Kolbjorn S

I have this funniest noise, when driving along, depressing the clutch and breaking, a loud "clonk" appears from underneat the car. When accelerating, nothing can be heard, but a repeated breaking will reproduce the sound. The car (5 sp; 65k miles) shifts and drive nicely, although the diff (mechanical type I guess n this '87 model) does produce some grinding noise while turning at low speeds.

If I bang with my hand on the rear 1/3 or so area of the transaxle, there is a sound just as if something is loose inside it (nothing seems loose around it, including the gear shaft straight above it, so it appers to come from inside). But I had a look at another transaxle that was out, when peeking into the tube I see on each side of it a large bearing sealed by very thin rubber against the circular tube wall. Q: What's behind these bearings, that I can't see - only the shaft going through or something else that can break and cause the sound? Is there a link to a picture somewhere how the transaxle looks like on the inside, or its components?

Vilhuer

Not sure if this applies to your model year. There is vibration damper between 2nd and 3rd bearing inside TT on some model years. It may have disintegrated for some reason. Check Service Info Tech 1991 S4 GT page 3-2 for picture what it looks like. Document is part of CD's made by Jim M. For pictures of dismantled TT see this thread. https://rennlist.com/forums/928-forum/178818-torque-tube-rebuild-pictures-and-tools.html I left damper in so do not have pictures of it. Been meaning to take picture of it while it's inside TT and probably will when tube is cleaned.

Kolbjorn S

Thanks, I'm not familiar with the reference you list - do you have a link to the picture of the harmonic dampener? What does it look like and how big it is? If that is a large-ish metal piece attached to the shaft, and has come loose like you suggest, it can explain the clonking sound I hear, both while braking and while knocking on the tt with my hand.

There is a small play (3-4 mm?) where the right side drive/half-shaft enters the differential (ie if you pull on the differential connection of it, it moves in and out a bit); but I'm not sure yet what the tolerence is for this, as it seems normal on most cars... I wonder if that also could also contribute to transfer some clonking noises...

Vilhuer

Don't have picture online. Damper is maybe 15 cm long heavy thick walled metal tube supported from it's ends. When all is ok it isn't in any way in contact with center shaft, just "hangs" around it canceling certain frequency (have seen number 64Hz mentioned) vibrations. If it gets loose from mounting rubbers it will probably make some serious noise.

3-4mm play isn't that much so I do not believe worn differential to be the source. On other hand TT is strange in a way that it can transfer noises and make them seem to come from totally different source than what is actually causing them. One possible source could be loose mounting clamp in gearbox input shaft. If that's it, center shaft bores will look horrible. Do check to rule out this ASAP if you can. One other possibility inside TT might be bearing supports themselves. They can move and for example if outer rubber and bearing move but inner small tube stays put on center shaft bearing needs to move only 2 cm's before it's totally off from inner shaft. This would probably cause some kind of noise.

Get in touch with Jim Morehouse or John Speake if you want to have Jim's CD's. Best investment you can make. I can't imagine how people manage without them.

Kolbjorn S

When tilting my tt from one side to the other, there is something moving inside relavtively heavily from one side to the other. So what I suspect, is that this is the vibration damper.
If indeed the damper in my tt has come loose, any idea if it can be fixed or a replacement found?? I'm a bit worried taking the shaft completely out if there is such a damper inside.
Also, I wonder what model years and/or AT/5sp have the damper installed?

Vilhuer

Factory documentation I have seen only concentrate on '90 and '91 model years. I have heard damper being in '88 S4 automatics TT and this one case bearing supports were different design what we have on hand now. In S4 case to change bearing it was necessary to drill six rivets away that held support halfs around bearing. I wouldn't install any tube back to car if it makes any kind of unwanted noise. These dampers can't be that important any was as some cars have worked without it for years. So fear of having usable damper isn't important IMHO. Picture from factory docs showing two different designs.





Center shaft goes through dampers center hole leaving some mm space between them. If that heavy looking pipe gets away from it's end supports it has to make some noise. There might be more types other than these two. Support inside my TT looks like #1, at least it's ends does looking from outside of tube. Based on this thread have desided to take it out to make sure it stays together.

Kolbjorn S

Erkka, thanks alot for your useful information! Tube from my car is now open, and it's got three bearings (right side in the picture) and a huge 1+ kg heavy vibration damper (left side):



Here's an overview of how the parts are positioned relative on the shaft (with my freshly machined flywheel in the back...) - left is rear, right is towards front of car - the damper is situated in the middle between the 2nd and 3rd bearing:




So - with great help from the Porsche-dealer in Muscat, SATA llc, we found the source of the annoying clonking sound heard under braking: The vibration damper has a large rubber seal attached to each side of it, and one of these had failed so much that it got separated from the damper. This left the damper sliding between two of the bearings. Luckily it seems not to have touched the shaft itself though. This is what the worn seal looks like:



I sourced the three bearings from the SKF outlet here in Muscat today - part "SKF 6006/2Z/JEM", although they are annotated "6006/2Z/C3". Size is 55 x 30 x 13 mm, it's a closed bearing so it should be great with regards to thermal resistence.



Next excitement is if I succeed in finding a machining shop to make me replacement rubber seals for the damper .... ideas anyone?

To be continued!

Kolbjorn S

I almost sourced new vibration-damper rubber seals from a shop who makes them in Germany, but ... never got the right address. So, I ended up using the damper seals from the donor tube - that tube was bent anyway, but the damper seals were ok.
After installation did a dirty and simple single bolt into each of the damper seals (the seals are actually made of metal but covered in rubber). This should be easily retractable in case of future repairs (god forbid). But ideally I think it would be best to put screws just before/after the damper without touching the parts themselves.
Interesting project!

Peter F

Good work on the tube and very good pics
What tool did you use to remove and replace the bearings?
Any pics?

Cheers/Peter

Kolbjorn S

Shaft removal: The local Porsche-dealer sourced and applied this tool - it is a tool used on axels on large (Scania) trucks - very similar to the excellent tool which Villhuer made - see this tread. This clamps on the tube, and you then "twist" the shaft carefully out.

Bearing / damper removal: No particular tool, but some brute force (carefully applied!) is required. An example is a plate of a diameter slightly less than the inside of the tube itself, and some metal stick of some sort. You might try to push the internals out by muscle force. It that does not work more power is required .... well, get a lift, put the tube vertically beneath it, place the plate and stick in the tube, and (who-ho ) lower the lift *carefully* down onto it.... That worked in my case, but clearly you run a large risk of damaging the parts, so full disclaimer here! (keep a donor tube ready....)