Ok, probably a dumb question, but how do you know when your ball joints are going bad? (what driving condition prompts you to check them?)
Most people start looking at their ball joints after having an episode of death wobble and have verified that their track bar bolts and bushings are good. Although, there are things you can do to check them before you get to that point.
If you have a dial indicator, it will be the best way to measure ball joint play. But, there are things you can do to check it without one and, if they are really bad, you won't need one.
Here what you do:
1. From the axle, use a good floor jack to lift one of your tire off the ground. If you don't have a good floor jack, set your axle on a jack stand to hold it up securely in place.
2. From the side, place a long pry bar under the tire and have someone lift it up and down while you watch the lower ball joint for axial (up and down) movement. Any movement more than 0.050" is too much and would indicate that your ball joint is bad. Of course, if you can see this movement with your eyes, it's definitely bad.
3. Next, grab the tire at the 12 and 6 o'clock position and try to rock it back and forth while you have someone watch the upper joint for any movement. Any radial (side-to-side) movement more than 0.060" is too much. Again, if you can see the movement with your eyes and without any dial indicator, it's probably bad as well.
To be clear, it doesn't take much to make your ball joints bad and that's why you really want to use a dial indicator to test them out. You can rent one for free at Autozone and the like.