Metallic rattle from PDK gearbox under low load acceleration?
10-12-2014, 02:11 PM
#1
Metallic rattle from PDK gearbox under low load acceleration?
Hi all
Does anyone notice a metallic clunk/rattle when accelerating at light partial load? I notice it most when up shifting 1-2 around 1-2k rpm. It sounds like it's coming from the gearbox or transmission.
Sometimes if the revs hold constant at that level of load/throttle, a continuous metallic rattle can be heard until revs rise out of that low speed/low load range.
Difficult to describe but a metallic clunk followed by a metallic rattle that sounds like a bag of nuts and bolts rattling around underneath the car.
Likewise when decelerating and downshifting 2-1 there is a slight clunk but no rattle.
I've noticed this noise since I've had the car from new but it seems to be getting louder (or could be my imagination, but like water torture eventually wears you down!)
Under heavier load/acceleration all seems fine, but impractical to bolt off all the time so it is most noticeable in slow moving stop/start traffic.
Wondering if this is normal for PDK transmission, as I didn't seem to notice it on my old 991 C2S but that didn't have AWD
Does anyone notice a metallic clunk/rattle when accelerating at light partial load? I notice it most when up shifting 1-2 around 1-2k rpm. It sounds like it's coming from the gearbox or transmission.
Sometimes if the revs hold constant at that level of load/throttle, a continuous metallic rattle can be heard until revs rise out of that low speed/low load range.
Difficult to describe but a metallic clunk followed by a metallic rattle that sounds like a bag of nuts and bolts rattling around underneath the car.
Likewise when decelerating and downshifting 2-1 there is a slight clunk but no rattle.
I've noticed this noise since I've had the car from new but it seems to be getting louder (or could be my imagination, but like water torture eventually wears you down!)
Under heavier load/acceleration all seems fine, but impractical to bolt off all the time so it is most noticeable in slow moving stop/start traffic.
Wondering if this is normal for PDK transmission, as I didn't seem to notice it on my old 991 C2S but that didn't have AWD
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Juan_Hidalgo (06-04-2021)
10-12-2014, 04:40 PM
#2
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Remember,the PDK is a manual transmission with two clutches. Manuals make noise,as my 991 TS does.This is normal,unless it is real loud or the trans does not shift properly....Don,t sweat it....
10-12-2014, 05:40 PM
#3
I've had more than my fair share of rattles but all have been from interior trim or the sunroof. If there had been a rattle like you are describing fygt I would be nipping down to my nearest Porsche Center to get them to check it out. I'm sure if mine made this kind of noise I would have noticed.
10-12-2014, 07:01 PM
#4
I've found a video of the same noise on YouTube, which this guy has been told is apparently normal. It's a bit faint given the loud background noise level but you can hear the metallic noise from about 3 seconds in. In reality it is probably a bit more prominent, in addition to the gear change clacking. I guess my question is whether this noise is common in your experience? A friend sat in the car and even asked 'wtf is that noise?' 
Had an annoying passenger door rattle appear recently so was thinking of taking it in to have looked at... My park assist PCM screen also seems to show a Carrera from the top down view rather than a Turbo, which I thought was odd...
A friend sat in the car and even asked 'wtf is that noise?' Had an annoying passenger door rattle appear recently so was thinking of taking it in to have looked at... My park assist PCM screen also seems to show a Carrera from the top down view rather than a Turbo, which I thought was odd...
10-12-2014, 07:11 PM
#5
I've never noticed whether the car in the PCM screen is a Carrera but now you mention it I suspect it might be. I'll check tomorrow if I get chance. I suspect it may well be some lazy PCM programmers using a standard graphic!
I'm pretty certain I don't get that noise, the only "current" noise I still have is an intermittent rattle a little bit like the one in the video but more plasticky and from the center console area when driving on rough tarmac.
I'm pretty certain I don't get that noise, the only "current" noise I still have is an intermittent rattle a little bit like the one in the video but more plasticky and from the center console area when driving on rough tarmac.
10-13-2014, 02:20 AM
#6
It appears in this box there are two separate clutch pack/units each comprising 5 friction disc plates each sandwiched between mating steel discs. When the pack engages the plates all pull together and create drive. Disengaged, these 5 (spinning) friction discs would all float freely against the mating metal discs, making contact against one another here and there, so there is an environment for a degree of rattling and rubbing inside the clutch pack (from the friction plates spinning and bumping up against the mating plates). It may be the case that one of these clutch packs has excess movement (between the internal discs) causing a louder rattling and more scraping on contact than usual whilst disengaged. The friction discs are oil bathed so by rights the oil should help alleviate any noise during disengagement due to the lubrication properties of the oil taking up a film between the discs and providing lubrication against the steel rings.
I can say my clutch packs are both very quiet during operation (thankfully). That said there has been the odd day I have heard a very faint tinkle combined with a faint metallic rubbing sound during the warm up phase. Looking at the workings of the packs I think this is to be expected until the oil and all the discs reach operating temperature. There would also be an expansion rate which would tighten up the clearances between the plates and rings seen during disengagement. But I guess if they are still making noise once at temp then again I would suspect perhaps one of the packs has just that little bit too much clearance between the plates during disengagement. In so far a the noises you are experiencing I would say it ultimately comes down to what Porsche considers acceptable, which of course may not be along the same lines as say what you or I may accept. They would probably err on saying if the unit is functioning then all is fine/acceptable. Another thing is these packs appear to be sealed units and it's not as if they can drop the box and take the packs out and apart to see what the clearances are between the friction discs and steel rings and check if they are within spec. I imagine there would be a tolerance and maybe yours are on the higher side = more movement during disengagement. Anything is possible but there is a reason and an answer for everything.
The clunking could well be a bi product of the excess movement between the friction discs not allowing a smooth engagement as say one with less movement.
I can say my clutch packs are both very quiet during operation (thankfully). That said there has been the odd day I have heard a very faint tinkle combined with a faint metallic rubbing sound during the warm up phase. Looking at the workings of the packs I think this is to be expected until the oil and all the discs reach operating temperature. There would also be an expansion rate which would tighten up the clearances between the plates and rings seen during disengagement. But I guess if they are still making noise once at temp then again I would suspect perhaps one of the packs has just that little bit too much clearance between the plates during disengagement. In so far a the noises you are experiencing I would say it ultimately comes down to what Porsche considers acceptable, which of course may not be along the same lines as say what you or I may accept. They would probably err on saying if the unit is functioning then all is fine/acceptable. Another thing is these packs appear to be sealed units and it's not as if they can drop the box and take the packs out and apart to see what the clearances are between the friction discs and steel rings and check if they are within spec. I imagine there would be a tolerance and maybe yours are on the higher side = more movement during disengagement. Anything is possible but there is a reason and an answer for everything.
The clunking could well be a bi product of the excess movement between the friction discs not allowing a smooth engagement as say one with less movement.
Last edited by speed21; 10-13-2014 at 10:33 PM.
10-13-2014, 04:48 AM
#7
I double checked for noise this morning. I too get some start up from cold noises from time to time as speed21 mentioned but I don't find this unusual on a performance car. I don't get any detectable transmission noises at low RPM.
My PCM screen shows a side of view of a Turbo S on startup but the parking screen is a top down Carrera.
My PCM screen shows a side of view of a Turbo S on startup but the parking screen is a top down Carrera.
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10-13-2014, 07:59 PM
#8
Thanks for the detailed explanation speed21 - that makes sense how you describe the noise might come about.
It doesn't seem to happen all the time, so could well be very temperature dependent. It was barely noticeable today if at all, although quite distinct when I was driving the day before. I will keep an eye/ear on the issue if it worsens...
DragonRR - I have the same... only the park assist shows a top down Carrera. Lazy programmers!
It doesn't seem to happen all the time, so could well be very temperature dependent. It was barely noticeable today if at all, although quite distinct when I was driving the day before. I will keep an eye/ear on the issue if it worsens...
DragonRR - I have the same... only the park assist shows a top down Carrera. Lazy programmers!
10-13-2014, 10:25 PM
#9
Porsche use the ZF box. Check this link out for a better understanding
http://www.zf.com/corporate/en/produ...smission.shtml
Ensure to click on the video to see a detailed operation of the g/box and dual wet clutch packs. The activation is electric hydro mechanical, not magnetic as previously thought. The internal 5 pack of friction plates which spin sandwiched between the other mating pack of plates obviously must come into some form of contact with one another during disengagement, so there is an environment for a degree of rattling and rubbing (metallic) scaping noise to occur as these 5 plates make intermittent contact with their mating running surfaces, I assume mainly due to the vibrations transmitted from the engine. I imagine the more clearance which exists between these running surfaces during disengagement the more likely the environment becomes for rattling/scraping to occur. Obviously there is oil present from the oil bath which should alleviate direct contact with the surfaces (and subsequent noise) but again I suspect that is governed by clearances between these running surfaces and, the level of engine vibrations transmitted into each of the 2 separate clutch packs.
In sports mode, as the engine mounts become solid, the environment for vibrations to be transmitted into the packs increases. Maybe when the engine/box is cold perhaps try using it in normal mode to see if the rattling is reduced at all? Once the packs have reached normal operating temps by rights the rattling should reduce due to general expansion of the plates and lubrication, so sports mode may not be any different than the normal mode at that stage.
http://www.zf.com/corporate/en/produ...smission.shtml
Ensure to click on the video to see a detailed operation of the g/box and dual wet clutch packs. The activation is electric hydro mechanical, not magnetic as previously thought. The internal 5 pack of friction plates which spin sandwiched between the other mating pack of plates obviously must come into some form of contact with one another during disengagement, so there is an environment for a degree of rattling and rubbing (metallic) scaping noise to occur as these 5 plates make intermittent contact with their mating running surfaces, I assume mainly due to the vibrations transmitted from the engine. I imagine the more clearance which exists between these running surfaces during disengagement the more likely the environment becomes for rattling/scraping to occur. Obviously there is oil present from the oil bath which should alleviate direct contact with the surfaces (and subsequent noise) but again I suspect that is governed by clearances between these running surfaces and, the level of engine vibrations transmitted into each of the 2 separate clutch packs.
In sports mode, as the engine mounts become solid, the environment for vibrations to be transmitted into the packs increases. Maybe when the engine/box is cold perhaps try using it in normal mode to see if the rattling is reduced at all? Once the packs have reached normal operating temps by rights the rattling should reduce due to general expansion of the plates and lubrication, so sports mode may not be any different than the normal mode at that stage.
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HankB (09-25-2019)
04-30-2020, 05:24 AM
#13
Advanced
I have a 2014 991 turbo. I have a small rattle should inside the cabin at idle. At first we thought the rattle noise may be coming from the rear pully tentioner, but you can only hear the rattle inside the cabin. You can not hear any unusual noise while standing outside at the rear of the car. It is hard to describe the noise , it come and goes and its not very loud, but you can hear it if you try to notice. it is like a rotating pully or disk metal rubbing, swooshing sound. Goes in and out.. I think when car is cold it sounds more.. Im not sure yet.
On scale of 10 being very loud, its at about a 1 - 2 while at idle.
When stopped at a traffic light. nothing major but a small rattle. I spoke to a porsche tech and he said it seams to be coming form the center bottom area (PDK area) . This can be the same thing like you mention. Im going to have the PDK oil replaced to see if this helps get rid of some rattle noise. Any suggestions on pin pointing the issue would be helpful. Thank you
On scale of 10 being very loud, its at about a 1 - 2 while at idle.
When stopped at a traffic light. nothing major but a small rattle. I spoke to a porsche tech and he said it seams to be coming form the center bottom area (PDK area) . This can be the same thing like you mention. Im going to have the PDK oil replaced to see if this helps get rid of some rattle noise. Any suggestions on pin pointing the issue would be helpful. Thank you
04-30-2020, 12:29 PM
#14
Rennlist Member
yes I thought is was a slight noise form the rear pullys.. in fact previous owner had the pully tentioner replaced by the dealer at 24k miles.. car has 28k now. So thats why I thought pullys.. there is still a small sound in the cabin. My current porsche specialist says small noise is from PDK clutch plates under car not the back. They ae doing a PDK oil replacement. Let's see what happens with the small grinding/noise. I'll keep you posted.
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lolo2102 (05-01-2020)
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lolo2102 (05-02-2020)