Title says it all, truck gets driven at least once a week. (Truck was all of a sudden immobile one evening)

 

Heat and old shoes, possibly other contaminants.

When were the brakes last inspected?

 

Brake shoes are prone to dust since they are enclosed and dust should be cleaned during their life. Riveted shoes like you have should be replaced well beyond the point of wearing down to the rivets. You can see how the rivets are bent and have been dragging. The shoes being dragging on the drum is converted to kinetic energy i.e. heat and very high temps. That temperature and the rivets dragging probably caused that shoe to break and heat bond.

 

Thank you for the replies gentlemen. Yes I admittedly have not inspected the rear brakes for the 3 years I've owned it. Thank you for the added insight to this little lesson learned.

 

it is from low quality shoes, ones that are commonly sold now sadly but there are still quality sets out there.

 

At least your drum wasn’t looking a little too thin