FredR

Looking at one of the latest posts I wonder if the gent with the suggestion about exhaust fumes getting into the cabin has hit on something- if you drive with the windows open does it make a difference to the nausea sensation? I cannot believe anything mechanical would make you sick without it being so patently obvious what was wrong. Perhaps you can try one of those battery operated domestic CO detectors in the car and see if it goes off? It does not take much CO to make you feel light headed

You seem to have covered most bases. For sure a real nice looking example- I have heard of those flared front arches but have never seen one before [Jap market?]. Just one throw away comment- if you have fitted spacers presumably they have been matched to correct residual stud lengths- i.e. confirm you do not have a situation where the wheel nut is not able to put full tension on the wheel because of too much engagement however unlikely it may seem.

Your ride height looks like a factory photograph with the front end seemingly high in the air- it would be generally interesting to understand what ride height front/rear you are at relative to the index points.

Everything has a reason - keep plugging away and you will find the source of the vibration- presumably you cannot relate it to any specific action such as new tires or any component change- did it appear whilst in your stewardship or was it present upon acquisition?

Rgds

Fred

Pagnobito

It came from Japan with all the GTS updates including the spacers which I believe are genuine Porsche parts and fitted correctly.
It's an interesting idea about the fumes, we had the window open for a lot of the time and I don't think it made a difference to be honest. However I will check this again, it's more likely to be leaking from the joint between the cats and down pipes than a hole in the exhaust. It's in great condition underneath in terms of the body and fuel pipes at least.

It came to me with some problems and deferred maintenance that I've been working through including vibration, my view being cosmetic items harder to rectify than mechanical but maybe I'm going to change that view!

Bilal928S4

also might want to look in/under the center console that the exhaust gases are not coming up through the gear lever opening. If I recall there is a foam covering over the tunnel that keeps heat and fumes out.
More predominant problem in 5 speed cars.

FredR

It might be useful to eliminate the stud length as a problem- simple enough to do- with the wheel off engage the nut until it can go no further and compare this to when it "tightens" the wheel. I doubt this will be the problem but the more you know what it is not the closer you are to knowing what it is!

Regarding the possibility of fumes in the cabin there must be something available to use. Just a shot to nothing but why not pop by the local fire station, tell the lads there your problem and ask them if they have anything that might detect CO in the fumes/air space or hoe best to achieve the same- they may well have Draeger sensors for this purpose [what we use in oil refineries and the like] to accurately determine toxic air concentrations. if you try the open window method make sure both sides are open- anything to get some kind off through flow. These tubes cost about a fiver a pop but you are probably worth at least that! [see http://www.buydraegertubes.com/carbonmonoxide5c.aspx]. You could also go a for a spin until your head is a bit fuzzy and then pop down the hospital and ask them to analyse your blood- CO sticks to your red blood cells and causes your blood to stop adsorbing oxygen - thus why it is so toxic- small amounts being very noticeable.

Rgds

Fred

Bilal928S4

I also want to point out, if you have your windows cracked open, then it actually brings air into the cabin from all open orifices and exhausts it out the cracked window.

Pagnobito

Thank you for the suggestions, I realise I am chasing something that is not obvious but I don't think it's exhaust gas related as it is much more like you have been subjected to a low level sub harmonic vibration.
The foam on the TT looked very good and was the first time it had been off the car since it was new - you can usually tell if it has been touched before and the tape holding it on moved, it will also be tight against the body as it has new Volvo mounts that sit higher than stock by a few mm.
The wheel studs are fine and do not bottom out on the nuts so the wheels are secured. I am going to remove the spacers and check everything is good with those, the hub and brake rotor.

Pagnobito

I ran up the engine today from standing in N.

I get vibration through the seat from around 2500-3100 rpm and it's smooth either side of that although I didn't go above 5K.

I don't think it's engine as I would expect it do vibrate through the entire range or could a bad harmonic damper cause certain rev vibration?

Next test to confirm is to disconnect the engine at the flex plate and try again.

In N the only rotating parts behind the flex plate are the TT and TC, correct? So if it's good with just the engine running that is where I need to look. I know it's not wheels now as it does it while stationary.

FredR

The range of possibilities is indeed narrowing- I take it you have eliminated the [obvious] engine mounts from the suspect list by examination of how the engine sits rather than presumption based on age or the lack of it. Those vibe rpm's are mount suspect I would politely suggest.

Edit: I also note you have had the torque tube out- did you take any secondary measures to secure the flex plate clamp? Are you sure it has not migrated the commonly experienced 3mm shift? If you undo the flex plate see if it jumps when the tension is released. When you reset it paint some indexing marks on the splines so that you can easily tell if any movement has taken place. I take it you understand why I ask the question?

Rgds

Fred

Pagnobito

The Volvo mounts have less than 1K miles on them, the engine sits quite high, certainly above the bar.

The next test running the engine disconnected from the rest of the drive train will tell me where the issue is, or at least point me at one end of the car or other.

FredR

Check the flexplate carefully as you undo the clamp- on my 90 S4 it inevitably jumped back 3mm. This 3mm of pre-load caused a very distinct vibration at just over 3000 rpm - no where else. I would reset it, the vibration would disappear for about 2 weeks and then duly return. This happened just after I purchased the car in early 1999- the first I knew about it was when the drive shaft snapped. The vibration recurred with a brand new drive shaft & the problem was eventually solved thanks to getting the newly available Internet over here and with it access to Rennlist wherein the Loctite solution was proferred to me that I still rely on today.

Rgds

Fred

OTR18WHEELER

Bear with me on this....I had a vibration that was felt mostly in the steering wheel last year, had the front wheels reballanced, the tire tech guy showed me the wheel and tire while rotating on the balancer, the rim was true, but the tire was ovaled in the tread, the tire is actually out of round, not by flat spotting, just a less than premium tire.
also with the wheel off the ground there was some play in the wheel bearings, so I snugged up the hub nut. this eliminated some of the vibration, but not all. .... fast forward several months... replaced front wheel bearings, the ones earlyer mentioned were dry and burnt.
As for the Motor mount "go to" for vibrations in the drive train, I disagree., My MM's are 30yr old originals and hard as a 928'srus ball gag, but while the car is sitting on jack stands, with engine running, I feel no vibration in the chassis at all....
My honest opinion is left to three symptoms, listed in no certain order.
1) Wheel bearings, front or rear, could be just one corner bad.
2) Front TT Bearing has migrated rearward from the original position.
3) If rims are not in question, I suspect a bad tire, out of round or a shifted belt.

Any of these would cause a high speed vibration while driving.

Pagnobito

There was slight movement when I released the clamp for the first time when I dropped the gearbox and TT, my end float measured OK. I fitted a new bolt on re-assembly and it hadn't moved at all when I checked last week and fitted this; Flexplate clamp


I can check item 1. I've already covered 2 and 3 as I've inspected the TT and I have tried several different wheels and tyres and it has just had new tyres.
As I get vibration while stationary through 2600-3100 approx this would equate to cruising speed and you have to go quite fast to do more than 3100 rpm in 4th on the autobox. I haven't tried doing the same in 3rd but I think if I can cure the vibration that I can feel when stationary and at certain revs then it will also fix the cruising speed vibration. I shall do some more narrowing down this weekend by separating the engine from the drive train and see if it still vibrates in the same way.
Disconnect engine from TT at flex plate - vibration still felt? If yes then engine issue if no...
reconnect TT, is it possible to disconnect the TT from the autobox at the rear to just spin the drive shaft from the engine? I know there is a clamp but can't recall if possible to slide it off the splines toward the front of the car.
Depending on the outcome of the above I will be looking at engine, TT or torque converter.
Once repaired or replaced will run the test again while stationary and if all tests OK try the cruising and high speed test in case there are two issues here.

FredR

It sounds as though you have covered all the bases. Good to note you have Richard's clamp supporting your original clamp- I have no experience of this item- did you have the same vibration before you fitted this clamp?

If you are going to release the flexplate clamp and run up the motor to see if it isolates the problem you might also consider removing the Ritech clamp as an intermediate check to ensure that is not a part of the problem however unlikely it is/may seem.

Rgds

Fred

Pagnobito

The car has always had the vibration, the clamp made no difference, it's symmetrical and therefore balanced and a very good product. I've gradually replaced stuff and been thinking wheels as I only ever noticed it at speed and never thought to just gradually increase the revs when not moving. I will update with my findings in due course.

FredR

If the vibration was present previously clearly no need to eliminate the secondary clamp that from the list of possibilities.

It will be interesting to see what you find if you disconnect the flex plate. I know that the harmonic balancer can cause problem but I do not know how this manifests itself other than it should be a tight fit on the crankshaft. If the problem is on the engine side and it is not the harmonic balancer or engine mounts or crank end float then what else might it be?

If the problem is on the torque tube side presumably the rear tube bearing or the harmonic balancer [or whatever it is called] that sits between the two bearings become the prime suspects?

Whatever it is you are getting closer to identifying it. I am fully with you in that spurious inexplicable vibrations drive me crackers. In my case securing the flex plate clamp stopped the problem I experienced at a time when Porsche could not resolve it. When I linked the failed snapped torque tube to my findings they simply dismissed it on the basis it was caused by abuse!

Rgds

Fred