Jasonharper
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Some information from Volkswagen explaining auto hold and brake pressure https://www.volkswagen.co.uk/technology/driver-assist/braking
Growing vibration while in D or R (S-Tronic)
- Thread starter Mr Olympik
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Jasonharper
New Member
Some information from Volkswagen explaining auto hold and brake pressure https://www.volkswagen.co.uk/technology/driver-assist/braking
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I find it difficult to understand what is the difference between you pressing the brakes harder without Auto Hold and Auto Hold keeping the pressure for you? It should be the same (with vibrations) either way.
My understanding is that as the clutch is linked to the brake, the pressure of the brake pedal engages and disengages the clutch. Auto hold may keep the clutch lightly engaged to prevent roll back on hills.
Need a mechanic to confirm.
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Need a mechanic to confirm.
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What I have read about the Auto Hold is that it remembers the brake pressure and uses the ABS central to keep the pressure in the system simulating that you are holding the brakes. If the clutch operation is linked to the brake pedal applied/released then it is huge disadvantage to use the Auto Hold as it will worn out the clutches faster and is huge misengineering.
Makes sense what you’re saying.
Purely speculating; the auto hold stops excessive wear and applies the clutch for a smooth uphill start, otherwise you’d be dumping the clutch and banging gears? Clutches are consumable whereas gearboxes aren’t really.
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Purely speculating; the auto hold stops excessive wear and applies the clutch for a smooth uphill start, otherwise you’d be dumping the clutch and banging gears? Clutches are consumable whereas gearboxes aren’t really.
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I think it is balanced, when the clutch is starting to engage then the brakes are released. Keeping the car still with the clutch I've seen on cars with torque converter only. My former Toyota was working like that. But it would be good if there is someone that can enlighten us about it.
Jasonharper
New Member
This vibration when idle at gear engaged is very interesting topic. Not just because I have it in my car, but because I have investigated number of scientific research papers related on dual-clutch transmission operating dynamics. Not yet found possible reason for Stronic vibration, but found some researchers who could be able to explain DCT dynamics for this specific situation. Let see... I might try to get contact with some of these researchers and look if they are willing to discuss about the topic.
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Currently I have no vibrations and I am about to retrofit the Auto Hold so I will be able to tell you if there is a difference before and after the retrofit.
Jasonharper
New Member
This research paper / Master thesis discusses about trańsmission technology vibrations https://pure.tue.nl/ws/files/46847781/584166-1.pdf
Below is the most interesting part. I have noticed in my car when it is running just little over 800rpm idling, vibration starts, but some times when idling is little below 1000 rpm, there is no vibration at all. May be there is a design mistake on DMF springs sizing or idling RPM level parametering...
Below is the most interesting part. I have noticed in my car when it is running just little over 800rpm idling, vibration starts, but some times when idling is little below 1000 rpm, there is no vibration at all. May be there is a design mistake on DMF springs sizing or idling RPM level parametering...
Sortik
New Member
There are users that still have the vibrations after changing the DMF. And the same DMF is used in other cars so if it would be just about DMF I think there would be way more users but I would still try to change it. I would choose SACHS instead of Luke because Luke is OEM part and if it has any problems maybe SACHS doesn't have it. I just don't get the temperature dependence in this equation. I really must drive on a highway for about one hour when it is cold outside. The engine itself is warmed quite fast but this has to be something else and I think that DMF is warmed up way slower and maybe once it reaches a certain temp it stops vibrating. But as I said it can be a combination of more parts.
The only time when mine doesn't vibrate is when DPF filter regeneration is active but I doubt that it is only due to the raised RPM because mine are permanently raised by 50 rpm and it still vibrates. Maybe the clutch is less engaged during the regeneration (I don't have a VAG cable right now so I can't check it)
The only time when mine doesn't vibrate is when DPF filter regeneration is active but I doubt that it is only due to the raised RPM because mine are permanently raised by 50 rpm and it still vibrates. Maybe the clutch is less engaged during the regeneration (I don't have a VAG cable right now so I can't check it)
Jasonharper
New Member
See my text in other forum. https://www.motor-talk.de/forum/aud...uf-im-stand-t6568432.html?page=7#post61359763 If you change to original Audi DMF, you may get DMF with same design specs which cannot dampen the vibration in low idling rpm's / frequencies.
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Sortik
New Member
I just saw that. I have notifications for that topic. I like your interest in this. You may be on the right track but I still don't think it would be that easy. According to the brake pressure ... also in my case, it stops vibrating when the pedal is just slightly pressed but this doesn't change the RPM. Also, the clutch is still partly engaged when the brake pedal is hard-pressed. You can compare the clutch oil pressure in N with different pedal positions. But different pedal position definitely changes the torque on the DMF and mass which is connected to it. I would really like to change the DMF but spending the money just out of curiosity is not the best idea. I am used to shifting to N while idling which is also beneficial for clutch wear.
I am curious what would be the answer if more users unite and write to Audi about this
Same thing here with the varied brake pedal pressure and vibration.
Regarding a mass action to Audi: nothing would happen, judging from the lack of response and interest on retrofitting google/satellite maps... most dealerships don’t acknowledge the existence of a patch as its a FOC repair and they don’t want to use their workshop time.
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Jasonharper
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This is a short paper also discussing about vibrations and dampening https://www.schaeffler.com/remoteme...sia_1/downloads_11/1_Dual_Mass_Flywheel_1.pdf
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Sortik
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RPM is the same no matter the brake pedal position. Even if I depress the brake fully and the car moves without gas pedal RPM still remains the same
Jasonharper
New Member
My car is getting worse and worse with the vibration issue. It is so bad I needed to get replacement car from used car dealer until it is repaired. Now I hear crackling noise always when driving and pressing throttle. I can hear it best when right front window is open and when driving close to wall on that side. While driving around 1400rpm the transmission generates some kind of bouncing. Also nowadays up and downshifting both comes with one or two bounce. On motorway when releasing throttle on downhill and car goes freely on engine braking mode it gives continuous bouncing from transmission. I am taking the car to Audi center on 6th July for a troubleshooting process (both mechanical and electrical). My guess is the DMF has come to end of life-cycle.
If it is DMF, I am wondering if could be replaced with centrifugal pendulum absorber model:
If it is DMF, I am wondering if could be replaced with centrifugal pendulum absorber model:
Jasonharper
New Member
Latest update. My car got diagnosed today by Audi Center. DMF as well as front right side shaft's both inner and outer joints need to be replaced.
DMF is keeping noise when opening right front window and driving close to wall. In normal drive the noise cannot be recognized in the cabin. They did the diagnosis by lifting the car while engine is running and then listening under the car from where the noise is coming when someone is accelerating the car on the crane.
DMF is keeping noise when opening right front window and driving close to wall. In normal drive the noise cannot be recognized in the cabin. They did the diagnosis by lifting the car while engine is running and then listening under the car from where the noise is coming when someone is accelerating the car on the crane.
Jasonharper
New Member
I am waiting for an approval for the repair from the used car warranty manager (non-Audi company where I bought the car a while ago). Parts and their repair / change are included to used car warranty coverage. Parts are coming from and the repair will be done at the local Audi center (hopefully). I did 3 weeks ago a DMF part query also to a local Audi center. According to them, here in the Nordics there are not even single DMF of this model in the inventory and Audi Germany's inventory shows orange meaning that it may take some time to get it on here. Before confirmed delivery time of DMF, the repair cannot be scheduled.
Jasonharper
New Member
Sortik
New Member
I am happy that your problems are gone. Thanks for letting us know. I think that the noise you heard wasn't from the DMF but from the shaft. I have the same noises and saw this problem also on facebook A4 b9 group. Multiple users reported that this is a common problem. May I ask what kind of DMF did you get? Original Sachs? thanks
Jasonharper
New Member
Yes, you are right. The major noise was from the right shaft, but there was also a noise from the DMF based on what Audi center told me. I do not know the DMF manufacturer, but it is Audi original, thus I think it is Sachs. Even after having these repairs, the car still have some loose in power line which can be recognized during the gear shifts. I think the dual clutch should have been changed also. I did not have anymore time and patience to start a new problem solving and cost negotiating process with Audi goodwill process and used car dealer, so I decided to sell this car. I owned the car for about 8 months and it was under the problem solving process all the time.
