[Dick]

Way back when I needed to replace the brakes on my 87 coach Prevost did not have or sell new shoes with friction material, so I had to buy only friction material from Prevost and rebuild my brakes.

Your drum brakes can be inspected from beneath the coach where you can see the edges of the shoes. Obviously you are looking for thickness of the brake material, but in my case I changed them because they were cracking. The cracks radiated out from the brass fasteners that held the friction material to the shoes.

Another reason to change is if a hub seal has been leaking and the shoes are and have been soaked in grease from the failing hub seal. Often if a hub seal leak is caught early the shoes just have grease on the surface and it can be cleaned off, but if the hub seal has been leaking a long time it is likely the friction material has been absorbing the leaking grease making the brakes on that axle very poor relative to shoes that have not soaked up grease.