OK, after years of wondering what this is and hearing other also have it, I found the source. Dunno if it's the same on yours as I've heard some having to tighten a body mount there.
I was on a road that had the perfect bump frequency and kept feeling the shudder in the floor. Started moving my feet around a bit and coincidentally my ankle was brushing the brake pedal when it happend again. It's the brake pedal! It won't do it if your foot is touching it because what's happening is there is a mild frame flex/movement that happens to be the resonant frequency of the brake pedal and its steel lever. So even slight contact damps it enough that it won't happen. You have to *ever* so slightly be grazing the pedal's rearmost edge. If you try the right edge it will just move a bit until your leg/ankle limits its shudder and you won't get the full effect. But contact with the rear edge will let it slide back and forth across your skin.
So, in my truck it's the brake pedal shuddering back and forth over the right bumps. It actually causes quite a ruckus as once it gets going it has the power to make other things wiggle down there.
Should be a piece of cake to eliminate because all I'll have to do is change the mass of the pedal enough that it's no longer in the resonant frequency of the source. I'll duct tape something to the back of the pedal for a bit.
DougM
I was on a road that had the perfect bump frequency and kept feeling the shudder in the floor. Started moving my feet around a bit and coincidentally my ankle was brushing the brake pedal when it happend again. It's the brake pedal! It won't do it if your foot is touching it because what's happening is there is a mild frame flex/movement that happens to be the resonant frequency of the brake pedal and its steel lever. So even slight contact damps it enough that it won't happen. You have to *ever* so slightly be grazing the pedal's rearmost edge. If you try the right edge it will just move a bit until your leg/ankle limits its shudder and you won't get the full effect. But contact with the rear edge will let it slide back and forth across your skin.
So, in my truck it's the brake pedal shuddering back and forth over the right bumps. It actually causes quite a ruckus as once it gets going it has the power to make other things wiggle down there.
Should be a piece of cake to eliminate because all I'll have to do is change the mass of the pedal enough that it's no longer in the resonant frequency of the source. I'll duct tape something to the back of the pedal for a bit.
DougM
