mnotz

So the '87 Auto is coming along rather nice. TB/WP/Intake all set. She runs nice, still some electrical gremlins to hit and a few other things, but I still can't figure out this noise it's making. Originally thought it was in the flywheel area, but pretty sure now it's further back. In the car as well as outside of it, it seems to come more from the area just about where the shifter sits, so definitely quite a bit further back than the flywheel. It's always there, neutral, drive and reverse, rpm-dependent. It's quite loud in the cab, just about overpowers the exhaust note (RMB). Coasting along, or just very light throttle to just keep speed on no incline makes the noise sometimes almost go away, but as soon as you accelerate it's back. Never had a TT bearing go bad, but could that be it? End play was checked, flex plate had a bit of a bow originally, but was released. It seems that right after doing that the noise wasn't there for a few hundred yards, but then came back.

Here is a video that kind of captured the noise on youtube: I really appreciate any help!
Thanks in advance,
--Marcus

gazfish

Is the trans fluid level correct, could be pump noise due to under or over filled.

FredR

If you released the clamp because there was a small level of distortion on the flex plate, the mystery noise disappeared and then returned shortly afterwards the obvious thing to do would be to check the clamp again.

The notion that simply releasing any preload and then tightening the bolt again "fixes things" is somewhat optimistic to say the least.

The noise that you describe seems somewhat unusual but the fact is you appear to have identified the approximate location and anything that attenuates the issue is presumably relevant.

Presumably your example has the 25mm shaft [i.e. no taper section behind the splines]?

Constantine

If there was a loaded flex plate, that means there was pressure both forward and rearward.

At the back there are two bearings in the torque converter housing that are probably ruined. These are usually noisy after a loaded front flex plate incident.

This is besides the TT bearings which were also operating under load and most probably ruined as well.

Discerning exactly where the noise is coming from is very difficult since the TT transmits the noise throughout the TT.

HTH.

mnotz

Thanks for the replies!!!

The trans fluid level is correct, but I was planning a trans fluid/filter service this weekend too. There was definitely a loaded flex plate in the car when I got it. First thing I did when I got the car a while back was to throw it on the lift and release the tension and check the end play. Luckily end play was within specs, but the flex plate was loaded quite a bit. See https://rennlist.com/forums/928-foru...l#post17461348

This noise just doesn't sound like any bearing noise I've ever heard before, which is why I figured I'll ask the experts around here that may have run into something like that before. The car seems to have the tapered shaft by the way. At the mileage (shy of 110k) it's probably time to throw some Super Bearings and new TC bearings. I didn't plan to do this until the middle of winter and enjoy the car until then if I could have found a different reason for that noise, but worst case I rip into it now. I mean, the front of the car was apart already, guess I can continue with the rear...;-) Is there a source for the TC bearings, or are they just plain old universal bearings a supplier would have?

Thanks again,
--Marcus

zekgb

That's the noise my driveline made as the TC bearings in my 85 failed at 105k miles. It will eventually turn into a grinding sound that you won't be able to ignore.

mnotz

Oh yay! I can't ignore that noise already now! Makes a mess of the 928 sound ;-) You are talking about the two bearings towards the front, before the TC? Where did you source yours from? Since the TT has to come down for that anyway, I mine as well do the bearings there too in the process.

Thanks so much!!!

zekgb

Yes, there are a pair of bearings in the Torque Converter carrier that need to be replaced - Roger should have the SKF replacements. You should definitely rebuild the TT at the same time, I used Dwayne's writeup (which is great) but ended up having to R/R everything three times after carelessly dropping the Torque Converter in the bell housing on reassembly and breaking the dog ears on the transmission pump. I do not recommend this method.

https://rennlist.com/forums/928-foru...re-w-pics.html

mnotz

Awesome info! And I try my best to not drop the TC in the process! Damn. That must have been one of those moments...so sorry to hear that! Bet you know that area of your car rather intimately by now!

Thanks for your reply, much appreciated!

FredR

21 years ago when my torque tube shaft snapped, upon handing over a new torque tube to the local agents that I imported from the US the first thing the chief mechanic advised me was to replace the torque converter bearings. I had complained as to how a shaft can snap at 50k miles and was told there was nothing wrong with the design! That being the case how did they know to change out the torque converter bearings? When I put this to Porsche they had no answer. When the original bearings were extracted the chief mechanic [who became a good long term friend] showed me the bearings and one of them was "rough"- this after only 50k miles. I then got the internet at home and found Rennlist and it transpired that this issue was well known then. I subsequently concluded that the flexplate clamp could not retain the imposed load and this explained why TBF occurred, why 28mm shafts snapped, why torque converter bearings failed prematurely and why torque tube bearings failed prematurely. Stop the clamp from migrating and these problems do not seem to happen- we have seen examples that covered 300k miles with no issue but then their clamp did not slip. Once the clamp starts slipping it is something of a crap shoot as to what level of attrition is taken by the various components in play.

Assuming this is what has been going on and based on your original thread indicating 5mm of movement it seems a good bet that it is, the last thing you should be doing is re-using the original bolt and "hoping for the best". If the noise is the torque converter bearings then whilst dealing with this you should get yourself one of Constantine's amazing clamps and get rid of the problem once and for all. You should also get yourself new pinch bolts for the front and rear clamps. Fitting a set of Constantine's Super Bearings is also a no brainer irrespective of condition- just based on time based degradation of the rubber mounts is sufficient justification.

Finally, if you have the taper shaft fitted you would do well to carefully inspect around the base of the taper for any signs of surface cracking- a dye pen or mag particle inspection [both ends] is the best precaution one can take short of a new shaft- visual inspection may reveal something but...?.

Nothing special about the bearing races in the TC - they can be had from any bearing factors if you have the model number.

mnotz

Hi Fred!

Thanks for your detailed reply! Really crazy this happened to you after just 50k miles! This is my first auto 928 aside from a parts car I had, so new territory on this end of the car for me. I already had ordered new bolts for the clamps, just haven't installed them yet since I just this week got done with TB/WP/Intake and Transmission. Transmission service, etc was next on the "catching up on years of deferred maintenance list", and eliminating this noise, or better, the reason for it is high priority. This car is going to be in that bay of my shop for a while longer, there is plenty to do still. Considering the price I paid for the car, the condition body and interior is in, and the fact that I keep and not flip cars justifies the investment in it, especially since I do all work myself.
I also just this morning dropped Constantine an email, so there will definitely be some super bearings in the '87 along with TC bearings and whatever else comes along while I am working in that area.

Again, thank you for your reply. I am glad to have some better idea of what might be causing the noise. I guess my thinking totally didn't go into direction bearings because the noise sounds so different from any bearing noise I've ever heard. Makes sense though. The bearing amplified by the aluminum bell, travelling through the TT might make all kinds of weird frequencies appear that are quite different from just a regular noisy bearing.

FredR

Marcus,

I cannot relate the sound bite to being the TC bearings but it would not surprise me at all if that is the root cause of the noise you hear. That you have had issues with slippage of the flex plate is what it is- a major clue to the puzzle. The thrust bearing can seemingly withstand a degree of pressure from slippage of the clamp but at some point it gives up the ghost and then the damage is catastrophic as in terminal. 20 pus years ago my clamp was slipping and after the new shaft was fitted the problem announced itself in that after about two weeks of running a signature vibration at precisely 3050 rpm would appear and then i knew the clamp had slipped. Porsche, who were adamant there was no technical problem with the design, were put under the hammer by me in that I refused to take the car back unless they came up with an answer- with this in mind the local agents took the problem back to Germany and within 10 minutes or so got a response to fit a new bolt and over torque the bolt by 10%- we did this and two weeks later the vibration was back- their solution was useless! I discussed the problem with a couple of top notch mechanical engineering colleagues and we concluded that some kind of bonding mechanism was the only likely solution. I was also advised to get a home internet connection and do a "google search"- I did and found this list. One of the chaps on the list [Earl Gilstrom] advised that he was going to use Loctite 290 and I followed his lead. It worked for me and to this day still holds my flexplate. However, whereas I am confident it works in my local [hot] climate I would not know if it works in a different temperature range and whereas it has held firm and probably still will, I have never specifically recommended its use but I have advised a good number of folks how to apply such.

At the same time as I joined the list I also passed a comment that I could not believe that on such a critical application like this that Porsche would use such a primitive clamp design and commented how if I were going to design something like this I would use a taper clamp approach. Shortly after I posted this Constantine contacted me off line and advised he was designing exactly such a piece of kit and we shared thoughts on such. This is the kit Porsche should have designed and they should have had a recall programme to retrofit such. The irony is that had Porsche stuck with their original design involving shims non of this would ever have happened. I now have one of Constantine's clamps waiting to be fitted- it really is an amazing piece of kit that all 928 automatic owners should fit- no questions asked!

The other major affliction that I suspect will impact all 928's sooner or later is the issue with cylinder head corrosion. I have written a fair bit about this in various threads and given your capabilities and interest you might do well to consider such problem given you have long term ownership in mind. I may well start a thread on this subject to catalogue my findings to date for record purposes. If you have history about head removal in the not too distant past all well and good but if not you might want to research this potentially major problem some that we see and hear of more and more as time marches on.

the flyin' scotsman

to isolate the noise you can disconnect the TT from the flex plate and start the engine. Undo the clamps on the shaft and flex plate then push the joining piece t othe rear until it clears the flex plate. Starting the engine briefly will quickly determiine if the noise remains or not..........if not then you know where to look for sure.
Remember the TT shaft is turning all the time with the engine running even with transmission in park.
Also with the lower bell housing off (engine off) put a measuring tape down the TT to determine distance to the forward bearing; they tend to move with time and wear, good luck..

mnotz

Fred, thank you for the additional insight. Yes, I am certainly planning to keep all of my cars on the road for a while to come. That's the goal with the cars I find or the ones that find me, as sometimes happens too. LOL. I have an 86.5 which will have a heads off procedure once I get around to it, the 87 will hopefully be a while until it gets there

Malcolm, even though I am fairly certain now that the noise is coming from somewhere further back than the engine area, this is a quick and easy way to confirm, especially since the car is often "parked" on the lift anyway. Not sure why I never thought of doing it! Thank you!