Sonics

I have no idea if it’s normal, but when my car is back from the dealer I can check to see if mine is similar.

I assume you had to remove the wheel to do that check?

Mootz

No, just turn the wheels all the way to one side and you can reach right in. I know some movement parallel to the axle--in and out of the differential if you will--is normal, but this movement is side to side, up and down.

I also noticed right around the same time the vibration began, when performing a launch, I started hearing a thump on engagement as if a transmission mount or some other mount was loose/broken. I reported this to the dealership but they said was everything looks normal. I you are willing to try a launch, I'm curious if you notice the same. The car never did this before the vibration began.

Sonics

Well that’s easy then, I’ll definitely post a similar video once the car is back.

I have done a handful of launch controls and not noticed a thump, however the whole process is so violent that I could well be missing it. I’ll try a few and pay attention for any untoward thumps or similar.

djdonte

Thumping on launch is a telltale sign it’s the rear suspension. Up until this car I’ve almost exclusively drove RWD muscle cars, and we call it wheel hop or axle tramp. The rear suspension squats when you accelerate, even more so on a lanch. It gets worse the more power you make and for older cars there is a slew of fixes. In fact (not sure on Ford) but GM started using asymmetrical cv axles to combat the problem. Just my two cents.

Sonics

I got my Panamera 4 E-Hybrid back from the dealership where they were working on several unrelated issues.

I have not yet had a chance to manually inspect the axel play or do a launch control, but I have done a good bit more vibrational testing while driving and the results are interesting. I will preface these results by saying that as soon as I got the car back, I took it to the same reputable wheel shop and they checked the two front wheels they previously straightened free of charge and both were good. They also checked the two rears and found and corrected a very slight bend on one of them. They also checked the balanced on all four wheels. This made basically no discernible difference at all in the car's behavior, so my comments below apply to both before and after this latest work.

On my car with 21" wheels, the tire circumference is about 89.5" which means they revolve about 708 times per mile. That means that for each 1mph of speed, they are turning about 0.19665 Hz. We can use this number to find the T1, or tire rotation frequency, for any speed. At 57mph, which is where members generally report that the vibration starts and is near its worst, the T1 is about 11.2 Hz. Given that the speedometer on our cars is about 2 mph optimistic, the actual T1 at 57mph indicated may be slightly lower, perhaps 10.8 Hz.

Here is an FFT 3-axis acceleration spectrum taken while driving in a straight line at approximately 60mph.

Figure 1 (60mph) (PASM Normal, Ride Height Normal)


The bright line around 11 Hz in Figure 1 corresponds to the approximate T1 frequency and is the predominate component of the vibrational spectrum, although it does appear as though its milder second harmonic is visible around 22 Hz. This behavior at 11 Hz is exactly what we would expect if a single out of round wheel, bad CV joint, bent axel, or anything else that rotates at the same speed as the wheels is causing the vibration.

Here is another acceleration spectrum of the car driving at 30mph.

Figure 2 (30mph) (PASM Normal, Ride Height Normal)


Note that there is still significant energy displayed around the 11 Hz range, although the spectral line is not nearly as defined as in Figure 1. This is notable because the T1 frequency at this speed would be approximately 5.5 Hz, but that is not visible on the graph. Despite the lack of measurable T1 energy, the same 11 Hz range is resonating at this speed. This is concurrent with members reports of vibration around 30mph.

Here is another acceleration spectrum of the car driving at 75mph.

Figure 3 (75mph) (PASM Normal, Ride Height Normal)


At 75mph the T1 frequency is approximately 14.9 Hz and a bright spectral line is visible around that frequency on the graph, likely indicating that on my car there is a wheel or other T1 component that is not perfectly round or balanced. However, it is very notable that there is still significant energy around the 11 Hz range, just like in Figure 1 and 2. Unlike in those figures, there is no harmonic relationship between 14.9 Hz and 11 Hz. This may indicate that the car is resonating around 11 Hz regardless of frequency input around that frequency, at least as long as there is sufficient broadband excitation to induce the resonance, such as from the road surface.

It seems to me from this collection of measurements that one single issue is not responsible for the vibration issues in these vehicles. If it was a simple T1 vibration as previously posited, the T1 spectral line would predominate and change directly with speed and the 11 Hz range would not be present at various speeds. There seem to be two interrelated factors here: an excitable resonance around 11 Hz and a T1 vibration which may excite the former, especially when they are close to equal or a harmonic of each other, such as around 60 mph.

These measurements of the car displaying significant resonance around 11 Hz across a wide range of speeds may indicate that something in the car's body, suspension, or mounting systems has a natural resonant frequency around that range. It would also explain why members have reported having all of their wheels and tires replaced but the issue remains. If something in the vehicle can become excited and resonate at those frequencies, it does not necessarily require a T1 vibration to induce. This theory also potentially explains why some members find the vibration to be so inexplicably variable with no particular patterns - if an out-of-round wheel or other T1 problem is not causing the issue - the excitation of the resonance will depend on much more unpredictable factors such as the pattern of the road surface and bumps delivering potentially excitational energy.

While members could have any number of reasons for an exacerbatory T1 vibration such as any out of round wheel, axel, or other component, members' descriptions of the shaking are remarkably consistent. Further, the speeds at which almost all members describe the vibration as being worst - 57mph to 65mph - correspond very neatly to the frequencies at which even the most minor T1 vibration could excite our suspect 11 Hz resonance. Members who have had all wheels and tires replaced to ensure that they are perfect still experience this problem, which is consistent with a resonance that is not solvable by eliminating T1 vibrations as it can still be excited by the road surface. This is also confluent with members' reports of PCNA describing the problem as a "normal" "harmonic characteristic" of the vehicle, although this does not explain why most, but not all, Panameras seem to only behave this way after some aging.

The most immediate suspect in a vehicular resonance is naturally the suspension. However there are some problems with this theory with respect to the available data and members' reports. Most loaded car suspensions systems have a natural resonant frequency of about 1 Hz to 3 Hz, which is an order of magnitude lower than what has been measured around 11 Hz. Also, members generally report little to no difference when changing suspension settings, including ride height and damping. With credit to savagegeese's superb Youtube video "Porsche Panamera | Future of Cars", the Panamera has an exceptionally wide range of spring rate adjustability from the three-chamber air suspension design.

Figure 4

A little back-of-the-napkin math indicates that with even weight distribution between the four corners of the car, the natural frequency of the suspension is about 0.8 to 1.3 Hz with these spring rates. This is far outside the 11 Hz range in which we have the resonance. It is also very important to note that if the air springs were the culprit, the resonant frequency of the problem would change substantially in response to changing their changed spring rate. I investigated this by taking a measurement at 75mph in Sport Plus.

Figure 5 (75mph) (PASM Sport Plus, Ride Height Normal)

Figure 5 does not show significantly different behavior from the 75mph measurement in Figure 2. There is the T1 line around 15 Hz and the suspect resonant content around 11 Hz, notably unchanged by the variation in suspension spring rate and thus suspension natural resonant frequency.

While members may have varied reasons to suffer a T1 vibration, likely most commonly an out-of-round wheel, we must identify the cause for the car's tendency to resonate around 11 Hz which I believe is the culprit for the problems reported in this thread. From my analysis above, I do not believe the problem to be with the main air springs. I am very curious if any members have had any suspension components replaced and to what effect.

In researching the 971 suspension system, I noted that it has "hydro-bearings on subframe and transverse links" (pdf link). Such fluid-filled bushings are notorious for leaking and losing their desired damping properties over time. I am starting to wonder if some such parts that couple the subframe with the suspension to the body of the car could be responsible for the 11 Hz resonance if they lose their desired properties over time. All of the front and rear control arm bushings are called out in parts descriptions as being "hydraulic mount" (971-505-544, 971-407-183-D, 971-407-183-C). The front (971-505-541-A) and rear (971-505-543-C) "isolator" bushings are not called out as being hydraulic, but I suspect they might be fluid-filled and are possible culprits for the 11 Hz behavior.

I am very interested to hear other members' thoughts on possible causes for the 11 Hz behavior that I have documented above. I will be having my dealer replace all four wheels and tires in a trial to see if it fixes the vibration, but I might not have the opportunity to take measurements during that test. Given everything above, however, I do not believe that it will fix the problem. I will ask the dealer to inspect all of the suspension and subframe bushings, although I have no concept of if they can be diagnosed without presumably costly removal and replacement.

Norge911

Great write up.
would you be able to check vibration around 82-84mph as well, I know over legal speed limits but some have reported vibration in this range too.

I am unsure about the parts you listed. They have 971 part number but are used on other VW group cars and those cars have not reported same vibration. The parts you list in combination with axle distance and weight would have an impact as well so could be unique to the Panamera as other VW cars would be slightly different.
in my car I have minor vibration around 27mph, high amplification around 57-62mph. I also have vibration at 83mph but appear as lower amplification and shorter period. At 83, I can feel more of the vibration in the steering wheel as well.
another uniqueness, braking from 45-50mph is smooth, at 70mph it is smooth. However, when I start braking from 65-57mph, I can feel pulsation through the pedal. Also, it appear that if I leave car in high overnight vs low and make a drive in normal ride night after and checking for vibration, there is more vibration after leaving in high.
Therefore, I think the problem in my car is something rotating and after front diff. and inside of wheels and brake rotor. Maybe CV join on intermediate axle or a bearing on front axle or hub.

I agree, does not appear to be dynamic engine mounts or suspension as motion is present at same intensity and Hz in sport and sport plus settings. Hz would move/shift if those components were cause as you changed stiffness.

Norge911

Have you also tried to move phone/ sensor around car, if front left vs right and trunk to see if there is a change?
maybe you could isolate the vibration further?

Sonics

@Norge911 , thank you for your detailed response and descriptions. I will try a higher speed measurement, although it will require the right time and place since I need to maintain that speed constantly for some time for a good measurement.


My understanding is that our cars do not have active engine mounts. However I am less inclined to suspect the engine mounts since in my E-Hybrid the behavior is completely invariant of whether the ICE engine is on. Also forum members have reported similar behavior with both V6 and V8 engines which have different weights and should behave at least somewhat differently on their mounts.


I don’t doubt that you may very well have an issue that is causing a T1 vibration in your vehicle, it sounds as though in your case it could possibly involve the braking system. However, I believe that your vehicle, like mine, suffers from an unexplained resonance that stores and amplifies that energy resulting in the highly speed-dependent symptoms that have been extensively described in this thread.

I have not tried moving the phone to different locations. All measurements are with it flat on the center armrest. The application I use is not well suited to detect absolute differences, the graphs are most useful in a qualitative sense to see the relative spectral content, rather than to see specific amplitudes. I further suspect that the body of the car is sufficiently rigid to transmit the vibrations throughout the whole vehicle.

If you are inclined to take measurements of your vehicle I would be very interested to see and analyze them. The application I use is intended for physics eduction and is free, it is called phyphox and available for iOS and Android. I use the "Acceleration Spectrum" tool. If you do take measurements, I would be very interested to see at least a measurement around 57-62 mph and another at significantly higher speeds, such as 75mph up to your additional problem speed of 83mph. For the best results you should have the car on cruise control and a relatively smooth road surface. I simply take a screenshot of the results under "history" when I have a good run.

Ericson38

None of these reports are for 2wd cars. I think I'm the only 2wd model posting in this thread, and I don't have any vibration at all at any speed (2019 Base owned from one year old and 2K miles till now at 14K miles).

Sonics

Do you have PASM with air suspension?

I am starting to suspect the latter is associated with the real culprit, not necessarily the AWD system. My supposition is that few 2WD cars were optioned with PASM and air suspension.

Ericson38

All 971s came with PASM, so we have that, and no air. I could not see needing air with this car in any sense. I tend to like stiffer suspension, like our 997 has, which I like to commute to work in except for the winter months. I operate her 971.1 with PASM in max firm mode about 50% of the time. But never in the softest mode.

Sonics

Thank you for the clarification, I did not realize that the steel-spring 971s came with PASM. I'm glad to hear that you have not suffered any of these mysterious shaking problems!

NoSoup4U!

I wonder if this issue affects all Panameras, the sedan as well as the Turismo? It probably does but with an issue as obscure as this one, it could be worth having another data point.
Being soon in the market for a Sport Turismo, this issue could give one pause.

Ericson38

Not normal, and is probably the same issue that the Turbo had in this thread (front axle 1/2 shaft drive bearing wear excessive in diff housing). The cardan shaft spline inserts into this coupling, which is held in alignment in the front drive housing by the bearing they change in the referenced thread. Changing the cardan shaft is not the solution.

Turbo Left front drive axle stub loose- Service parts available? - Rennlist - Porsche Discussion Forums

Sonics

I checked my front left and right. There is no up/down or side-to-side play at all. On the left there is maybe 1-2mm of in-out play. On the right there is no in-out play.