I'm no shock/strut design engineer but reading through this thread and others about suspension clunks on radflo setups recently makes me think the noise is coming from the inside the shock when it goes from compressed to full droop rather quickly (like over a speed bump at any significant speed). In this scenario, the fluid has to move from one side of the piston through the orifices to the other real fast and when that happens if the shock internals aren't correctly designed you'll hear a clunk, either from component contact or more likely the clunk is really a hydraulic lock sound that occurs when the shock is trying to push more fluid through the orifice than can fit in that amount of time.... once again, no expert or design engineer here, just my guess the clunk will never go away until you replace the bilstein shock something like an icon that doesn't exhibit this clunking behavior supposedly.
maybe [MENTION=66316]1engineer[/MENTION] can give a better technical hypothesis on this topic.
If this is indeed the case, it's sad Toyota overlooked this in it's suspension component selection for the TRDP. Then again, it's also said they missed the rubbing issue on the front fender. I mean, did they even test drive this thing before production?! If they did even for 5 minutes they would have surely experienced both these conditions and realized it's not acceptable for production on a 45K SUV.
There have been several threads on suspension clunks ranging from only TE's with KDSS to all 4Runners making a slow left turn. Now this thread on the TRD Pros.
I have refrained from getting involved in these threads (except in the KDSS one because they were going down the way wrong path) and truthfully I really do not know why people have clunking suspensions.
In some threads they say it only happens when it's cold. In other clunk threads it's only one model of 4Runner. Still other threads list only specific instances (ie speed bumps, left turns, etc) when they hear the clunk.
Here is what I DO know:
It IS NOT the hydraulic fluid in either the KDSS system or conventional suspension shocks. While Nate's idea has merit, hydraulic fluid will either hiss, whine or groan when subjected to unusual operating parameters. Not clank or clunk.
If the noise is a muted "CLUNK," it quite often is coming from a bushing or a component isolated with bushings because the bushing is dampening the sharp "CLANK!" sound that comes from metal hitting metal. A worn out shock is a good example of a component that makes a clunk because it is isolated with bushings.
If I were you guys who have this noise and you really want to solve this issue you must do some of the leg work yourself. Taking something like this to a mechanic without having a specific idea and location of the issue is iffy at best. They are not going to put in the time necessary to troubleshoot it if it is a random and part time noise. After reading about the many trips to the dealer and having the issue unresolved tells you something different needs to be done if you want to get it fixed.
The idea of mounting a GoPro under there is a good one but you still have to know some other things. For example, if the noise only happens when it's 30 degrees or colder then that weights the issue towards something that is influenced by temperature.
I would:
Take an hour or so to run some tests like
1. Slow abrupt left and right turns.
2. Hitting speed bumps perpendicular and angular.
3. Pothole tests.
4. Reverse turn tests.
5. Hard braking tests.
Try these tests in certain conditions, like cold, dry, wet, hot, etc, and DOCUMENT the conditions of the test!
Once you have identified which maneuver and condition required to make a repeatable noise THEN you can mount a GoPro under there (multiple tests with camera/mic mounted in different locations to triangulate the noise) and see if you can identify which component/bushing/joint is actually clunking.
After you do this then you can go to the dealer with confidence and point to a specific component/bushing/joint and tell them "Hey. This makes a clunk when I do "X" in "Y" conditions. Replace it! They will do so without fail and this should solve your problems.
I know this is not what you guys want to hear but difficult problems usually require a lot of time to solve for the solution. I'm pretty sure once somebody does the outlined process above there will finally be a solution. Until then, there will just be more threads on this subject with no resolution. Good luck and I will be happy to advise.
