i have about 10k miles towing on my 33 ft tt thought i would check the brakes and pulled drum of to my surprise i only one wheel had any brake lining left i was stopping with only 1 wheel brake ...
Have seen several where the linings come off the shoe itself then break into small enough pieces to come out of the drum. Most found when checking wheel bearings and not a brake complaint. seems like the bonding agent failed to hold the lining. Some still had the lining loose inside the drum.