[rohrmann]

Anything is possible, warped from heat, grease on the shoes, and there might be other reasons. That's why I religiously use the exhaust brake system on the truck, and also upgraded to the disc brake system on the trailer. If all your drums are warped, you will probably need to replace all the other components, namely the backing plate assemblies, and the bearings will be part of the drum assemblies. This might be the time to seriously consider upgrading to disc brakes on the trailer, won't be that much more compared to all the normal parts needed if the drums are bad.