Check to make sure the hydraulic brake hose connecting the calipers are in operational condition. Make sure they did not get twisted, stretched or kinked when re-installed. You might have a problem with the Brake Master Cylinder. Its called residual hydraulic pressure. The causes are, the internal plunger not returning fully when brakes are released, the power booster adjustment rod over adjusted or sludge build up in master cylinder. This may cause the brakes to "drag".