Two biggies...shoes ground to fit actual diameter of drum, and BOTH adjustments made by the book, look in your service bulletins or in Rumbleseat's free online book.
First, the shoes get centered, then after that (until shoes are changed) minor adjustment for wear is done with upper adjustment only. Upper adjustment alone will not do the job until lower has been set right.
Basic adjustment is to get shoes as close to drums as possible without drag.
Your '40's have the double adjustment system, postwar '46-8 no.