I had the same problem. Hit a pothole and the trailer acted like a rocket try to take off. Bounced all over the place. Was having a terrible time keeping tires on the trailer, going through a set every year. Checked the axle straight. Replaced hubs, didn't help. Change tire brand didn't help. Was out greasing the wheel bearings and just happened to glance at the springs. On one side both sets of bushings on the trailer were gone, just the bolts were there. Replaced all the bushings on both sides and this help with the trailer bouncing. It still bounces but not as bad.