Motorcycle Repair: Brakes, master cylinder, plunger

Question
QUESTION: We have rebuilt the bike, changing everything out,  now the only problem is within 30 mins of running, the brake on the back will "freeze" up, and you have to sit and wait 45 mins for it to cool down before you can move the bike.   Everything has been changed, all rubber hoses changed to the braided kind, etc..  Even if you test it and do not use the rear broke, only  the front,  the rear will still lock up.   We are at a loss for why.. no one seems to have an answer.. HELP !!!!!!!

ANSWER: What year and model?
Mike

---------- FOLLOW-UP ----------

QUESTION: Guess that would help !! Sorry blonde Moment ... 1980 Wide-Glide.  Thanks ! Beth

Answer
Sounds like the puck in the caliber is sticking. It should release when you let off the lever. I would remov ethe caliber and check it.The puck should work smoothly. If it is ok, then check the master cylinder for a plunger that is sticking
Good luck and happy riding
Mike