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All that the vibration damper does is limit the noise and vibration of the pipe enclosing the shaft. It doesn’t do anything to the shaft. The carrier bearings are super important to how the driveline functions, the vibration dampener is not. It’s a NVH sort of an issue only.
That said, if there’s any NVH coming from the tube that I don’t like, the thing will go back in - provided the new rubber is available.
All that the vibration damper does is limit the noise and vibration of the pipe enclosing the shaft. It doesn’t do anything to the shaft. The carrier bearings are super important to how the driveline functions, the vibration dampener is not. It’s a NVH sort of an issue only.
Agreed. The donuts also keep the damper from sliding back and forth under acceleration and braking, which you will be doing in abundance. As long as you have to push the damper in and it stays in place, cool.
The vibration dampener will dampen the vibrations on the shelf:
Come on....you guys are smarter that that!
All the frequencies that the damper normal absorbs are going to be directly transferred to the transmission. The harmonics will quickly destroy the transmission, given the load and speeds you are using.
You think that Porsche tested every single torque tube, measured the frequency, and installed the exact proper weight in the exact proper position because they just wanted to add weight?
Look at the rubbers on the damper from every torque tube. They are always completely pounded and worn out long before the bearing carrier rubbers do. The bearing carriers can not possibly absorb frequencies, they are hooked to both the shaft and the torque tube! They can only transfer the frequency "wave"! Only the damper can absorb, through the rubbers (the frequency "wave" is turned into heat, though the rubbers, which is why they always are much worse looking that the bearing carriers.)
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
My thinking is that the torque tube damper is a tuned mass damper that is tuned to a relatively narrow frequency. My understanding is that it’s used in cars to quiet the cabin. In the case of 928, I believe the torque tube housing would resonate with some gear noises etc. and that’s why the models targeting audiences that sometimes want a quiet cruise mode have those. If this is not the case, someone educate me.
Now, I’m all for a quiet cruise. But with super bearings and all the other changes I’m not sure how effective the damper would be. So I’m trying my luck first without it and if the tube is noisy then I have to measure the frequency and figure out the solution. One solution may be, should a noise problem arise, a select 928 original damper with the 929intl new rubber.
It’s my understanding that literally everything impacts the resonant frequency. The weight of the bearings, stiffness of the rubber isolators on the bearings, locations of the bearings, etc. To reduce torque tube noise, it’s either a fairly complicated engineering calculation or trial and error.
By the way, what do the markings on these vibration dampers mean? The Hertz number is the (anti) resonant frequency, I assume. Does the degrees number refer to the factory installation tool that determines the exact installation location? I’m speculating, no knowledge implied by pointed questions.
My thinking is that the torque tube damper is a tuned mass damper that is tuned to a relatively narrow frequency. My understanding is that it’s used in cars to quiet the cabin. In the case of 928, I believe the torque tube housing would resonate with some gear noises etc. and that’s why the models targeting audiences that sometimes want a quiet cruise mode have those. If this is not the case, someone educate me.
Now, I’m all for a quiet cruise. But with super bearings and all the other changes I’m not sure how effective the damper would be. So I’m trying my luck first without it and if the tube is noisy then I have to measure the frequency and figure out the solution. One solution may be, should a noise problem arise, a select 928 original damper with the 929intl new rubber.
It’s my understanding that literally everything impacts the resonant frequency. The weight of the bearings, stiffness of the rubber isolators on the bearings, locations of the bearings, etc. To reduce torque tube noise, it’s either a fairly complicated engineering calculation or trial and error.
By the way, what do the markings on these vibration dampers mean? The Hertz number is the (anti) resonant frequency, I assume. Does the degrees number refer to the factory installation tool that determines the exact installation location? I’m speculating, no knowledge implied by pointed questions.
If it was only a noise issue, I'd be tossing these things out, too.
The problem is a vibration issue, from the torque tube shaft turning into a sine wave.
People "get away" with putting 3 bearings in the automatic torque tube and leaving the frequency absorber out....because they do not use their cars like Porsche tested them. Most of these cars are now "cruisers". Almost anything works in cruiser mode.
You, however, seems like you are interesting in running your car very hard.
There's a good reason that automatic torque tubes only have two bearings...and there's that heavy lump of cast iron suspended in the rear of the torque tube.
If it was only a noise issue, I'd be tossing these things out, too.
The problem is a vibration issue, from the torque tube shaft turning into a sine wave.
People "get away" with putting 3 bearings in the automatic torque tube and leaving the frequency absorber out....because they do not use their cars like Porsche tested them. Most of these cars are now "cruisers". Almost anything works in cruiser mode.
You, however, seems like you are interesting in running your car very hard.
There's a good reason that automatic torque tubes only have two bearings...and there's that heavy lump of cast iron suspended in the rear of the torque tube.
Thanks for the response! I’ve got many disadvantages in this hobby car effort but one of them is not that I already know everything! . Let me think this all thru and see if I can explain my (possibly revised) views after that.
Thanks for the response! I’ve got many disadvantages in this hobby car effort but one of them is not that I already know everything! . Let me think this all thru and see if I can explain my (possibly revised) views after that.
Things can be really tough to figure out, without firsthand knowledge from the engineers that designed this stuff. In this case, we are left with some "solid" clues, which help.
I find my self always asking: "Why did Porsche do this, in the first place"? (Every single piece that gets added, when Porsche builds a car, adds weight and cost to that vehicle.)
There's several clues in Mark Anderson's picture of dampers, above.
The most obvious: Looking at the different numbers written on each damper, it is pretty evident that every damper has a different frequency written on it....and what appears to be a different angle.
Think about trying to dampen a resonant wave at a particular frequency. The particular resonant frequency and point of excitation would determine where (how far from...) the excitation point you'd want to place the damper. The damper itself would need to be "big enough" and have its own resonant frequency not harmonically related to the tube's.
Prior to installation of the shaft, one would want to suspend the tube vertically and ring it. The largest amplitude node point is where the damper needs to sit in the tube.
Things can be really tough to figure out, without firsthand knowledge from the engineers that designed this stuff. In this case, we are left with some "solid" clues, which help.
I find my self always asking: "Why did Porsche do this, in the first place"? (Every single piece that gets added, when Porsche builds a car, adds weight and cost to that vehicle.)
There's several clues in Mark Anderson's picture of dampers, above.
The most obvious: Looking at the different numbers written on each damper, it is pretty evident that every damper has a different frequency written on it....and what appears to be a different angle.
What logical reason/reasons fit this one clue?
I believe that the Hz value corresponds to tested anti-resonant frequency for the damper, measured on a test jig. I don't know what the degree value is, any ideas? Molding the rubber and casting the weight are not precision operations, components come out with different anti-resonant frequencies. So that's why there's a damper specific measurement value.
I believe that Porsche measured a torque tube housing and cabin resonance at 70Hz for five speed cars and 55Hz for automatics. I believe (but don't know) that they then installed the dampers with relatively low values from those at hand to automatics and those with relatively high values to manual cars. Although this type of damper is a tuned narrow-band damper, it does dampen a range of frequencies around the measured value.
I believe that this tube housing and cabin resonance is very different from the driveshaft resonance. Drive shaft resonance is what has the potential to break components. The way they eliminated the drive shaft resonance was by specifying those carrier bearings. More carrier bearings => shorter segment lengths => higher resonant frequency. Also, larger shaft diameter => higher resonant frequency. The resonant frequency of the driveshaft as installed with bearings was made high enough that the engine can't excite it either at frequency equal to engine rpm. [Edit: 4*engine rpm, i.e., firing frequency can be met for below redline rpms.]
I believe that the rubber spring wears on that tuned vibration damper from forward-backward movement as the car accelerates and brakes. The bearings weigh less and they also hang on to the driveshaft, so the rubber bearing isolators don't wear in the same way from forward-backward motion.
Ok... Think about trying to dampen a resonant wave at a particular frequency. The particular resonant frequency and point of excitation would determine where (how far from...) the excitation point you'd want to place the damper. The damper itself would need to be "big enough" and have its own resonant frequency not harmonically related to the tube's. Prior to installation of the shaft, one would want to suspend the tube vertically and ring it. The largest amplitude node point is where the damper needs to sit in the tube.
Tuned vibration damper is indeed most effective if placed in the largest amplitude vibration point.
However, I think in this case, the relevant setting is the torque tube installed as the engine-tube-transmission combination is what we're trying to dampen here. Just hitting a loose tube with a mullet may get you the wrong answer.
Porsche helpfully documented that resonant value being being 70Hz for five speed cars and 55Hz for automatics. We can probably infer something about the largest amplitude vibration point from where they chose to place the damper.
06-13-2019, 03:08 PM
. Let me think this all thru and see if I can explain my (possibly revised) views after that.
