Did you clean the brake adjusters and back off both sides. Have you cleaned the wheel cylinders on both sides. Their is a pressure differential valve for the rear brakes you could try a scrap yard unit. Are the brake springs the same on both sides. The master cylinder can cause problems. Try loosening a bleed screw at the master cylinder does it have pressure. Normally each side of the master cylinder will feed one front and one rear wheel. This is the line to check for pressure for the drivers side. Is a caliper also hanging up.