Sponge-y front brakes after replacing front brake pads and calipers. on 1999 Nissan Altima

I replaced the front brake pads and the two front calipers on my '99 Nissan Altima (manual transmission). After bleeding the front lines, and everything seeming to go like it should, I turned the car on and the brake pedal went all the way to the floor. After pumping several times, I was able to get some resistance, but nothing that felt the way it should. We then bled the lines again, this time on all four, and nothing changed. Bled the front again, nothing happened, and I had a mechanic look at it and bleed all four lines again, still with no result. I was able to drive it around, and I can get it to brake and stop, but it certainly doesn't brake as well as it should. I have heard that it could be the master cylindar, or it could be the brake assist assembly behind the cylindar. I want to save money on this as much as I can, so I'm wondering what the best way to get this diagnosed and fixed would be. Can the electronic tests that the guys at Auto Zone detect this? Is there any visible symptom I should see when I check under the hood? And most importantly, is my car safe to drive?

Asked by for the 1999 Nissan Altima
With brakes not working 100% no one should ever tell you that it is safe to drive. You could have air in the system. Does vehicle have ABS brakes? I have seen when both front calipers changed at the same time left and right get mixed up and the bleeder is then on the bottom and will never properly bleed. Also I have seen when old calipers are taken off the pistons compressed without opening the bleeder and the reverse flow of old dirty brake fluid damage ABS or master cylinders. Please call Roy 757-456-0722 if you would like a FREE loaner car/van while we diagnose and repair yours.
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