Rear Tires Suddenly Lock Up Going 65

Once everything cools down, the brakes won't be grabbing anymore. like during the time that passed when you were cleaning your shorts after the lockup (sorry, just had to). I work on trains and when working on loco's or train cars all it takes is a dragging brake on a wheel to keep you from moving them in the shop. same thing happens, shoes warm up and then stop the loco. we will have moved loco 75 yards then it doesn't want to move anymore.