This works for cars, I'm not sure if it works for quads too...
Lift the front end and support it on the frame so that the tires dangle freely. Put one hand on top of the tire, one hand on the bottom. Push in (towards the frame) with your top hand while pulling out with the bottom. Do the same, but in reverse (pull out on the top, push in on the bottom) Repeat this process, try to wiggle the wheel to see if there is any play. If the wheel rattles back and forth, in and out, then you most likely have a warn ball joint or worn bearings. Again, I'm not quite sure if this works for quads, try it and see...