I just swapped the brake lines and front master cylinder off my 81 R100Rt, replacing with new steel lines from spiegler, and a brand new OEM MC. Before the operation the front had no brake pressure due to a leaky MC, with the new MC and the new steel brake lines the front is working great. Before the operation the rear was fine, but I figured I might as well swap the line out since they're probably 30 years old, but after installing and bleeding the rear, it has no pressure. I bled the system for what seemed like hours, but no pressure builds, even once the air bubbles are all gone. I don't mean it is spungy, it is like I have no brakes! With the bleeder closed I have no leaks that I can see. I am sure I did something stupid. Help me out here!