Reddit mentions of Powerbuilt 648467 Tie Rod/Ball Joint Separator

Assuming you're talking about square taper, my favourite way is to use what I call the pickle fork. Remove the crank bolts first! Slide it behind the crank arm and smack it with a 4lb sledge hammer. I wouldn't use this method on a crankarm I wanted to save but it doesn't always damage the crankarm. I find it best to the bike upside down on the ground, keeps the hammer away from the rest of the frame.