As far as I know, there was only one manufacturer that Sears used that was considered a clunker, there were only 3 models made and only for a very short time. Those were the machines made by Chrysler/New Process Gear. I really don't know much about the pre WWII machines but the post war Japanese Kenmores were all good solid, sturdy machines that don't get enough attention, probably because most of them didn't have the good looks of other Japanese machines.
Cari