Ken...I'm not sure how new or old your brake linings are,it sounds to me that they may have become glazed or possibly contaminated by some thing.
Do your brakes work OK otherwise?
It might be an idea to pull a drum and have a look.
It won't hurt to scuff the linings to remove any glazing,and give the drums a good scrub too.
I used to chamfer the leading and trailing edges of the linings,this stopped the shoe 'grabbing'
You can check the condition of all the other parts while you're there.


1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.