1992 Ford F-150 It violently shakes when you hit a bump in t

Shakes or Wobbles problem
1992 Ford F150 V8 Two Wheel Drive Automatic

My sister in law uses my truck the most and she told me about a shaking problem it had alittle while back. I went and tested it out and when I went alittle fast over a bump it started shaking violently until I let off the gas and slowed down a bit. I took a look under the truck and everything seems to be in place I dont see anything loose. The shake mostly seem to be coming from the bed of the truck, but its hard to tell exactly where.