968.net

Tranny noises and strange knocks...any ideas please ?

Hello everyone, I have my beautiful 968 for 2 months now (107K miles) and was soooo happy but some clouds are becoming to blurr my happiness ! I'm hearing some metallic unusual noise from the back under, mostly at speeds over 50, when decelerating. I changed tranny fluid and there is no metal shredds what so ever, but noise still there. I googled a lot and it seems that transaxle pinion bearing failure is the usual suspect in this case...

Something else happened like 3 weeks ago, I was pushing the car a bit (but not too much) and got an awful sulfur smell - kind of natural gas - I read some place this also can mean my tranny is dying.

Another thing was some hard knocks coming from under the car when I was downshifting 4 to 3 (maybe 6000rpm in 3rd) I was really scared, maybe 5-6 fast and heavy knocks like something breaking under the car and hitting - I clutched to neutral and braked heavy and it stopped. I thought maybe some rev limit stopped the engine or so but I am pretty sure I wasn't in the red line. I was careful to brake before downshifting after then and it didn't happen anymore, but a few days ago I felt slight knocks again as I downshifted 3 to 2nd maybe 4000rpm which is pretty low !

 

Any of you have an idea what my problem would be and if these 3 symptoms are related ? I'm driving the car a few days a week but all have to be all smooth, I can now compare myself to those 65+ years olds that go out with beautiful Porsches and Ferraris all over Montreal for the F1 Grand Prix and run 40 km/h...I used to make fun of those people !

I was planning to do some mods to the car (nicer bigger wheels, exhaust,...) but I feel my budget is gonna go to transaxle and other maintenance...wellcome to the club you'll tell me ! I was expecting that but not thaaat fast.

 

Cheers,

Daniel

 

 

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There is an exhaust hanger about mid-way under the car, near where the front and rear sections of the exhaust system join. That hanger failed on my car at about 105k miles and there was random banging from under my car.

To replace the hanger, you have to separate the front and rear sections of the exhaust system, then loosen the Y-pipe where it connects to the header. A good penetrating oil (I used PB Blaster) is your friend for something like this. I was able to get all 10 bolts off without breaking them, and re-used all of them. Once I replaced that exhaust hanger, there has been no random banging and clunks from under the car.

Can't say for sure that's what you've got but you should inspect that hanger, at a minimum. Good luck!

Bob Kovacs
www.bobkovacs.com
Thanx, I will check that first, would be nice if it's only that !!!
Daniel, I would like to know what you found out on the knock situation. My tiptronic has a knock when going over bumps, the exh. hanger sounds like a likely culprit. When I have time, I will have to lift the car and check out the hanger. I will also check the transmission rubber mount, wwhich is the only thing actually holding the transaxle.
Hi Ken, I passed by the mechanic today, he told me the rear shocks are tired so that might cause knocks when I downshift because it shakes them too much...
I will get the car up next Monday for other stuff and will check exhaust hanger and the tranny mounts as well, I will keep this updated then.
Cheers
The smell could be the clutch going away.
I had the car lifted today for fuel filter change, transmission mounts are good and exhaust hangers good as well...I'm starting to believe the rear shocks are knocking when downshifting as my mechanic says...and my shocks show they are tired.
I had the clutch checked, it has 30 mm distance from slave cylinder to clutch house, clark's garage says 18mm for new and more than 38 for finished...so I'm in the last quarter of it.
yep but the stock disc is rubber centered, if you still have the stock type disc, it can go bad before the disc wears out, as happened on the 6-speed, according to the p.o., the clutch components had been changed, (and they did look fairly new) but one side of the disc completely separated from the plate. I had to do the clutch disc, master and slave cyl. and other related components.
Failing CV's or a loose exhaust hanger could also be causing the knocking noise, so don't be too quick to decide you need to rebuild the gearbox. A failing clutch center could also make some of the same noises. Be thorough in troubleshooting it, if its your r$p, you'll know it soon enough. [EDIT] After I posting, I saw everyone elses comments, sorry I am late to the party!

Its probably not the tranny mount, by the way. I helped a friend swap his out last weekend trying to diagnose the same symptoms. He showed up with the tranny mount (170k miles on his 968) as that's what his diagnosis was, so we went ahead and installed it, but it didn't make the problem go away, in fact it was worse when we are done, which makes me suspect the cv's.
Hi Scott, funny thing just tonight I had my best friend test driving the car and he had the "under seats knocks" while downshifting, but only from 3rd to 2nd gear !!! (So I was mistaken at the beginning of the thread I thought it happened when I went from 4th to 3rd gear in fact it probably was 3rd to 2nd) Anyways we then tried same kind of driving with 5 to 4, 4 to 3, even 2 to 1st and nothing happened...so I'm really thinking about something inside the transmission/ clutch?
Forgive my ignorance (English is my 3rd language and I get lost sometimes) but what is CV ?
Thanx again for the inputs, knowledge is always wellcome !!!
I will let you know if I find some solutions...
Daniel
CV is the constant velocity joints that connect the transmission to the wheels(through the half shafts).
My TIPtronic is up on the stands right now. I am replacing all 4 CV joints as there was some noises that lead me to believethey need replacing.
Since I had the same knocking sound, and thumping that could be felt on the floorboard as Daniel J.
(see earlier posts) I checked the exhaust system for anything loose. I could not make anything knock around while the car was still on the wheels, but once I got it up on the stands, I found that the resonator, the triangular muffler looking thing connected to the rear of the cat. was knocking against the exhaust tunnel.
I removed the exhaust system from the cat back for cleaning and to make it a little easier to get to the CV joints, and could see actual points of contact on the resonator and tunnel(there is actually some kind or brace or heat shield that was being hit).
I knocked the brace or heat shield with a hammer, hopefully creating a bit more clearance, and did the same with the resonator. Just a small amount of a dimple.
I can do some adjusting on the hanger itself in order to let the resonator hang slightly lower, I don't believe it would take much to keep it from hitting, probably just the hammer mods would work, but I don't want to have to re-do this if possible. I would like to provide a margin for error.
I am not sure if the rubber mount at the hanger was completely on or not. By thre time I had gotten the exhaust removed, the rubber piece could have slipped off the hanger slightly. I will make sure it is fully in place upon re-assembly.

Daniel, I know that you said there was a good measurement for your clutch, but from experience, unless you have figured the smell you were experiencing out, I would take the cover off and inspect more closely.
My clutch was fairly new, but I had a total delamination of one side of thr friction disc, and would not have believed anything was wrong with the disc until I took the inspection cover off.

good luck,....Ken

I have the same thumping on downshifts epically to 2nd. I’m repacking and adding new seals to my cv’s (20 year old rubber can’t be long for the world). Also, I’m replacing the rear shocks with Bilstein’s. I don’t see a problem with the exhaust. If the problem persists I’ll get a Billy boat cat back and new mounts (almost $1000 is an expensive 10 hp, but fun). While I’m on jack stands I’m doing front rotors and carbon pads(tired of matallic dust) since I need to repack the front bearings and add new seals. Busy weekend epically since my 8mm tri-square wrench only lasted through 22 of the 24 cv bolts.

I have experienced the "knocking" sounds that you describe. Mine turned out to be the inner baffles of the exhaust system. Once replaced, which was not cheap, the sounds went away. When I heard the sounds initially, I would have sworn that they were coming from the drive train.

 

BTW, I have a tip and I have replaced the damper plate on it once. When the damper plate went the second time, I had my transmission modded to use a clutch plate instead of the damper plate. That was four years ago and I have never had to deal with replacing the damper plate again.

 

Cheers,

 

Bill

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