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slight grinding noises from the drive shaft


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Hi All:

I've had this mysterious grinding noises for about 2 years... I took it to a local repair shop today and the owner told me he's heard the same grinding noises on a dozen cars and still can't figure out where the noises come from.

The car is a 2002 996TT with tiptronic. Whether it's on 2nd, 3rd, 4th, 5th gear, at around 2000 RPM, when under a slight load (accelerate), a distinctive grinding noises can be heard; the noise seems to originate from the drive shaft (center to front, but not from the rear of the car). This would last for a short second. As soon as you pick up speed (RPM) the noise would go away.

I've read some place, where Porsche made a public notice that this happens to a specific tire set (the Michelin PS2). The grinding noise comes from the front differential. Porsche says it's not a problem. Some ppl with the same tire set never experience the problem. Or some ppl with different tire set still experience the problem.

Do you guys who own 996TT experience the similar issue? It never causes me any problem; it just bothers me somewhat...

BTW... What's the proper differential oil for 996 TT? 75~90 spec or higher?

Thanks guys.

CW

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He's heard a griding noise on a dozen 996TTs? Hmm....that's news to me and i own one. I have a 2002 996TT manual and I can tell you that I definitely do not get a griding noise from my transaxel (differential) at any RPM range in any gear. The transaxel as a unit is crisp, smooth, and quiet. When's the last time you changed the fluids? What kind of ATF and gear oil did you use? Also, I don't understand fully what you're saying about the tires. Using a certain brand/type of tires should not make the differential grind.... and if it's the tires making the noise I would think you would be able to tell.

I don't have firsthand experience with the tiptronics but I'm fairly certain you should not hear a griding noise. I suggest getting a second opinion or trying to identify what's causing the noise. I don't mean to alarm you but if there is a problem in your transaxel it's not going to get better. Metal-on-metal contact in these transaxels, due to lack of lubrication or the wrong type of lubrication, can damage all sorts of expensive parts including gears, pinions, etc. It would be worthwhile to identify what's causing the noise.

As a tangential note, the only "irregular" noise on these cars is that the engine tends to rattle at low RPM. However, this is totally normal and not a cause for concern on the TT.

Also, have you looked specifically at the wheel bearings?

Edited by Silver_TT
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He's heard a griding noise on a dozen 996TTs? Hmm....that's news to me and i own one. I have a 2002 996TT manual and I can tell you that I definitely do not get a griding noise from my transaxel (differential) at any RPM range in any gear. The transaxel as a unit is crisp, smooth, and quiet. When's the last time you changed the fluids? What kind of ATF and gear oil did you use? Also, I don't understand fully what you're saying about the tires. Using a certain brand/type of tires should not make the differential grind.... and if it's the tires making the noise I would think you would be able to tell.

I don't have firsthand experience with the tiptronics but I'm fairly certain you should not hear a griding noise. I suggest getting a second opinion or trying to identify what's causing the noise. I don't mean to alarm you but if there is a problem in your transaxel it's not going to get better. Metal-on-metal contact in these transaxels, due to lack of lubrication or the wrong type of lubrication, can damage all sorts of expensive parts including gears, pinions, etc. It would be worthwhile to identify what's causing the noise.

As a tangential note, the only "irregular" noise on these cars is that the engine tends to rattle at low RPM. However, this is totally normal and not a cause for concern on the TT.

Also, have you looked specifically at the wheel bearings?

Hi Silver_TT

Thanks for the reply! Here's what I got the info from about the tires: http://porsche996turboblog.blogspot.tw/2010/07/issue-clanking-noise-while-accelerating.html

The wheel bearings have been repacked and service.

Regarding the type of fluid for Tiptronic, is it the same Mobilube PTX that is used for the manual transmission that is recommended? Both the transmission and the differential fluids have been replaced not long ago; however, I can not recall if the noise happened after I had replaced the fluids... I'm not sure what type of ATF was used, but will check asap! Maybe this is the cause of the noise?!

Thanks.

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got it. He used Redline 75w-90 LS on my Tiptronic transmission and the differential.

Oh boy....... The Tip and differential use totally different types of lubricants, the TIp uses an ATF like product, while the diff should have a 75W-90 gear oil in it. If he really put the same thing in both, I surprised it works, much less makes noise..............

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got it. He used Redline 75w-90 LS on my Tiptronic transmission and the differential.

Oh boy....... The Tip and differential use totally different types of lubricants, the TIp uses an ATF like product, while the diff should have a 75W-90 gear oil in it. If he really put the same thing in both, I surprised it works, much less makes noise..............

(*&^%^!! What's the right fluid for the Tip? Differential fluid should be Delvac 75w-90 then?

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got it. He used Redline 75w-90 LS on my Tiptronic transmission and the differential.

Oh boy....... The Tip and differential use totally different types of lubricants, the TIp uses an ATF like product, while the diff should have a 75W-90 gear oil in it. If he really put the same thing in both, I surprised it works, much less makes noise..............

(*&^%^!! What's the right fluid for the Tip? Differential fluid should be Delvac 75w-90 then?

The Tip calls for ESSO ATF LT 71141 or its equivalent; the 75W-90 should be fine in the diff.

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Sorry, I misheard... He used ATF (porsche-spec product) on the Tiptronic; Redline 75w-90 on the LSD...

That's much better. Ask your mechanic how he adjusted the level of the fluid after refilling the trans (there is a specific proceedure to do this), otherwise the trans may not have the correct level of fluid in it.

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Are you running Michelin tires? I read that TSB and it sounds similar to what you are describing but states there is a rattle -- not a griding, as you stated. I don't mean to argue semantics but to me there's a big difference between a rattle and a grind.

JFP is correct. There is a specific procedure for adjusting the level of fluid. You have a transmission in your car that runs well north of $10K for a reman replacement from Porsche (not counting labor). I would definitely be sure you're both running the right ATF and gear oil, and be sure the mechanic followed the specific procedure. Having too much or too little fluid (or the incorrect fluid) can permanently damage the gearbox.

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Yes, I'm running on Michelin PS2's. It's not a loud bang; however it's loud enough for you to notice it, though very briefly. Kind of similar to an engine knock... If you go down a gear and not hitting the ~2000RPM range, the noise would never appear.

I'll have the mechanic check on the tranny fluid level tomorrow. We are having a huge typhoon day today!!

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Well, the jury is still out on this one. After draining and replenish the LSD with Delvac 75w-90 (where it was Redline), the rattle/grinding noise is... still there, but much reduced and harder to reproduce. I'm happy with it at any rate. $100 for the change, which I think is worth it. Well see if on my next tire change, this would be gone for good!

Thanks guys.

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Well, it seems that it must have been the differential then if changing fluids drastically reduced the problem. How long had the non-OEM oil been in there?

Please follow-up on this post at some point in the future when you change to different tires. As a fellow TT owner, I'm really curious to see if this completely solves your problem.

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If I remember correctly, it was the noise that prompted me to have the LSD fluid changed, transmission fluid changed, and one leaking wheel bearing repacked and sealed, but without success. The noise continued. That was about 15 months ago. So the Redline gear oil has been it since then.

The mechanic who was with me during the test drive also confirmed that the noise comes from the drive shaft.

The noise seemed to have appeared when I've replaced the rear wheels with PS2's about 18 months ago (yep, I'm surprised they lasted that long!), but I can't be ceratin about its timing... Other than the noise, the car drives fine.

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If I remember correctly, it was the noise that prompted me to have the LSD fluid changed, transmission fluid changed, and one leaking wheel bearing repacked and sealed, but without success. The noise continued. That was about 15 months ago. So the Redline gear oil has been it since then.

The mechanic who was with me during the test drive also confirmed that the noise comes from the drive shaft.

The noise seemed to have appeared when I've replaced the rear wheels with PS2's about 18 months ago (yep, I'm surprised they lasted that long!), but I can't be ceratin about its timing... Other than the noise, the car drives fine.

I'd really like to know how they repacked your wheel bearings, they are sealed units:

99905304104-M34.jpg

I am beginning to think that you need to have another set of eyes, ones with a bit more Porsche experience, look at this car. Your "grinding" noise could be wheel bearings, or CV joints; but someone that tells you they repacked bearings that can't be repacked needs to be replaced..............

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I'm sorry, I misunderstood your post #3 in response to my original post saying to check the wheel bearings -- I thought you were saying you had the bearings "replaced". Given this information, I think you have to at least reconsider the assumption that this is not your wheel bearings. If they were leaking that means there was a lack of lubrication and I would have replaced with the OEM part at that time. I concur with JFP that it might be time to give someone else a look.

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I don't know if 'repacking the bearing' is exactly the right term. The wheel bearing or something close to it (oh, I think a joint from the hub to the wheel) had a leak. They fixed it by replacing the bushing. It's not the bearing itself. Sorry about the confusion.

I imagine if it's the bearing, the noise would be there all the time. The noise (rattling/grinds) I hear only appear at 1800~2000RPM. As long as you select a gear that would skip this range, it's fine.

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Hmmm... not sure based on the information you have posted since it's not exactly clear.

I still wouldn't rule out the bearings and would look at the CV joints though. The front wheel bearings are "known culprits", and I use that term somewhat loosely, in some of these cars. JFP may have more experience but just because you only hear a noise at a certain RPM still doesn't rule out the aforementioned.

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OK. The noise is gone!! I finally had all 4 tires replaced yesterday. I didn't go with the factory spec. I went with 215/40/18 and 285/30/18 combo, only because I could get the rear ones of a certain brand (Federal RSR 595) much cheaper (about 1/2 the price) than the choices of 295/30/18 that I have... The combo has a slightly narrow width but the front and the rear match in rev/mile.

Yep, the noise is no longer there. It's very possible that the PS2's that I had didn't go well with the RE001 in the front (they were both factory spec). Replacing the LSD oil with factory-spec oil reduces the frequency of noises (could not be reproduced so easily) and changing the tires completely eliminate the noise issue.

Something that bothered me for a long time finally went away... I'm happy now, but It's kind'a funny how such a little noise can bother you so much...

BTW, the T1R (215/40/18) and RSR 595 (285/40/18) is supple in ride quality. A bit softer than the RE001/PS2 combo that I had, but as a DD, I like it this way. The RSR 595 is a bit slippy in rains, however.

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People do not realize how a tire can affect your cars performance and input sensors. I was called to a shop to diagnose an intermitted ABS issue. The tech at the indie was going crazy with a right wheel sensor code. He changed the wheel sensor that threw the code no change. He then changed the other three wheel sensors no change. He decided to change the yaw sensor no change same issue. Now the shop had several thousand dollars in time and parts invested without any answers.

Thats when I was called in to see what I could find out what was going on with this problem car. I first scanned the car with a factory tool to be sure shops generic scanner was not sending them down the wrong path. I then checked all the wheel sensors with a lab scope to prove they were all working properly. All passed with flying colors so did the yaw sensor. I looked at the tires they look almost new low mileage maybe 10 to 12 thousand on them. Now what, this was a real mind twister.

I remembered a friend of mine that use to be in the tire biz as a factory rep for several big name companys. He told me stories that the engineers were always playing with exotic belts and compounds and they would have weird issues all the time. Then the MFG would change whatever to make a quick fix until there next problem.

Now back to the issue at hand. I had the shop swap the rear tires with the front. I know there larger than the fronts but there was enough clearance they did not hit the fenders. The owner of the shop thought I was crazy. Now for the test drive on the same route without any issues. After the test drive my diagnoses was new tires all around the tires on this car where shot! The belts where moving in a way that the wheel sensor was thinking the wheel was slipping/skidding? The ABS module started pulsing the right wheel doing what it was designed to do. So the moral of the story is just because the tires are low mileage and look ok they might be the culprit.

Edited by binger
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