Brake expert's please read

It doesn't take much to clog up a brake line. I would disconnect the rear hose from the hard line going to the front. Then disconnect the hard lines from each of the back calipers. Blow air thru the hose and make sure you have rags or something to catch the fluid coming out of the lines. That way you'll know if the back end is clear. Hopefully you'll find it back there, if not work your way forward. If your brakes worked before then it should be something back there.