and is made up when you release the brakes each time.
That is why disk brakes have more fluid in the tank than drum, and why you can get an idea of the amount of wear on your pads by looking at the fluid level.
Its also the reason my Ford brake pedal starts getting lower and lower as the rear brakes wear during hunting season.
The adjusters freeze up due to mud, and the brake cylinders have to move farther and farther out to apply the brakes.
Every so often I slide under and manually adjust them and get my pedal back.
That is also the reason I was asking if there was excessive clearance between the pads and rotors.
Given the size of the calipers, it would not take much drawback to cause excessive pedal travel.
It would not take more than one to do it. That is usually caused by either an overly stiff rubber boot on the caliper that makes the piston retract too far, too much runout on the rotor that drives the pads apart, or a problem with the master that caused some suction on the system when you release the pedal.
If you get too much pedal travel with the smaller cylinder, you can add some of the pressure retaining valves to the system to hold the pistons out.
Many masters have them built in, 2 pounds seems to be standard. Also one of the reasons some masters have to be changed when switching to disks.
Right now, the obvious problem you have is not enough clamping force at the pads.
Whether its caused by air, too much rubber, wrong master size, too weak legs, or fairy farts is only important as to fixing the problem.
Brake pads can only be a patch. Oil soaked pads, Teflon, wood, solid steel, I don't care what those pads are made of, if you clamp them hard enough on that rotor,
its going to stop.
Which is why I was so looking forward to the pressure gauges. They will give an accurate reading as to how much clamping pressure should be being applied to the rotor.
If you have a hard pedal with no boost, then you have no air in the system. If you also have low pressure at the calipers, then the master is too big.
Of course, the leverage factor at the pedal makes a difference, but you have not changed that, so I assume we can ignore it.
Plus I assume your legs will support your body weight, so I don't think the wimp factor comes into play..........
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All in all, if you get enough pressure at the calipers, we can get pedal travel back with check valves if we need it.
I want to find out the fix to this.
