Bleeding brakes

If the brake lines that were connected to the master cylinder got any air in them while the new one was being installed then you will need to bleed the brakes at each wheel as well.

How to bleed the brakes at the wheels : https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

And here is more basic information on soft brake pedal and pedals that go to the floor: https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Check those articles out, and then try bleeding the brakes at the wheels. If that does not work, then it is possible that you simply got a bad master cylinder.

I usually do each wheel three times, pumping the pedal fifteen times with each iteration, and then it is good. Then I do it a fourth time for good measure.

If there were something going on with the new calipers, it would be due to a leak. You would see the brake fluid leaking out of them without a doubt. The only other thing I can think of is simply that you got a dud of a master cylinder. One or more of the internal seals is allowing fluid to flow by. You would not necessarily know it by simply pushing on the push-rod. Believe it or not, with aftermarket and re-manufactured master cylinders, this happens more than you would believe.

You can also check out this guide: https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Go through it and see if it helps you out.

Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken