I've had this old hammer sitting in storage for a while now. The problem, as you can see, is that it's slightly broken. Well, seriously broken. Fortunately, it's not very difficult to get it back into working order. Here's how I did it:
Most hammers, like this one, are based on a very old and simple design. Basically, the hammer head fits over the top of the handle and a couple wedges are pounded into the wood. This compresses the wood against the inside of the head, thus holding it firmly in place.
Unfortunately, my hammer handle broke inside of the head. This made the head wobbily and likely to fly off at the worst possible time.
You have two options to fix this sort of problem. You can either buy a new handle, or if you're lucky like I was, you can reuse the same handle. My first step was to cut the handle as close to the head as possible. Next, you'll need to hollow the wood out of the head. I ended up using another hammer and an old flathead screwdriver to chisel the wood. If your only hammer is broken, I guess you're out of luck...
If you can't reuse the handle, you'll have to buy a new one. In that case, you can skip this next step. Now if you are reusing the handle, you'll need to reshape the top of it so it can fit snugly inside the head.
Once the top of the handle is the right shape, use a hammer to pound the wedges back in. I made the wedges go with the grain, but I think the correct way is probably against the grain. In other words, make the wedges cut across the direction of the grain.
Make sure everything is secure, and you're all set.