How do you check them? I should be more specific. I've checked a few old buckets and the joints passed. But the truck was loose as a goose.
I'm going to give a basic description here for the people who don't know how these things work as well as answer your question.
If you watch the video posted, that's the basic procedure, mine is similar. I'm looking for up/down movement. You can force a good one to move if you try hard enough. I have some I use at work as demo's with close to 1/4 inch of play.
Here's for people who donk know how they work.
To understand how they break you have to understand how their built. The steel ball sits in a pocket surrounded by a soft metal. Normally this is bronze. Between the bronze liner and the outer socket is what's called a spring. This normally is a thin, very hard rubber. The spring serves two purpose, one is cushioning the other is keeping tension on the liner to the ball. The ball joint is designed to support up/down and very little side/side as well as allow turning.
Over time the rubber spring becomes brittle, the bronze wears and now we get up down movement. On the street this isn't bad. Dirt on the other hand works it harder, add in the side pull from a front diff and we get wear on the sides also.
Once this is bad enough, they don't really break as much as pull out of the housing. On the street, it has to be worn badly then al it takes is a good bump to unseat it. Off-road the front diff pull can pull it out of one end. That's what happened in the picture. If I had thought to take better pictures, you would have seen where the bottom pulled out and the top was ripped out.
As I stated before, I have seen this three times off road and twice on the street. ALL of them had the same issue, worn and pulled out.
When I posted this, I didn't think it would get the push back it did. Just because someone hasn't seen it doesn't mean it wont happen. If they do see it, it also doesn't mean they took the time to analyze the problem with understanding how the things are assembled.