B13 Sentra Wobbly Wheel?

My Sentra's front left wheel has started to wobble. It doesn't wobble left or right; it wobbles front to back. I can stop, put the emergency brake on, get out, grab my wheel and shake it forward and backward. I can feel it when I drive, too. Does anybody know what could be causing this?

Nevermind. I found out what was wrong. My sway bar bushing was just about broken. If anybody else has this problem, I have pictures and a video of the problem.