brake help needed

I have seen this happen when the pedal doesn't let the master cylinder pedal come back. Possible wrong piston in the cyl. or rod not installed correctly. This can be diagnosed easily by backing off the master cyl. attachment nuts about a 1/4 inch evenly and try bleeding it then. But first try this, reset your proportioning valve by pushing the button opposite of the brake failure warning switch on the proportioning valve. I forgot about this, try this first and then go to loosening the cyl. if this don't work . Good luck , Maybe a bad cyl.