I've got an '01 T5 that I had to replace the ball-joint on. Tried the hammer and punch method and I just couldn't extract the ball-joint from knuckle. I also have a slide hammer but it was just too long to get it to work properly with the car on jack stands.

Then I realized that since I'm upgrading to XC90 calipers/rotors and replacing the hub anyway, thought it best to just take the whole knuckle assembly off the car.

Turns out, the thread for the ball joint is the same as the wheel hub. I just threaded the old wheel hub onto the ball-joint. Swung the assembly and gave the attached hub a good whack against the ground, ansd the ball-joint came clean off.
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So if anyone is planning to have the knuckle off to do the hub and ball-joint in conjunction, this is super easy and doesn't require any special tools ie air chisel or slide hammer. Old hub threaded onto ball-joint.