Will somebody please give me a definitive solution?
Discussion
phelix said:
It might be worth another rennlist post but use simple English so that the Americans can understand it. 
Been there before, they are terribly pedantic and entirely too technical with little or no 'user' benefit ito real world descriptions.
Plus, the sense of humour bypass appears to be a be a national affliction.
I couldn't give a sh1t what the dyno sheets say but it is critical that The Kessel Run is a mere 5 parsec inconvenience...
Billy Ray DeR.
DeR
Unless the direction Alan has provided is the answer, I think you have to start a careful process of elimination - one item at a time (others have said this I know).
The wheels must be an obvious candidate as the culprit, and running on a different set should eliminate that fairly quickly - if you have always had the same set then I would definitely try this.
From that point, I'm guessing alignment, track rods, 4WD disconnected and so on.
Unless the direction Alan has provided is the answer, I think you have to start a careful process of elimination - one item at a time (others have said this I know).
The wheels must be an obvious candidate as the culprit, and running on a different set should eliminate that fairly quickly - if you have always had the same set then I would definitely try this.
From that point, I'm guessing alignment, track rods, 4WD disconnected and so on.
I've had a few too many glasses of plonk so this is probably bollox.
I had a bizarre vibration problem in my early 993... turned out to be the rear PU valance being loose due to the mild steel struts having corroded through. What did for mine was a crazy race to a ski resort in Switzerland... the salt finally rusting through the struts.
At speed, the airflow around the back set up a resonance in the rear PU (which was now free to move about as some of the struts had failed). My local indy said they've never seen the problem... however after fixing mine (12 months ago) - I returned to get my brakes fixed last week and they'd had a few 993s in for exactly the same problem. Given mine was an early car, perhaps 993s are starting to get the rear PU struts corroded through?
In my case the vibration felt like the crank had gone (big end bearings)... in reality it was nothing of the sort. Slowing down lost the vibration, as did stopping and starting again. Bizarre really.
Also, duff brakes cause all sorts of odd vibrations through the drivetrain, though I'm sure that your brakes are always kept in tip-top condition. Mine, sadly, were not, as a result I now have this knowledge...
I had a bizarre vibration problem in my early 993... turned out to be the rear PU valance being loose due to the mild steel struts having corroded through. What did for mine was a crazy race to a ski resort in Switzerland... the salt finally rusting through the struts.
At speed, the airflow around the back set up a resonance in the rear PU (which was now free to move about as some of the struts had failed). My local indy said they've never seen the problem... however after fixing mine (12 months ago) - I returned to get my brakes fixed last week and they'd had a few 993s in for exactly the same problem. Given mine was an early car, perhaps 993s are starting to get the rear PU struts corroded through?
In my case the vibration felt like the crank had gone (big end bearings)... in reality it was nothing of the sort. Slowing down lost the vibration, as did stopping and starting again. Bizarre really.
Also, duff brakes cause all sorts of odd vibrations through the drivetrain, though I'm sure that your brakes are always kept in tip-top condition. Mine, sadly, were not, as a result I now have this knowledge...
grant3 said:
Dere,
I know you love this machine, but it is time for a change, a new challenge a new love.
Sometimes you miss the beauty & only see what is wrong,despite changing everything, this is time to move on!
If you don't rate the 996TT, then maybe a GT2?
A new beginning......
I know you love this machine, but it is time for a change, a new challenge a new love.
Sometimes you miss the beauty & only see what is wrong,despite changing everything, this is time to move on!
If you don't rate the 996TT, then maybe a GT2?
A new beginning......
Grant, after this morning's near lethal run out (roads of PURE grease) the concept of 2wd fills me with horror, it really does and living in the UK's rain capital, grip is, er - relevant!
I'm sure a 996 w/psm would have coped admirably but yesterday, having taken the old girl into work, I actually walked over the road to take in the profiles from astern and afore: it still oozes charisma and to some sad extent, is as much an object d'art as a driving tool per se which is a ridiculous thing to state, especially after nearly 7 years!
Actually, that drive out was so lairy I'm feeling quite unnerved as I sit here...
Cripes.
Bor - no, it just feels like it's generally going to seal your fate in any direction.
Tertius, Cyber - will pass on all ideas to Tech Central - many thanks, especially that corrosion theory, hmmm...
Mind you, it's fookin' rapid; I mean, searingly, planetaxially lungeworthy - maybe excessively so? Dear oh dear...-
The only time i have ever come across a vibration linked to application of power is:
For engine speed vibrations (mega hard engine mounts resulting in Vibration white finger for the pilot)
For drivetrain speed vibrations (worn UJ creating an increasing eccentric drive shaft / prop shaft.
I suppose its possible wheel bearings could do it i think it would be obvious when you jacked up the car and gave the wheel a tug.
Good Luck !
For engine speed vibrations (mega hard engine mounts resulting in Vibration white finger for the pilot)
For drivetrain speed vibrations (worn UJ creating an increasing eccentric drive shaft / prop shaft.
I suppose its possible wheel bearings could do it i think it would be obvious when you jacked up the car and gave the wheel a tug.
Good Luck !
Interesting this as I get much the same on my 993C4S which, apart from the power, isn't so different. I have a dire vibration on lifting off, just like a totally out of balance front wheel. It last from about 80mph down to 50mph and then goes. On speeding up, it comes back at about 58mph but is gone by 65mph. Wheels are balanced OK and on some road surfaces it doesn't happen at all ie. on a race track.
Long shot, but all Porsche 4wd systems are designed to run with identical diameter tyres front and rear, so even slight variations can make a difference. Check the manufacturer specifications for the boots you are using - the common measure is "revs per mile" - you may be surprised as there is a huge variation in this number between supposedly identical tyre sizes from different manufacturers.
DeR very sorry to read that you haven't managed to nail this problem - I remember you posting about it a while back.
Some small things I can add;
Its not the power/torque, there have been some serious 993tts out there with 4WD and 650hp/800NM and no resultant vibrations.
Since new, my car has never had any vibration problems other than wheel balancing - so as long as the chassis is straight its going to be that process of illimination.
I remember you changed back the flywheel to dual mass and mentioned how much smoother it was - I never quite understood this, the LW flywheel does not make that much difference, it should only add a rattle under load at low revs in higher gears (mine is worse than MODs but still a non issue)but I was always told that over 500hp and the dual mass is a hinderance.
I would be tempted to go in the direction Vic is pointing - is it possible to take off the front drive shafts/diff and propshaft and see if that works ? The only problem with doing this is you will get such a buzz from the purity of the helm that you won't go back !
Some small things I can add;
Its not the power/torque, there have been some serious 993tts out there with 4WD and 650hp/800NM and no resultant vibrations.
Since new, my car has never had any vibration problems other than wheel balancing - so as long as the chassis is straight its going to be that process of illimination.
I remember you changed back the flywheel to dual mass and mentioned how much smoother it was - I never quite understood this, the LW flywheel does not make that much difference, it should only add a rattle under load at low revs in higher gears (mine is worse than MODs but still a non issue)but I was always told that over 500hp and the dual mass is a hinderance.
I would be tempted to go in the direction Vic is pointing - is it possible to take off the front drive shafts/diff and propshaft and see if that works ? The only problem with doing this is you will get such a buzz from the purity of the helm that you won't go back !
Well Der, I can't assist you with your vibrational issues but....
"searingly, planetaxially lungeworthy"
...if that isn't the the most wonderful description of our combined obsession then I'll gladly eat a hairy football.
The treble mot juste and no mistake.
Good luck with it mate.
br d
"searingly, planetaxially lungeworthy"
...if that isn't the the most wonderful description of our combined obsession then I'll gladly eat a hairy football.
The treble mot juste and no mistake.
Good luck with it mate.
br d
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