tbarcelo

Hi all,

Re 2003 TT, 36k miles vibration

I have searched many of the "vibration" threads and virtually every one blames tire balance. I have been fighting a highway vibration felt in the front end (steering wheel) for a few months. While I had the tires balanced when I bought the car (about 15 months ago), I have since replaced the rears. I decided to try to get the fronts balanced, but the shop told me not to bother - they were too worn. So here's my current setup:

Fresh (and freshly road force balanced) 235-35-19 Nitto Invo tires on 997 Turbo wheels (the triple-split five spoke style)
~1yr old (also road force balanced at the time) 315-25-19 Nitto Invo tires on 997 Turbo wheels

The vibration is most noticeable on the highway and always seems to be worse right away (I know, this indicates flat spotting); however, it never seems to really go away. Furthermore, I noticed it both yesterday and today (i.e. drove back-to-back days) with temps never dropping below 75F (unusual conditions for flat spotting).

What else might cause a front end vibration? Common front end suspension weariness on these cars? While the car has just 36k miles, it is eight years old.

Thanks.

Macster

Assuming you can trust the balance job and the tire tech's attention to detail and hopefully noting if a tire (or wheel) had excessive radial or axial runout, one fairly easy thing to check is the inflation pressure of the tires.

Get yourself an accurate dial (or digital -- I have both) tire pressure gage and check the tire pressures cold. Start with the factory recommended air pressures.

What I found with one of my Porsches (but I've never tried to reproduce this with the Turbo) is overinflation of the front tires produces a vague vibration that mimics or at least feels like a tire imbalance but of course is not.

If you find the tire pressures ok then you're left with other possible causes.

The quality of the tire balance then becomes a possible issue. But even before this one possible cause is the wheel may have lost a weight. These sometimes are not applied very well, especially if the wheel is very dirty. Or the weight can come loose during washing the car if the water hose or wash wand pressure is high and the force of the water directed right at the weight.

Before you have the wheels/tires rebalanced you might remove the weights (or remove one weight and note its position and weight value) and take the car to another tire balancing facility and have the wheels rebalanced and see if the rebalance not only comes up with the missign weight and location but has a positive effect on the vibration. The first place may have simply botched the job.

May I point out too that you classify the vibration coming from the front end but you still must consider the possibility (slim I agree) the rear wheels/tires may not be balanced properly.

Are the front tires *identical*? Not only are they same size but is their age approximately the same, their hardness, and so on? Are they directional tires and are they both mounted in the right direction of rotation?

The integrity of the tire needs to be considered: A 'bad' tire one that has a manfacturing defect can result in a tire that balances but still can produce a vibration. Another sign a tire may not be right is how much weight was required to bring the wheel/tire combination into balance. I don't recall the numbers but if a tire or wheel requires above a certain amount of weight to balance this suggests the tire (or wheel) may be defective.

Then the integrity of the wheels needs to be considered. Bent or damaged wheels can give rise to vague vibrations. Also there is a callout on both radial and axial runout that is permissble from wheels so even if the wheels are not bent per se they can have too much runout and should not be used. But one would hope the tire tech would see this runout during the balance operation.

Next the mounting of the wheels to the car need to be considered. A wheel that is not quite centered or has something that came between its hub face and the hub can result in a perfectly round and balanced tire/wheel assembly being well wobbly and vibration can result.

A more long shot possibility is if the wheels you are using are suitable for the car and each other. If they are not, the mismatch of the wheels may be a contributing factor. A swap of tires/wheels (see below) may help answer this question.

Wheel alignment should also be considered. Not only should the alignment be on the money but you want to make sure that the car can hold an alignment., because....

Because while the number of miles on the car is not large various suspension and steering and drivetrain components can fail at anytime so if you have eliminated all of the above the possibility a shock or some other suspension component may be bad and the vibration results from that. And if a suspension or steering component is bad then one possible clue (besides the vibration) is the car may not hold its alignment.

Do the brakes pulse when you use them? Have you given the brake rotors and wheel hubs a good inspection? What about the front drive shafts and even the Cardan shaft? Remember anything that rotates can cause or contribute to a vibration.

If you take reasonable steps to find the source of the vibration and are unsuccessful maybe you can arrange to swap front wheels/tires from a Turbo owner and see if swapping tires/wheels has the vibration following the wheels/tires to the other car, or with the swapped tires/wheels remaining with your car?

You might -- I am not certain about this so you should probably go slow and get confirmation -- but you might be able to swap the front and rear wheels of your car and see if the vibration moves to the rear of the car or the vibration or other vehicle behavior is modified in some way that provides you with a clue as to what's going on.

Alot of, I hope, useful info I know. I wish I could say the problem is caused from "bad tire balance", "wrong alignment" or whatever, but I can't. All you can do is take reasonable and ordered steps to eliminate what the cause of the problem is not until you find the cause.

Sincerely,

Macster.

tbarcelo

Macster - thanks for the very thorough, and well thought out response.

I had three interesting drives today. The first to work which prompted my post. The second in the middle of the day where I felt far less, if any, of the vibration. The final drive home from work I noticed some vibration, but it almost felt more like a seat of the pants / rear wheel out-of-balance type vibration.

I do have some modest pulsating upon braking, so I know that my rotor/brake setup is not perfect.

The tires are the same make/model, were manufactured within about 18 months of each other. The wheels are Porsche wheels designed for the 997, but fit the 996 (using proper tire sizes).

I would really love to borrow a set of known, vibration free tire/wheels, but alas, my attempts to do that locally failed. Perhaps I'll try again.

Thanks.

SSST

Could be a number of things, but I have heard of problems going to a 997 19"setup on the 996 because you can't get the tire diameters between front and rear close enough. It can cause problems with the front differential and/or PSM. The standard 996 setup has a 0.1" difference between F/R, the tires you have are 0.4". It doesn't sound like much, but it might be enough to be causing the problem.

It could also be that you simply need new front tires.

I'll be interested to see what the problem actually is.

Good luck

tbarcelo

SSST - I have remedied that problem with proper tire selection. The difference in front-to-rear revolutions per mile varies from 2 (OEM Contis) to 14 (OEM Bridgestones) for the OEM tires. My Nitto Invo setup varies by just 6 revs/mile.

I have been paying extra close attention to this issue during the last few drives, and I'm starting to wonder if I have a strut problem (or other suspension issue) or some kind of worn bushing / mount. I say this because the sensation really seems to vary from drive to drive and is very difficult to pin down.

Thanks for the inputs ...

deckman

Same issue here, it varies. I have Pzero N2's

tbarcelo

Okay, so I'm continuing to work on this issue. I have a different set of tires / wheels on the car running stock sizes (225/40/18 and 295/30/18). This has definitely improved my vibration issues, but I can still tell that something is going on.

Question for the experts - I definitely feel considerably increased pulsation when I brake. Is this likely to be warped rotors or is it possible that I have a failed (failing) bushing or suspension component that causes mild cruising vibration but something much more noticeable when braking?

Can any of this be attributed to a failed (failing) wheel bearing? Any easy ways to diagnose this stuff? I'm a bit leary of taking the strategy of simply replacing stuff until it goes away!

Thanks,
Trevor

Pmafia

Just a thought, check your underbody panels. If any of them are loose or broken they can easily cause vibration at high speeds. I had a highway vibration that I couldn't resolve. Poked around underneath the car and found that the drivers side rocker panel was missing the rubber lip in front of the rear tire. The PO must have ran over a high curb or a rock took it out. I replaced the whole rocker panel since the mounting for the rubber lip was cracked off. It reduced the vibration significantly but I still had some. I took a look at the passenger side rocker panel again. While the rubber lip was there, the plastic part of the rocker panel that it was mounted to was cracked. I could move it easily with my hand. Replaced that rocker panel and now no vibration. The aerodynamics underneath the 996 turbo are precision engineered and a slight variation can cause unwanted results.

Land Jet

My tire guy told me the Pirelli Pzeros had a belt shifting problem which causes problems. I had them as the original factory tires and when I got rid of them, the ride improved markedly.

To the OP, have you considered that wheel bearings could be the problem? Others have experienced this.

tbarcelo

Land Jet - wheel bearing has been one of my suspicions. It might be responsible for the highway vibration as well as the pulsing (which I think may be getting worse) when breaking.

Is there a good way to check wheel bearing health?

Macster

Brake pulsing seldom arises from warped rotors. More often the reason is due to the brake rotor developing areas of different coefficients of friction.

Since the brake rotor material is very homogeneous the cause is due to uneven pad material deposition.

How can this happen? One reason is the brakes were not properly bedded in before they are used for hard braking. Another reason is, and I've experienced this directly with another car, is that the brakes are rusty and before the brakes are used enough to remove the rust the brakes are used for hard braking.

In either case above if the car is brought to a complete stop and the hot pads remain in contact with the hot rotors some pad material is left on the rotors.

My experience is that even in a mild case of this happening nothing short of a rotor resurface will correct the situation. Fortunately in my case the pulsing was mild and only occured under very light braking which I tend to avoid for reasons I won't cover here, so I lived with the symptom for quite a few miles even selling the car (with over 120K miles) with the original brakes.

Now once this uneven pad material deposition takes place, over time as the brakes are used the rotor can develop wear patterns that results in out of parallel rotor surfaces, as the rotor wears unevenly due to its now uneven areas of friction.

In your car's case the pulsing may be exacrebated by worn steering, suspension components. One can't rule these out with a 'new' used car.

For the brake pulsing consider having the rotors resurfaced if they have enough metal to tolerate this process. If the pads are ok you do not need to replace them, but the old pads and the refinished rotors will have to be bed in again. Premilimary to the brake rotors being resurfaced the automotive machinist should view the rotors and advise you of their overall condition. If one exhibits excessive axial or radial runout the rotor should be replace. And if one side of one end of the car gets new a new rotor I'd recommend replacing the other side as well, unless the rotors are quite new.

After the above, if you still detect something amiss when braking at least you know the brakes aren't directly responsible and knowing this then points you to looking elsewhere for the cause of the symptom.

After the brakes are taken care of then if the symptom still appears you should consider having the steering/suspension inspected by a tech for any signs of problems.

There are not many things you can do besides setting the tire inflation pressure, having the wheels/tires properly balanced (and hopefully at the same time any bad wheel or bad tire id'd and dealt with), ensuring the car is properly aligned (during which the tech should look for and find any signs of other problems in the steering/suspension areas).

When the wheels/tires were balanced a good tech will check for excessive play at the wheel bearing. Even as a layman, I can't hardly resist when walking up to my car when it is on a lift going around the car grabbing each tire at first the top and then at the sides and checking for excess wheel bearing play, any play of the tie rods, or other steering suspension component play, any play in fact.

In case this wasn't done when the wheels/tires were balanced you can certainly do it but the car should be safely/securely in the air with ideally all 4 wheels/tires off the ground. Be sure the transmission is in neutral and the parking brake is not set. You have 4 wheels to check. Chances are if a wheel bearing is bad only one will be bad so you have 3 good bearings and the play, or lack of play, the wheels with the good bearings exhibit to compare to the one wheel with the bad bearing.

When you check the front tires/wheels if you can have someone hold the opposite wheel so any movement you create arises from play not simply the steering gear moving.

Bad wheel bearings (unless the situation is severe) though are not known for vibration. They are known for being noisy and often times this noise can be affected by making sharp but safe turns -- swerving -- to see if one can affect the noise.

Sincerely,

Macster.

tbarcelo

Thanks for the input. I will look into rotor resurfacing. I'm not sure if I'm imagining this or not, but I feel like the hard braking shudder is getting worse. It may or may not be related to the vibration issue, but fixing it would certainly help the diagnosis.

I agree that wheel bearings don't seem likely. I have tried loading / unloading various corners while driving, and I don't detect any noticeable changes.

How common is it for strut mounts to wear? Is there a wearable bushing in our strut setup?

Macster

Sorry, but I can't be much help with strut mount wear. All I can say is generally (and this is stating the obvious) anyplace motion takes place wear can occur or component failure can occur and in either case this can allow undesireable motion or movement.

I'm pretty sure there are bushings or other types of bearings in the strut assembly to allow the portion that carries the wheel hub to move up and down and to allow the movement necessary to support steering motion.

Before I answered -- if what I posted can even be called that -- I did a read through of the strut section of the factory manual and there's not much more than drawings to go on.

Also, I've never had reason to research what strut wear items there are and this goes for strut bushings or other steering, suspension (front or rear) bushings since none of cars have yet required any attention in these areas.

And in my Porsche dealer visits I can't recall ever coming across a Turbo in for struct/suspension/steering component wear so I have no pics to share with you of these areas of these cars.

Sincerely,

Macster.

Macster

It just occured to me that you should closely examine the brake rotors, the holes to make sure they are clear. They can become filled up with brake dust (and rust dust).

In some cases -- my experience -- these holes can be cleared using at a DIY car wash using the car wash wand and putting the nozzle down close to the rotor. Avoid jamming the nozzle tip in to try to clear the holes hidden by the pad/calipers. Pull the car ahead a few feet to expose the covered holes for cleaning.

In more severe cases you may have to physically clean the holes running something through each one to knock the stuff out.

I bring this up because it just may be that some holes are filled and blocked and others aren't and depending upon how long this has been allowed to go on and how dense the material has become packed in the holes the rotors themselves might have developed an out of balance condition.

Odds are slim, I know, but just thought I'd mention it.

Sincerely,

Macster.

tbarcelo

I haven't done this recently, but I did check the rotors holes for dust / rust accumulation and they looked good. I'll double check on this one.

I'm planning to start by pulling the rear rotors and getting them checked. I'll keep you guys posted.

Thanks, as always, for the input.