Are the replacement inner fenders the same as the newer builds?? I drew a line with a marker just so I can monitor it. I hope we can get some other FJers with 07 builds to post pics and updates of their rips/bulges.
Bernd,
I call you sometime this week.
Quote:
makaser previously said:
Yes, between the crumple zones. Although from what I've seen on the replacement innner fenders that are now bulging, the bulge tends to start shoing around the crumple zones. Like you can run your fingers around a normal crumple zone and the panel is flat and then dips down, but on one that is starting the bulge, the crumple zone has a definit ripple around the crumple zone, and then procedes to warp the panel between the two crumple zones.
I will post pics in the next few days with a straight edge up to it so you can see it. Again though, mine is a 5/06 build with almost 23,000 miles on it.
My latest theory regarding this is related to wicked "harmonic vibrations" and how they are handled by the FJ.
Physical structures -- buildings, bridges, automobiles, or aircraft -- can
vibrate. Like a violin, piano, or horn there are certain vibrations that
reinforce one another. These are called resonances. They can cause the
structure to vibrate with large and/or increasing amplitudes. This flexing
puts stress on the same locations of the structure and the moving back and
forth in the same place eventually weakens the structures at these flex
points resulting in damage or failure. In order to obtain a quiet ride in
an automobile designers engineer the suspension to have many different
vibrational modes. Flight and Harmonic Vibrations
I'm sure we've all heard of the stories where soldiers were halted and told to walk casually at their own pace across a bridge because the regular cadence was making the bridge move up and down, putting it in danger of collapsing under them.
One of the things I considered, is the fact that it's happening at a greater rate (or so it seems) to the trucks that don't have aftermarket front bumpers. Is it possible that the addition of the front bumper is somehow attenuating this "natural frequency" of the frame enough to stall the stress cracking.
Another is the fact that I saw the TRD SE that was in the Airborne FJ video on Friday at the dealership. The guy had just sold it to a friend of his and was buying a BMW 3 series.
Quote:
max-9 previously said:
Yea...what he said..
look at how hard this FJ hit ..
It still shows no evidence of any bulges, cracks, nothing as far as damage from the above escapades.
For you guys that are smarter than me about metal fatigue and engineering....can this possibly be as simple as the trucks frame setting up vibrations (when driving on normal roads) that amplify themselves to the point of driving the stress up to the weakest point?
If so, can this be tuned or attenuated by adding weights or rubber/fluid filled dampers (or whatever) somehwere in/on the frame to help at least govern these resonances?
Sorry if this sounds nutty, but I think we have to allow brainstorming to run it's course for our own peace of mind.
I don't think it's as complicated as all that. The reason I say that is because this issue is also effecting the Prado. Although it is on the same platform, it's a very different vehicle otherwise. If it were vibrations causing it, the Prado would probably not be effected in the same way. But the Prados fender bulging is happening in the same place, even though the fenders themselves are very different. This leads me to believe that it has something to do with the components that they share. It's got to have something to do with twisting of the body. So that leads me to believe that it must have something to do with how the body connects to the frame, since the bodies are different, yet those very different bodies are having the exact same symptoms. So, it's got to be the body mounts. If the Prado had the exact same frame and body mounts, and was NOT having this problem, then it would have to be something else. I suppose it could be something in the frame, but I find that hard to believe, although changing the frame, or at least the location of the body mounts might be the answer. If it is, we are all in for some MAJOR work on our rigs I think, because I don't think you can just simply move the body mounts without doing some big changes to the floor of the body. But I could be wrong.
__________________
'07 Voodoo Blue~ 3" RevTech lift, 17" Ultra Goliath wheels w/ 295/70/17 Toyo Open Country MTs, Chopped Body mounts (by Metal Tech), Garvin Wilderness rock rails, HiLift, shovel, and axe roof rack mounts, Bud Built skids, A-Trac hack, 3 additional 12V outlets, including one in the driver's side glove box for my Garmin RINO 530hcx so the wires don't hang across my dash and two more in the center console, Cobra 75 in center console, Scan gauge II, relocated rear breathers,
My latest theory regarding this is related to wicked "harmonic vibrations" and how they are handled by the FJ....I think we have to allow brainstorming to run it's course for our own peace of mind.
What say you?
OK, I can chime in on this. Here's a fair dose of brainstorming to consider.
1. To me, the shape and position of the brackets that connect the inner fenders to the outer fenders suggest that the *give* of the Prado frame was a design consideration in the attachment of the inner and outer fenders. The shape and position of those brackets suggests that computerized Finite Element Analysis (FEA) drove the placement of these internal fender brackets. FEA, rather than physical prototyping, is being used increasingly to speed time-to-production of vehicles from all manufacturers. These virtual prototypes are prone to mistakes or invalid assumptions about forces and geometries.
2. The appearance of the 01/07 modifications to the inner fenders suggest that an effort was made to make them more rigid. This surprises me given what I since have learned about the histories of various vehicles which are exhibiting the rips/cracks. I would have expected some approach to decouple the two halves of the inner fender, rather than couple them more strongly. Therefore I wonder if this design change is sufficient to fully resolve the problem.
3. The strengthening of the inner fender design suggests that the deflection management strategy used in the original fender system design was perhaps too optimistic about the fatigue properties of the inner fenders. In other words, the originial FEA failed to adequately represent some force vector or harmonic vibration (or both) that the inner fenders are subjected to. As a result, the fatigue life of the area where cracking is occuring was overestimated.
3a. I think there are two possibilities: vibration-based fatigue, or event-based fatigue. I'm inclined to pick the 2nd choice. Here's why.
4. Right after taking delivery of my FJC in September 2007, and before I knew much about this issue, entirely by coincidence I drove through an intersection where the FJC's front suspension was completely compressed after crossing over a superelevated (banked) section of the crossroad. This was not an airborne landing like the TRD SE shown in a recent post; instead it was fairly gentle, and would have been a non issue for any normal vehicle. But in the FJC it was just enough to trigger a body-panel response. I definitely heard a slight protest, in the form of a muffled pop, from the upper firewall area behind the dash. I imagined at the time that the body of the vehicle was carrying some of the suspension load, for an instant, during that bottom-out of the front suspension. I imagined that the muffled pop was a panel repositioning itself relative to some panel mounting connection.
5. I checked the next day. No bulges. (Still no bulges today.)
6. I think that the vehicle body can be subjected to a number of full-front-suspension-compression events before the body sheet metal begins to work harden, and then still more cycles before the appearance of the bulges and the fatigue-cracks.
7. Sheet steel will first work-harden before it actually fatigue-cracks. Work hardening is a precondition for the onset of fatigue cracks, and it is also likely the mechanism of the appearance of bulges. Therefore bulges can be expected to occur only in the later stages of the process. There's probably a way to use tuning forks or some other non-destructive vibration test to test for work hardening (pre-bulge) of the cracks/rips area.
8. As a result, I'm now careful not to bottom out the front suspension on my FJC. Its easier to do than any of the alternatives.
Nice posts on the harmonics guys. I love that crap and read it with great interest... filing it away for ****tail parties and such. I couldn't say one way or the other whether it's effecting the fender aprons, but it's a nice addition to the theories and hope Toyota is considering all the well-thought out hypotheses presented on this thread.
In other news, I hit it pretty hard on some trails the other weekend and unintentionally buried the front end a few times. The whoopties snuck up on me. I do have bulging, but it doesn't appear to be any worse than it did the first time I looked and that was at the very beginning of this thread. I should be upgrading the wheels from stock sized ATs sometime in the next month or two and I'll be curious to see if that changes anything at all.
__________________
"I'd like to die in my sleep like my grandfather. Not screaming in terror like the passengers in his car."
In other news, I hit it pretty hard on some trails the other weekend and unintentionally buried the front end a few times. The whoopties snuck up on me. I do have bulging, but it doesn't appear to be any worse than it did the first time I looked and that was at the very beginning of this thread.
Quote:
k44 previously said:
I think there are two possibilities: vibration-based fatigue, or event-based fatigue. I'm inclined to pick the 2nd choice.
After todd's input and many others, I'm more inclined to pick the first choice...(harmonic)vibration based fatigue. Not everyone with the cracks/creases has bottomed the vehicle. Apparently some people with the cracks have never even taken them off the pavement.
After todd's input and many others, I'm more inclined to pick the first choice...(harmonic)vibration based fatigue. Not everyone with the cracks/creases has bottomed the vehicle. Apparently some people with the cracks have never even taken them off the pavement.
Just to chime in: I have well-developed cracks, and have *never* had a serious full-compression incident (although I am carrying lots of added weight, as is listed in my sig). I'm also still under 10k miles.
__________________ Suzie ('SUZ') the '07-6MT-FJC
TLCA#17822 / FCC:KD0ECN / Blue Ribbon Coalition / Navy League#101495511
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Thanks To: BajaRack, BF Goodrich, Budbuilt, Camping Labs, Engel, KC Lighting, Lucrum Industries, Powertank, ProComp Wheels, Springtail Solutions, Tuffy Storage, Underdog Racing Development, Valentine One, Yaesu Radios, Outrider Suspension Armor and TOYOTA
Just to chime in: I have well-developed cracks, and have *never* had a serious full-compression incident (although I am carrying lots of added weight, as is listed in my sig). I'm also still under 10k miles.
SPINCYCLE, dude sorry to hear the issue on your rig... hopefully you don't think less of your FJ. Take it to a dealer ASAP and get the issue corrected and complain like crazy.
Just to chime in: I have well-developed cracks, and have *never* had a serious full-compression incident (although I am carrying lots of added weight, as is listed in my sig). I'm also still under 10k miles.
So you never drove out of an alley, down a driveway, onto a road where the front suspension contacted the rubber bump stops??
If somebody asked me that question, I wouldn't know the answer. Makes me want to have a sensor on the rubber bump stops. And some strain gages on the inner fenders in the rips/bulges area.
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