An electro-hydraulic brake system containing four isolation piston assemblies each of which is comprised of a cylinder, a piston, and a pair of hydraulic lines. The cylinder has only two apertures, and the piston is disposed in the cylinder. The first hydraulic line communicates between a wheel brake and a first side of the piston through one of the apertures. The second hydraulic line communicates between an accumulator and a second side of the piston through the other of the apertures. The system components are arranged in a compact, easy to manufacture package.