Brakes on 88 Honda work fine in cold weather, but very poorly in warm weather ?

[austinrobert19]

It's my daughters car so I'm relaying information as I'm hearing it. I've replaced the front brakes about a year ago and everything seemed to work fine. She had mentioned it before and recently we have had some nicer weather and it has come up again. The fluid level is good and they have been bled. Bad Master Cylinder????? - or something else