FJ Engine Bay Body Rips
- Thread starter Thai
- Start date
carlsbadfj
New member
Theory for FJ fender tear
Just my speculation. This is possibly the result of metal fatigue, which can happen quickly or over long periods of time. The energy source causing the fatigue is likely vibration from the road. In essence the body is resonating. In simple terms, think of the infamous Tacoma Narrows bridge disaster (look on Youtube for video). Wind blowing excited the bridge and caused it to resonate, resulting in violent movement and failure.
In the case of the FJ, my theory is that driving on the road (or off road) is excites the metal in the fender (like a guitar string). Between fixed mounting points, it resonates like the Tacoma bridge example, thus causing metal fatigue at the point of greatest movement and metal weakness.
Why would it happen in some FJ's and not others you might ask? Well, for an object to resonate you need an input energy at the right frequency. In the Tacoma Bridge case it was the wind at the right speed. In the FJ case it depends on the speed you typically drive at for longer distances, the road condition, and "damping" factors which would be things like a heavy (or possibly lighter) bumper, type of tires used, etc. Hit the right resonate input combo and wham, you have the torn fender syndrome phenomenon reported.
As for the reduced occurrence in the 4-runner, a longer chassis will have a very difference resonance frequency. It might be much harder to cause it to resonate at the frequency that would cause the damage. A shorter chassis would possibly be more susceptible to this damage.
How could Toyota have avoided this? Very simple. Place the car on a vibration input system (all mfg's use them), and input movement at frequencies simulating what you would see under real conditions at various speeds (they have these profiles). Just a guess, they skipped this process as it takes time and money. We (FJ owners) became the test lab.
Again, just a theory. If it is correct, I smell a big class action lawsuit.
Just my speculation. This is possibly the result of metal fatigue, which can happen quickly or over long periods of time. The energy source causing the fatigue is likely vibration from the road. In essence the body is resonating. In simple terms, think of the infamous Tacoma Narrows bridge disaster (look on Youtube for video). Wind blowing excited the bridge and caused it to resonate, resulting in violent movement and failure.
In the case of the FJ, my theory is that driving on the road (or off road) is excites the metal in the fender (like a guitar string). Between fixed mounting points, it resonates like the Tacoma bridge example, thus causing metal fatigue at the point of greatest movement and metal weakness.
Why would it happen in some FJ's and not others you might ask? Well, for an object to resonate you need an input energy at the right frequency. In the Tacoma Bridge case it was the wind at the right speed. In the FJ case it depends on the speed you typically drive at for longer distances, the road condition, and "damping" factors which would be things like a heavy (or possibly lighter) bumper, type of tires used, etc. Hit the right resonate input combo and wham, you have the torn fender syndrome phenomenon reported.
As for the reduced occurrence in the 4-runner, a longer chassis will have a very difference resonance frequency. It might be much harder to cause it to resonate at the frequency that would cause the damage. A shorter chassis would possibly be more susceptible to this damage.
How could Toyota have avoided this? Very simple. Place the car on a vibration input system (all mfg's use them), and input movement at frequencies simulating what you would see under real conditions at various speeds (they have these profiles). Just a guess, they skipped this process as it takes time and money. We (FJ owners) became the test lab.
Again, just a theory. If it is correct, I smell a big class action lawsuit.
Thai
Elite Member
Seemingly, the 2010 models are "fixed" but only time will tell....
Here are pictures of the extra reinforcements on 5th gen 4runner and 2010-up FJ:
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Last edited:
waketek516
New member
Can those supports be fitted to the 07-09's?
