Greetings

I have a 89 240DL that had the front calipers rust on me last year. I switched the front with rebuilt from the local parts store. I couldn't get the rear driver side to bleed (it was January and I live in Northern Maine). After spending a few hours in below zero weather I gave up and waited until now to start this project again. I noticed the master was dripping fluid from the bottom of the tank. Replaced the Master cylinder(new) and brake buster(used). Still couldn't get the brakes to bleed right. After reading multiple blogs on this web sit I learned that one of the rebuilt calipers was a inner and outer mismatch. I switched the front calipers with working ones from my 87 240 that died yesterday. The breaks bleed fine. Everything seemed ok until I started the car to test drive it and the pedal went straight to the floor with no resistance. When I turn the car off the pedal feels normal. Any ideas on what to do next?