Cayenne unusual steering wobble - extraordinary.

[racdavies]

Hi all,

Preamble - I have had a 911 4s but swapped to a Cayenne S because the two kids couldn't fit in the back.

Problem - I have had the Cayenne for 6 years and know it very well. FSH and no expense spared. However, some time this year at higher speeds only and only when slowing from those speeds a tapping wobble has been coming through to the steering. Almost like going over cats eyes or thick road markings. Rhythmic. This is the weird bit - If I gently touch the brakes, it goes away, foot off and it comes back, but only at higher speeds does it do it at all.

I have replaced the wishbones top and bottom at front, all front bushes, had wheels balanced and replaced disks and pads front and back but it still does it and it's driving me nuts to know why.

Does anyone know what might wobble on throttle off slowing from high speed and touch the brakes and it disappears until you take your foot off the brakes again?

Been to two garages and had other handy mechanics look and we're stumped.

Many thanks for thinking...

Richard

[Cobnapint]

Strange one that. As it comes in when off throttle but goes when on throttle or braking suggests to me a bit of play somewhere in the drive to the front wheels.

Could a drive shaft bearing (if they exist) or something in the front end transmission be worn...?

Dunno.

[NAS90]

Go to a competent tyre and alignment shop, given the work you have had done to the front end suspension already and the issue you describe, get the wheels & tyres off and spun up on a balancer to check they are running true just to eliminate them as a source, then get a wheel alignment done to check alignment is spot on after the suspension was apart for wishbones and go from there.

A competent mechanic doing an alignment will also flag up any play in the steering joints, suspension, bearings, etc. as they'll find any play whilst they are trying to get a perfect alignment.

From what you describe i suspect you have an alignment issue that is magnifying minor wear in the steering joints, but having not driven it that is an educated guess at best....

[edh]

Wheel bearing?

[ScienceTeacher]

It could be a resonance from engine / gearbox / propshaft mountings. The braking is consistent with disrupting the resonance. It is a specific well defined problem. Someone with specific experience of this needs to deal with it. Otherwise people spend a lot of money on fixing non-problems. Our nanny had this same problem with her Golf (given, it's a very different car). It was a gearbox mounting resonating and could be fixed by just bolstering it for free or replacing the mounting. She spend hundreds sorting out non-problems before an astute tech identified it in 5 minutes. She had declared the car as almost undriveable beforehand.
I once had a wheel bearing go on a Focus and there was a thumping resonance and reverberation over a range of speeds, the frequency consistent with the revolutions of the wheel. I don't think you have this. I also had my wheel balancing fail on a front wheel on a 996 C2 and there was an annoying resonance through the suspension detectable through the steering wheel which was a specific frequency and onset was between 73 and 85mph. It was not there above 90 or so. I did not try seeing if it returned at 150...

[RPTIME00]

Has your cardan shaft been replaced yet? They all go eventually on 955s, but your symptoms don't describe a typical failure.

[red997]

given what you're replaced already, my money is on the cordon shaft / bearing / mount;

Assuming these haven't been replaced ?

Its a fairly common complaint on KN's

[racdavies]

Thanks all. Well, there has been a development I think. I am away on vacation for a few weeks and left the car at the local garage. The best mechanic on our island (remote) came with me and drove it and managed to get it to do the thumping too. We'd already ruled out all shafts and shaft bearings and replaced suspension bits (actually new bushes has helped stiffen up the ride so not totally wasted).

He seemed to think it was an ecu issue and as though the suspension PSM and ABS were all fighting each other. Why only at certain speeds I don't know?

But psi has been kicking in going round left hand corners at low speeds recently and it hadn't been in the past so some kind of inertia sensor maybe at fault? What became interesting was that we could make it happen at 60mph by swiftly wiggling the steering wheel briefly and it'd start the resonance off. Beyond my understanding but he seemed to know what was up and I've heard via the grapevine that the car is out of the garage, so maybe sorted? If it is I will post what the cure was.