Tranny rattle and vibration issue need advice.

So I am battling a couple of issues with my 99 996 C2. For the record I am a Porsche newb and have only owned this 996 for a few months now. Car has 65K on it. The only change I have made to the car since I purchased it was installing a set of Fister 3.6 modded cans. It would seem unlikely that the new cans are causing the vibration issue. 1) I am starting to notice a engine vibration at around 1000 and then again at about 3400 RPM. It is most noticeable when the car is up to temp vrs when its cold. It was subtle at first but seems to be getting more noticeable. 2) There is a rattle sound coming from what i think is the front of the 6 spd gear box at idle it is not constant but comes and goes every 20 to 30 seconds. I cannot hear it when I rev up the engine as everything seems to get washed out by the fisters. I tried searching the forum but did not come up with anything so I figured I would ask the experts. Thanks, Andy

Does the car have a light weight flywheel? Does the rattle change when the clutch is pushed in? Also check the engine mounts and the trans mount. New engine mounts could make a big difference if the current ones have leaked/gone "flat"

I am not sure about the LW flywheel is there an easy way to tell? The rattle is not altered by pushing in the clutch. I climbed under the can and it sounds like it is coming from the very front of the tranny vrs the rear. I will search the forum for additional info on the mounts and see what i can do to inspect them. First thing that came to mind was IMS failure but from everything I have read if these go there is little to no warning. The tranny noise has me most concerned. Andy

Finally droug the wife out to the garage at 10:30 tonight to help me try and figure this out. My original conclusion was somewhat flawed in relation the the gearbox rattle I am hearing. The following observation was made after the car had had a chance to completly cool down. 1. The gearbox rattle is much quiter when cool vrs hot 2. Derprssing the clutch does does significantly reduce but not completly get rid af the rattle. I have read several posts that a LW flywheel will exibit more gear rattle than the dual mass version. I guess my next question is Are LW flywheels factory ot aftermarket? I have the receipt for when the clutch replacemnt was done. the only mention of anything flywheel realted is "Machine Flywheel $90" How common is gear rattle and what is considered normal vrs excessive. thanks, Andy

From what I have read the flywheel on these cars is either in good shape when inspected and reused or replaced. I would be suspect of it being machined (resurfaced). That said, check the mounts first.

I think this may be your clue. Any Porsche dealer knows better. Some Indy's may not. It is not recommended that the flywheel be resurfaced. There is a simple pass/fail test for the DM function and surface check. Regardless of mileage, the flywheel is 14 years old and should have been replaced (@$450) not "machined" when the clutch job was done. I would try and find out a little more about the shop and exactly what work was done. I suppose there are many other possibilities as to the cause but the clutch job and flywheel work is a "red flag" to me.

LWF are not stock on these cars. If you still hear it with the clutch depressed it is not from a LWF. That rattle is from gear clatter caused by not having the vibration damping effect of the Dual Mass Flywheel (DMF). If the rattle is present when the clutch is depressed with the trans in gear & the car stationary it is most likely not something in the trans itself. Because in that situation nothing in the trans is turning. I would suspect the DMF in that case, also possibly the throw out bearing. TSB 911 (996) 8/02 1360 Dual Mass Flywheel Check procedure http://www.renntech.org/forums/index...-procedurepdf/ Can the dual Mass Flywheel be twisted approx. 15mm in each direction (0.590�), left/right, and does it return to approximately its initial position? If so it is good. Can the DMF be twisted beyond dimension stated above without a noticeable increase in the spring force? Or is it fixed (no rotation?) if so bad

Some animation of one type of DMF and U-tube of good vs. bad DMF 3D animation of dual mass flywheel - YouTube Dual mass flywheel worn new vs Old - YouTube

Is gear clatter typically constant? The nosie I have hearing seems to fade in and out every 10-20 seconds. I am planning on putting the car up on jack stands tonight and redoing the following check If the rattle is present when the clutch is depressed with the trans in gear & the car stationary it is most likely not something in the trans itself. Because in that situation nothing in the trans is turning. I would suspect the DMF in that case, also possibly the throw out bearing. I am also planning on draining the gear box and inspect/replace the oil. I will report back on my findings. Should I assume that the car is non drivable at this point? Thanks, Andy

Non drivable? That is a tough call. You don't say if you hear it when the car is in gear underway. I would fix it sooner rather then drive it if that is the case. If it is a "light" rattle only when the car is stationary at idle it I would probably drive it while making plans to fix it. I would recommend using the Porsche trans oil. As with any lube there are many opinions on this. I have used non stock gear oil and found that the two I used caused very stiff shifting when the trans was cold. Mobil Delvac synthetic 75w90 and Ultron 75-90 YMMV The most common gear clatter in a 911 is caused by variations in engine power pulses when the trans is not under load at idle. In the past Porsche used rubber centered clutch disks. The rubber would start to break down and cause problems. The trick fix was to use a spring centered disk as a replacement. This caused noticeable harmless , but to some irritating, gear clatter at idle. It would fade and get louder as the speed of the internal bits of the trans change in relation to the input shaft (engine) speed.

fpb111 First I what to say thanks for your responses. I am feeling a little better about things, Still need to pull the tranny i think and take a look at the flywheel at a minimum. once the car is up in the air and I can get under it I will have a better chance hearing any gear rattle above Idle. Currently I can only hear it at idle. I will attempt to catch a audio clip of it with my phone if possible. As for locating approved gear oil that appers to be more or a problem then originally thought. Can not get it locally so I am going to have to order some in. Other than OEM porsche oil are there other porsche approved brands? Andy

My car had a rattling sound coming from the tunnel area behind the shifter. I took out center console and noted the shift cables would vibrate a little against the metal chassis of the car at certain rpm. I stuffed some foam rubber between the cables to isolate the vibration from the car and the noise went away.

Glad you have decided to check the flywheel as suggested. As for trans oil, nothing beats the Porsche oil. Best price (they ship fast) is probably here at this well known Porsche dealer: http://www.suncoastparts.com/product..._Code=996Trans Please keep us posted.

Put the car up in the air last night so I could take a closer look at things. I have verified the following. 1. The gear rattle is only present at idle with the clutch disengaged, engage the clutch and there is no more rattle. 2. There is no sign of the rattle at RPM's higher than 1K. 3. While it was up there I drained the gearbox and found no signs of any foreign matter in the oil, it was a greyish black in color and the typical gearbox oil type order ot it. I refilled the gear box with Redline 75W90 NS GL-5 just to get me buy until I drop the tranny in the next few weeks. I will order the good Porsche stuff for the re-install. Car still drives and ****s perfectly; the rattle is still there at idle. The vibration seems to come and go. It presented itself during last night’s test drive but not during this morning’s drive to work. My plan is to still drop the tranny and take a look at the DMF to see that’s going on there as soon as I can carve out the time and make some arrangements to call in some favors. Andy

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To state the obvious then the noise is the normal tranny rattle these cars suffer from. Some more than others. My 02 Boxster with over 268K miles hardly makes any noise at all and the 03 Turbo even before it obtained its current 109K miles would once in a while have the tranny rattling. But a guick dip of the clutch pedal quiets the rattle. The modification you made to the exhaust could account for some increase in the rattle as the engine now idles less smooth than it did before. About the only way I know of disproving this theory would be to fit the stock exhaust, but I could certainly understand if you elected to not do this.

Mac, I think one of his concerns was that someone machined the flywheel. I suppose none of us know at this time if this is a stock OEM DM flywheel or an aftermarket one. If its an OEM DM we all know machining or resurfacing is a no-no. We are WAG'ing at this point but I have no rattle at idle or otherwise, clutch in or out but I also have all new parts including flywheel. I dont think he would be over reacting to at least drop trans if he wants to inspect more closely. I thought he mentioned vibes and noise at other RPM's too but maybe Im wrong. I would still check into the shop that did the work and ask exactly what they did.

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I still wouldn't rule out the engine mounts and that helping out as it seems like you are saying at idle you are hearing the noise (probably due to some vibration). If the mounts have never been changed (and its a '99) it a quick easy thing you should do anyways. While I was doing my alternator a couple weeks ago, I also swapped out the mounts on my '01, and now at idle the car vibrates much less (used the passenger seat as my before and after test)

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Not sure where you got the resurfacing the OEM DM flywheel a no no. I've come across cars in for new clutches at dealers and in some cases the FW is sent out to be resurfaced. As long as the FW's DM feature checks out ok and the tech can't find any other reason (excessively overheated, cracks) to reject the FW they're ok to reuse, with or without resurfacing. Treated right they'll give good service life as the one in my 268K mile Boxster is an example. Not all cars have as quiet a transmission as your car. Some can be a bit noisy but this is not a sign of anything really wrong. Just the normal differences between cars. Also, a slightly rougher running engine -- as might be possible with an ill-advised exhaust system modification -- can exacrebate the rattle. Thus given if the same exhaust was fitted to your car it might make as much noise as the OP's. As for dropping the transmission I'm not at the car so I can't really offer any guidance other than to advise the OP to have a professional tech give a listen and if he thinks the noise warrants further investigation to go along with the tech's advise.

Mac, I assumed you knew better. The info is straight from the manufacturer who builds them, LUK. I dont think youve seen any Porsche dealer having OEM LUK dual mass flywheels resurfaced. They just replace them. Im not saying this is his noise problems, but it calls into question the repair shops competence.

This is all so new to me that I am not sure if I am over reacting to a non-issue or if I have a real problem. I am more or less satisfied that the gear rattle is a common issue so I will monitor it to see if it gets worse. The vibration issue however is worthy of an expert opinion there a few local specialty shops that have good reputations both locally and on the forum. Seems a few $$ is well spent. from that I can get a good feel for what if any issues there are and what the best course of resolution is. You guys have been great and i will keep you posted. Thanks, Andy

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If your going to drop your tranny to inspect the flywheel, are you planning on inspecting or replacing your IMS bearing? I am definitely not a IMS-gloom-and-doomer like many on this forum (cough, KK, cough), and don't usually advocate preventatively replacing them 'just because', but if the tranny is down, 2/3's of the work is already done and it might be worth either putting in the LN ceramic kit, the pelican kit, or source your own $20 ceramic bearing. The Redline GL-5 gets lots of extremely positive recommendations from 996/997 owners, even more so from the track set who occasionally have 2->3 shift issues under high G / high RPM loads. It's what I plan on using on my next tranny fluid change, so I'm curious to hear back how it works for you. The only real complaint that I've read about some other top quality but non OEM gear oils (e.g. Delvac) is that some folks have more 'cold shifting stiffness' than the OEM (999.917.546.00), which I think is a Shell product? Don't know where you live, and reasonably certain your not going to get much cold weather anytime soon, but I say stick with the Redline and give us an update!

Here's a thought. The symptoms described sound a whole lot like the kind of noise I got when I replaced my otherwise fine DMFW with a AASCO LWFW. Prior to this exchange there was no transmission noise - none. I wonder if the car had a LWFW already and that was what was resurfaced. I can't see how resurfacing a DMFW would cause noise - the vibration dampening properties of the DMFW wouldn't be affected at all.

"1. The gear rattle is only present at idle with the clutch disengaged, engage the clutch and there is no more rattle." I'm a little slow please help me understand this sentence. "Disengaged" = foot on the clutch - pedal to the floor or pedal up foot off pedal?? You might be looking at the effect and missing the cause. Your car calls for plugs @ 30k intervals. When was last plug change? Also check the coils for cracks while you are in there. If the engine is running slightly rough it will aggravate "normal" gear clatter. Also a louder exhaust will cause more vibration in the car. Different bits will vibrate when the pressure waves from the louder exhaust hit their resonate frequency. I noticed this in my car when I did the first style PSE/Gundo Hack/Fister mod on my car. Pic 1 is the first hack done like Porsche's Sport Exhaust (PSE) without the OE vacuum silencer switch Pic 2 is louder and as I understand it the hack Fister does on all of the 996 cans now.

Let me summarize Gear rattle is present when when foot off clutch. Vibration most present when foot clutch depressed to floor and RPM at 3400. Plugs where replaced at 60k by previous owner. To be honest the more I think about it the vibration issue presented itself about the same time I installed the Fisters. Andy

As a note the exhaust mode fister did for me looks like pic #1

As Macster said: "Some gear rattle at idle is normal. With some trans louder." If you don't have whine when under pressure accelerating/driving trans bearings are probably good. If the rattle goes away with clutch pedal on floor ?probably? not DMF. You wanted louder you got louder. Go enjoy it.

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No where in my Porsche references can I find any warning about resurfacing the dual mass flywheels used on Porsches. From LuK's web site, I did come across a reference to refacing that cautions: Scoring, glazing, and/or gouges indicate that the flywheel has been overheated, and these must be removed, however they should never be refaced beyond the tolerances laid down by the manufacturer. In another document at the LuK site, I find that as is the case with with other items, like oils, the OEM refers one to the vehicle manufacturer for the last word on the use of the item. "What should be considered when installing a DMF? � Observe the specifications of the vehicle manufacturer!" But your info does raise some questions. Maybe the techs are going against the official guidelines and resurfacing when they should not be? While this is certainly a possibility I find this hard to accept as generally they are more conservative. A component failure from unsanctioned resurfacing means the dealer eats the cost of the subsequent repair. For a dealer to go directly against what the factory recommends would I think call into question the accreditation of the dealer. Besides there is the profit margin from a new flywheel vs. just a resurface, unless I guess as some would offer up and that is the customer is being charged for a new FW when the old one was just reused after an unsanctioned resurfacing. I'll keep this in mind and see if I can learn more. I can use an excuse the fact my Boxster has so many miles and is getting close to needing a new clutch and should I budget for a new FW at the same time.

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It is good to see a summary to make sure we are all on the same page... Gear rattle of a mild sort that then has the rattle in the realm of they all do that can be present with the clutch disengaged. It should go away when the clutch is depressed. Whether it comes back after the clutch is released again right away is questionable. In my experience if I do nothing else it does not. If I rev the engine then sometimes as the engine slows to its normal idle speed the noise comes back. Revving the engine with the clutch pedal depressed subjects the bearing to extra and unnecessary wear and tear and as I like to avoid unnecessary wear and tear I do not do this. Any revving of the engine is made with the transmission in neutral and the clutch engaged, the clutch pedal fully released. Thus I can't say if what you feel is normal or not. There are obviously times when driving my cars that I engage the clutch certainly with rpms in the range of 3400, or below or even above, quite a bit above. But I notice no vibration or signs of anything amiss. It could be your car has a less smooth release bearing or one that is perhaps going bad. Not a diagnosis just a thought. My only experience with a failed release (throwout) bearing is it was fine, no symptoms, until I depressed the clutch to start the engine -- as I had about a zillion times before -- and upon the engine starting what proved to be the throwout bearing emitted a piercing squeal and did so every time I depressed the clutch as I drove the car to the dealer to have what proved to be a failed throwout bearing replaced, along with the other clutch hardware. I'm not at your car and I can't experience the severity of the symptoms to know if they are within what could be considered normal or not normal and thus suggestive of a problem. So this vibration at 3400 with the clutch depressed I think needs a professional's attention if nothing more to say that's normal and to have someone tell you to stop doing that. As for the exhaust system... The change to the exhaust system can affect the engine/drivetain vibration harmonics. The engine/exhaust/drivetrain is a carefully tuned assembly to deliver acceptably good levels of performance -- we all are aware of this -- but to also deliver acceptably low levels of NVH (noise, vibration, and harshness). This sometimes we forget when we go making modifications to this assembly. Does the vibration appear at the clutch pedal if you just place your foot on the pedal but do not put any pressure on the pedal and rev the engine to 3400 with the rest of the conditions the same and the transmission in neutral?

Mac, just so you dont think I just make sh#$ up this has been discussed on this forum before and is stated on several LUK / clutch manufacturer websites. LUK does not recommend resurfacing ANY of their DM flywheels. LUK has a really nice PDF that explains a lot of info. Straight from LUK's "Clutch System Diagnostic Guide" I wouldnt be surprised if the OP's DM flywheel has been replaced with a solid flywheel, hence the gear rattle and vibrations. He wont know until he drops the trans.

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I never suspected you made things up. I too found the info at Luk's site you posted. But I again scanned the factory manuals I have and no where did I find any caution against resurfacing the flywheel. Certainly Porsche is not shy about cautioning against wheel repair, non N-rated tires, not reusing some fasteners or other hardware, even spelling out how much tire slippage on a wheel is permissible. I mean almost every page has at least one caution, warning, or note on it regarding what is proper and allowed or not allowed. So it is hard to imagine Porsche failing to put something in the manual about not resurfacing DM FWs if indeed this was a no no. There might be a separate document that does caution against resurfacing the DM FW but I have not seen it, not been made aware of it. Anyhow, my Turbo -- just short of 110K miles -- is due to be serviced (oil/filter) very soon, maybe Friday if the dealer can fit it in, and I intend to bring this up when I drop the car off as my Boxster is getting close to needing a clutch. Well, not that close but with its miles I think a discussion about a clutch job would be timely.