The big nut on the back is for the axle shafts and will not affect the brake drums themselves. There should be 3 5/16ths bolts that are in the center area of the drum. These bolts go to the axle shafts and when you remove them they release the drum so it can be taken off separate from the shafts. Confusing enough?? I know that they look like that you need to remove the big nut, but don't. If the small bolts are missing, it's not a big deal. Often times, when the brakes were last done, the mechanic left them off. It does not really affect anything if they are not there. Good Luck.