Classic/Antique Car Repair: 59 plymouth, coarse file, long hope

Question
Trying to restore '59 Plymouth I purchased several months ago.  Front passenger drum brake keeps locking.  I've had new cylinders and some new lines put in all around.  Still locking.  Tends to lock on humid days, but not limited to humidity.  Locks on cold days too (though car is garage kept).  Sometimes goes away after a short while of driving. Many other times doesn't go away.  Keep taking to my mechanic.  He takes wheel off, says things look OK (pad and drum), puts wheel back on and brake works fine until next time.  Have tested for environmental influence by moving car from one to other side of garage, front in/back in -- still locks on the one wheel.  Is awful -- essentially can't drive it at this point.  What should I do or what should I suggest that my mechanic do?  Anything you can advise will be greatly appreciated.

Jim

Answer
Ok try this, it has worked for us many times. In a word, champher the very corners of the shoe fiber itself. I will try to explain. This is shaving off just the corner of the brake material. We usually did this with a coarse file and push it crosscut on the very top and bottom of the material.

I am going to try to explain this abstractly. If you can imagine the brake liner material (not the metal part) laid out flat it would be a small pad about 11" long, 1 3/4" wide and 3/8" thick. If you cut the ends at a 45degree angle, the bottom edge would still be 11" long, but the top surface would be about 10 1/2" long. Hope you understand.