Help my baby is sick!

I went over some railroad-tracks a little too fast and there was a left hand turn right beyond them, I had to take, and in the middle of the turn I heard a really load clunk.

The part I F-D UP is connected to the rear left tire. All I really know about this part is that it is plastic and it is broken. Now everytime that poor tire has to go over a small bump, or when I stop, or make a left hand turn the poor little guy goes clunk clunk. I know it is not good to be driving on it, but circumstances require me to do so. I need to get this fixed soon! Can you help me?!? I need to know what I did, what the part is called, and where I should get it. Also anything else you might think would help me. PLEASE HELP ME FIX MY BABY!!!!!!!!!

By the way... She is a 1990 300E

Thank you so much!!