Anyone ever have trouble with the rear brake suddenly not working?

My dad used to own this bike and he said it would randomly not work, and he tried bleeding it over and over.

When i got the bike i completely rebuilt the caliper, then bled it on the floor so no air bubbles would be trapped.

Tonight i installed new brake pads, now the brake doesn't work...

I'm seriously thinking of just rebuilding/replacing the master cylinder...

James

 

Did the pad spring above the pads fall out when you changed them? If the pad spring is rotated 180 degrees from its correct position, it will push the pad on the brake piston side away from the brake rotor. You can bleed the thing forever but the pedal will always be soft. Don't ask me how I know.
You can determine the correct orientation by looking at the rear brake microfiche on the ron ayers site.
Could you be clearer about what the malfunction is? I know it sounds stupid to ask because, after all, in how many ways can a brake not work? If it's not stopping the wheel from turning, it's not working.
Just changing the pads should have no effect on the operation of the master cylinder.