Great news! One of our readers, Matthew Davis, has come up with a way to dampen and CURE the Tundra’s bed bounce cheaply and simply — check out his full explanation and PICTURES below:

Hello everyone. I am the owner of a 2007 Tundra double cab 4X4 with the 5.7 engine. I have noticed the bed vibration since shortly after purchasing the truck in July. I had some time on my hands the other day, so I got up under the truck to see if I could identify the source of the vibration. Those of you who own this truck can go and grab the rear bumper and shake it up and down vigorously and you will observe independent motions of the bed and the cab. I began to realize that the frame of this truck has a harmonic frequency with a pivot point between the engine/transmission area and the rear axle area of the frame. (Visualize a guitar string.) You can get into the bed of the truck and stand directly over the rear axle and jump up and down, and you will find that it is almost impossible to make the same vibration that you can easily achieve by applying pulsating pressure to the bumper or open tailgate.

I thought about the idea of attaching some sort of weight to the rear bumper area, but as I considered the idea, I realized that this would only change the frequency of the vibration, but would not necessarily dampen it. It might even make the vibration more intense in the cab. So I thought about the idea of somehow canceling out the harmonics of the frame by creating a dampening device with a slightly different harmonic frequency attached to the area of the frame behind the rear axle as close to the bumper as possible. The logic here is that if you could CAUSE the frame to vibrate from this point, then it should be possible to DAMPEN the vibration from the same point.

I decided to use the spare tire for this purpose so as not to increase the weight of the vehicle. I lowered the spare tire a few inches from the frame, and I cut out two pieces of high density rubber foam and placed them in between the tire and the part of the frame that the tire is pressed against. (I used one of those kneeling pads that you use for working on hard surfaces on your knees.)

The pad:
Picture of the foam pad used.
(Click for larger view)

Overview of the foam placed between the tire and the frame.
(Click for larger view)

There are four points at which the tire contacts the frame. I placed the foam on the rear points and let the front portion of the tire remain in its original position against the brackets that prevent the tire from moving forward. I then re-tightened the tire to where the foam was snug between the tire and the frame. (The tire should be tight enough that it does not rattle.) The tire holder at the end of the cable is spring loaded so it will accommodate some slight movement. This setup allowed the tire to “jiggle” slightly up and down, but at a frequency slightly higher than that of the frame harmonic. You can “tune” the frequency of the tire by tightening, or loosening the cable. This effectively canceled out most of the frame harmonic on my truck, and made for an amazingly smoother ride over rough, or washboard surfaces.

View from the left (drivers) side of the spare:
A view of the spare tire with foam from the left (or driver's) side.
(Click for larger view)

Not enough detail? See another view from the right side.

It is also much more difficult to “shake” the truck from the tailgate area. Likely, when Toyota comes up with some sort of fix for this problem, it will use this, or a similar principle. In the meantime, the ride quality of my truck is much better. You can rest assured, that the springs are not too stiff, the shocks are not defective, the frame is not weak, and the tires do not cause this as long as they are properly balanced, and not out of round. (An out of balance or defective tire could easily magnify the problem, especially at the speed when the RPM’s of the tire match the frequency of the frame harmonic) Hopefully some of you will find this information helpful.

Matthew told us his years of experience owning a metal fabrication shop helped him realize exactly what was going on with the truck and the “bed bounce” effect. I thought it was interesting to read that a stronger metal frame is more likely to have a harmonic vibration than a weak metal frame…maybe that’s the Tundra’s problem. The frame is too strong.

The foam pad Matthew used is about 2″ thick, and its seems to resemble “closed cell” foam. Amazon sells a pad like Matthew used for $19.99, but if you find a better place to buy it please leave a comment below.

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