Brake bleeding problem!

[rwthomas1]

Well, the brakes in my 84'300D WERE working fine but for some reason the rubber grommets that seal the fluid reservior to the master cylinder had become really soft and were leaking brake fluid. I picked up new grommets and dot4 fluid, changed them out and proceeded to bleed the system starting from the wheel farthest from the master and working from there. Here is where it gets wierd. I can bleed the two rear brakes and get a decent pedal but when I bleed the fronts the pedal goes soft, right to the floor! I have tried vacuum bleeding and with a helper and the best I can get is a mediocre pedal and this is bleeding the rears last..... The car is driveable and I can lock 'em up but it ain't anywhere near what it was. The pedal was very firm when I started, what am I missing? I have bled many brake and hydraulic clutch systems and have never had this kind of trouble. Any help would be appreciated. Thanks, RT