clawless

Hey Everyone,

I am trying to diagnose an odd sound on my 94 968 tiptronic that appeared after I had the rear flex plate replaced and it's driven for a bit. It doesn't make this sound cold, only when warmed up. There is a very long story and it's been to a few shops with nothing found yet. We have only replaced the transmission mount, shocks and they have done the standard inspections for any loose/damaged bushings and the front damper has been checked and is fine. The odd part is the sounds were worse when I got it back from the flex plate replacement and initially sounded like the exhaust was banging the frame and was very loud under acceleration, and there was a grinding / binding sound when turning and accelerating a little hard. That all is gone and just this sound is left, and again, only when warmed up. You really can't feel it in the seat and there are no drivability issues, other than this noise that scares me to drive it.

It's been hard to record, but I was able to capture the clunk and its aftershocks for lack of a better word, maybe shuttering?.

This was recorded in a parking lot, after about 25 minutes of driving on the back roads. I am shifting from Drive to Reverse and back again. You can hear the squeak of the shifter as well as a bit of suspension loading creak, but in between there is the lower frequency bang, clunk, thud sounds, usually 2 or three back and forth or up and down.

The best way I can describe it is that it sounds like something bouncing up and down in a confined space and it's hitting the top and bottom of the confinement, like a bad sway bar end link or missing bushing or a really bad ball joint or a loose top nut on a strut. These sounds would also occur while driving, sometimes over bumps but not always, generally it happens with no rhyme or reason along with a sound which feels like the exhaust is touching the body but only briefly, that vibration and sound is not coming through on the recording.

Also attached is the visual representation of the entire clip, each of the spikes represent the noise and its aftershocks starting as seconds 6, 10, 14, 17, 21 and 24, with a few others in there as well. The louder ones are going from Reverse into Drive, softer ones the other way. The one at 24 seconds is the best recording I could get.

--Chris



968 clunk sound visual

fwb42

Check your CV joints..

walfreyydo

If you had the rear flex plate replaced by a shop, I would take the car back to the shop. Since the sound appeared after that flex plate work - that would be the first thing to check.

Probably related, wouldn't you say?

clawless

The CV's were checked and were deemed 'OK', but the (current) shop and I discussed I have new ones just in case, that is on the possible list and may be the next step.

As for the initial shop, that's part of the long story, and to me, these sounds are 100% related. I took it back after the flexplate replacement as these sounds did not exist before hand, it went in for a different sound which ended up being a broken rivet in the flex plate, but they had it again for a few more weeks and could not find the source of the new noises. They changed the rear shocks and adjusted the parking brake, those things made little difference. They ultimately gave up and they were not a true Porsche shop, they worked on the now older 24/44/68's in the 80's and 90's and I have used them back then for those cars and now for newer stuff. Its now at a Porsche only shop and they have had it twice for this, of course it never seems to make the noises when I take it in or they have it, but the finally did hear it this last time but they still cant seem to pinpoint anything and the fact its getting harder to reproduce, which is odd in its self is another mystery.

Tom R.

I have a 93 Tip with 72k miles that I bought this past summer. Previous owner parked it a dozen years ago because the flex plate is bad. I am not sure if that is the cause of the noise. Standing still I get a noise. Someone thought maybe the starter was not disengaging. I replaced the starter. No difference. It is a tapping. I will try to get a sound clip in the next few weeks. It is in the garage under a cover, and I think the car has to be in gear for the noise.

I am not having much luck finding the older mechanic that worked on these transmissions 20-30 years ago. The guys at the shops I spoke to know everything there is to know, so I have nothing to worry about. Just drop it off and they will figure it out. I am worrying!

How much did the flex plate job run you? I bought the Tip because my wife decided she will not drive another manual (back issues). Part of me is saying screw it, swap in a manual, but I want her to enjoy the car too.

I listened to your wav file. it sounds like rubber. the strut mount rubber when you turn. the sway bar bushing/end link? Is the car moving when you get that sound? Mine is more of a metal sound.

clawless

I'm at 88K mikes. I only get this noise when she is warmed up, putting it into gear like the recording (sometimes), and I do get it on the road as well, sometimes over bumps and such and I agree it totally sounds like a bad busing but why only when warm.

I also got the initial noise just standing still, and we could see the smoking gun on the rear flex plate with the broken rivet (once the trans was out) and now that's gone, but now new noises. It was about $2K for the rear replacement.

As I've gotten older, I got to be a lazy manual driver and with the 968 pinion issue, I went auto just to cruise, it still handles great and I'm not racing it or running it hard.

Tiger03447

It could be that the inner core of the cat has come loose and is clanking around. This is just prior to it disintegrating totally. Might bang on it a bit with a rubber mallet to verify the noise. If so inclined remove it from the E-system and do a more thorough check. Just a thought. HTH some.😀

clawless

Thank you for reminding me on the cat, it was one of the things I wanted them to check.

clawless

So they think its the Diff, but are not 100% sure. A used Tip transaxle is $2 - 3K, not something I'm going to replace without a 100% confirmation, they did find and fix a rusty exhaust bracket but no witness marks of it hitting, but I am a bit hopeful on that, and of course they have not been able to recreate the issue in their limited drive time, so now I guess I'm going to drive it until something breaks, not that I like doing that but they have gone over the whole car and checked all the bushings, brackets, fitting, etc. They did check the cat, front damper plate, motor mounts and things up front as well. Also they were reluctant do the CV joints as that sound gets worse over time not better, so they didn't think that was the problem. Have to make sure my towing coverage is updated!

Gage

Transmission mount?
I have found the late 944 single mount can produce a thump sound when worn. With the car suspended, manually swinging the transaxle side to side may be able to re-create the sound. I believe the 968 mount is different but similar in concept.

clawless

We did replace the trans mount, it was worn but not bad. Made zero difference.

If the exhaust hanger they fixed, which I still need to get more info on, did not fix it, I'm going to change the end links and sway bar mounts. That was removed when the original shop dropped the trans, the new shop check and did the prybar test, but say no issues. For my own piece of mind, Ill change them anyway, it is 30 year old rubber that was messed with.

clawless

So all was well for like 600 miles. I was able to recreate the sound only twice in that timeframe and only by hitting really bad potholes in a construction area, until Friday, it was warm out and I drove it for about an hour, then let is sit for about 15 min running, and then took off again, and the sound was back in full force, but only for about 10 min or so as I drove, then it was gone again. On Sunday I ramped up the back and looked again for what seems like the 100th time and nothing. BUT I don't know why but I had it in my head that it could be the resonator hitting a bracket as it looks very tight in there and when it gets hot it expands and as I drive it cools, so I decided to bend down the exhaust hanger that's on the back of the torque tube by the trans to drop the exhaust just a little, and when I did, I must have changed the angle just enough to unjam the 'hook' part that mounts to the actual exhaust. In the past this was a solid connection every time it was pushed, smacked or jiggled, but the angle change was just enough to set it free. As you see in the video, now its completely loose and the sound this would make is exactly what I hear, something trapped and jiggling within confined walls, loose bolt in a hole, that's tight enough when cold, but not when hot.

Also looking the diagram up, the hook is installed wrong, it has a nut welded on the back and should slide into the bracket on the exhaust tube and be bolted down, not bolted to the back of the bracket like it is now. The nut in the hook seems to have been stripped out at some point and someone moved it and bolted it down, which I'm sure was fine at the time. Of course, the hook is NLA for the 968, but I found one for the 931, which is available and it looks similar but instead of having a nut welded on it, Its got a stud, I'm hoping this is just a design change over the years, but the part still being the same size and shape.

Edit - the hook does appear to be available for the Tip, its the one for the manual that shows to be discontinued / NLA, not sure what the difference could be...

I've got it bolted back down now and have been unable to reproduce the noise. Gonna put ~100 miles on it tomorrow, that will be the true test, but really what else could it be?

clawless

Well that was it. All the vibration noises and clunking I was hearing and feeling are completely gone. Now I just have all the standard noises and vibrations. Including a rear hatch noise I had not heard before, time for a latch adjustment

My order was cancelled for the hook, it and the one for the manual are NLA. dC Auto has them, I may order one, and I may be able to re-tap the nut on mine or just crank it down with a grade 8 and just be aware if I hear noises again.

Now on to the cruise control for the second time...

Dr. 914

sounds like the ring gear and pinion. Often times when the car is driven for awhile with a broken flex disc, the drive tube beats the diff to submission

Tom R.

Would that make a noise when standing still in park or in gear? Now that spring is around the corner I need to get to work on my tip's noise. Thanks Doc.