[old_master]

If the combination valve shows no resistance, it has shut off one of the hydraulic systems, in your case, probably the rears. Auto parts stores have a tool designed to force the valve to the center position for bleeding purposes. You can try to gravity bleed the rear brakes one at a time. When the fluid runs clear from the rear bleeders, close the bleeders, then push the brake pedal down, the valve should center itself. An alternative procedure to center the valve is to open a front bleeder and give the brake pedal a quick jab. That procedure doesn't always work, especially if there is excessive air in the rear hydraulic system.