If you have raced your Mustang aggressively, on slicks, or even on the street and especially if your car is a 5-speed, you may have cracked torque boxes. Fox bodies don't have the best chassis to begin with, combined with a V8 and some torque, and you are going to have problems. That is why lower control arm reinforcements or torque box reinforcements were designed to reinforce weak and cracked torque boxes (front lower control arm mounting point).
