Benches 500 brake problem

[Hoppy one]

We have had this thing for several years and it’s always worked great. A few weeks ago the brake pedal went to the floor and won’t pump and pressure. I replaced the master cylinder and I still have the same problem. It won’t pump up to bleed the brakes. It still acts like a bad master cylinder. I cannot find any leaks. Any ideas? I’m going to bleed the master cylinder again this weekend. 
thanks

[Carl]

You have a leaky rear brake cylinder.  When air gets in there, it's nearly impossible to bleed the brakes- the pedal just goes to the floor.   But the trick I used was to open the bleeder valve in the rear cylinder, then pump the brakes rapidly until fluid squirts all over the back, then bleed as normal.  The pedal pressure should come right up.  Then don't let the fluid level get low, or replace the rear caliper unit, either way.

[Hoppy one]

Thanks for the help. Would this be both calipers or should I just try each one, one at a time?

[Hoppy one]

I worked at getting the air out of the rear calipers and started to get pressure back to the brake pedal. Once the pressure came back found the leak in the steel line running to the back brakes. Replaced it and all is good, the for the help.