9in drum brakes

Usually the caliper will prevent the hub and rotor from completely coming off the spindle. If you've ever tried to pull the hub and rotor off without removing the caliper, you'll know what I'm talking about. Some disc brake setups are better than others in preventing that. The disc brake spindles are usually bigger and have bigger bearings, so, they're less likely to have a complete bearing or spindle failure. I've seen many 9" drum brake outer wheel bearings fail. Hubs too. I've only seen one of those spindles shear off the threaded end, but, many that were on the verge of doing so. The most common problem is the outer race spinning in the hub. This can cause the bearing to overheat and fail which can also overheat the spindle. If it's a severe overheat the metal in the spindle will turn purple changing the temper of the metal. It can melt and bend at that point too.