About three or four times a year I have to replace my brake springs because they fall off inside the drum while driving. Of course the only way I know they came off is the grinding noise they make as the wheel turns thus making them no longer able to use. I don't understand why they keep coming off. They are kinda stupid proof, You put them on and the tension holds them in place. Why do they keep coming off?
I have had the same thing happen in the past. Someone suggested hooking the spring from the back side so the shoes want to pull towards the backing plate not away. That worked for me. Without seeing the shoes, maybe the cam, lobes, shoes are very worn and not enough tension is pulling on the shoes or wrong springs.
You've got a problem there Will and it's a pretty odd one. Like Mark says for some reason there may not be enough tension on the springs to have them stay in place. It should take a bit of pressure to install them. Putting them on "backwards" is a good option especially if you're using 2 piece shoes for the reason Mark stated. Don't think the hub/drum nuts are in that area to knock them off so it's a puzzlement.
The repro springs are not bent quite right. You have to tweak the ends to make them like the originals.
Will ; You can use this part [see picture] if it do's not help take an rear axle shim.