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So, I'm driving down the road at about 35 mph and if I hit a little bump in the road the front end starts shaking as if the whole truck is about to explode. I have to slam on the brakes and slow down to about 20 mph so that it stops. Other than hitting bumps in the 30-40 mph range the truck drives fine. Any suggestions as to what this might be?
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I won't give a long technical rendition of how resonance works as a force multiplier against the natural frequency of a part or system of parts. Last time (s) I did it seemed like wasted effort. Anyway I will cut to the chase. You have mechanical looseness in your front end. Once excited by a bump or RR track all it takes is a much smaller source force, like slight tire imbalance or road energy, to keep it at a high amplitude. Bet it goes like this. You hit a sudden and severe pot hole, RR track or sharp bump and that gets the force going. Then no matter what you do it keeps on going until you come to an almost complete stop. Can be scary. Example, someone strikes a big bell with a large hammer, it resonates net more energy than the input as a force multiplier and then someone uses a smaller hammer to keep the energy excited so it doesn't degrade. That is what vibration is the mechanical degradations of energy. Your problem is most likely looseness in your ball joints, tie rod ends and related front end parts like shocks, not likely the steering gear but it could be in combination with other things. The steering damper, if anything would damp, but not be capable of critically damping, the energy. Plain as mud? Long and short of it is to find the looseness and fix it and or lower the source force because there is always going to be a pothole or RR track somewhere can't get rid of those. Sometimes it is a matter of balancing some over-sized tires a lot better in the couple plane. That is often simpler than stiffening, removing looseness, the front end or front end parts. 106