Originally Posted by SquidPuppet

It probably has a Shimano CB-E110. Coaster brakes can be funky to disassemble and reassemble if you go at it the wrong way. And often people will attack it from the wrong end because the correct end is counter intuitive. If you know a few tricks it's easier than tying your shoelace. If you run into any snags or hiccups along the way, shoot me a PM and I'll run you through it.

Be careful with youtube videos. There are many that do it the hard way. It gets done, but their methods are clumsy, redundant, messy and time consuming.

Also, and this is critical, do something to completely immobilize the strap. That small amount of up and down motion repeats itself every time you transition from accelerating to braking and vice versa. Every time. That's what caused that big nut to work itself free. Make a shim out of soda can or whatever it takes so there is no slop between the strap and the chain stay. Or you can measure the diameter of your chain stay and buy a snazzy new Sturmy Archer strap in the right size for just a few bucks. And get your self a bigger replacement bolt for the strap if there is slop between the bolt and the strap/arm hole. You want that bolt to be snug in the hole.