SPONGE BRAKE PEDAL

Since you have change the brake shoes/pads and master cylinder you might want to check the following. Are you sure you have ALL the air is out of the system. Spongy pedal is a classic sign of air in the system. Make sure all the air is out of the system. Did you bench bleed the master cylinder before installation? If not then bench bleed then reinstall. If you did, then start at the right rear wheel, then left rear, right front and finally the left front untill you have all the air out of the system. If there is no air in the system then the brake fluid might be bad and need to be replaced. And finally the only other thing is defective calipers or rubber brake lines. Inspected them and make sure the caliper seals and lines are not swollen, soft or torn.