03996

Above 75mph......I get a vibration that feels like it's coming through the seats. Not rev related, definitely road speed related.

Took the dealer tech guy out for a ride, he felt it and said he thought it was coming from the front tires. Checked the balancing and they were spot on. There is some slight odd wear on the edges of each front tire but, again, very slight. Alignment has been checked and is good.

Now, everything I've ever believed tells me that anything being felt through the seat or the back of the seat, is typically coming from the rear of the car. Both rear tires are new (PS2) and anyway, the vibration was there before they were fitted. Also had rear wheels checked for any bends.......nothing and checked twice.

I'm left with the drive shafts but again, dealer says they are ok!

Any ideas folks?

Best Regards

Les.

Revn29k00

Could this be caused by worn motor mounts? Are one of your exhaust tips lower than the other? I thought I had read on here that vibration felt in the seats are do to worn motor mounts.

996pp

Hi Les
By any chance do you have wheel spacers on the car?
My other 996 before this one had spacers when i bought the car and i had the same problem until i took them off.

2003 Speed Yellow 996 aero kit
Art

03996

Don't know about the mounts but the exhaust tips look perfectly aligned.

Also, and this doesn't make me feel any better, I did a search on this topic and one guy on the 928 forum has been trying to track down this exact same problem for over a year!! Also, guys running GT3's have similar problems!

03996

No idea about the wheel spacers......other than removing the wheels to check it out, how would I know?

laz74

You should be able to see spacers without removing the wheels - check btwn the rotor hat and the wheel.

996pp

You dont have to remove the wheels (depending what type of rimps you have on). If you can see the brake disc's from the outside you should be able to see the spacers. There is a post on spacers on this forum with pics if you dont know what they look like. Usually the cheap universal ones will cause a vibration at higher speeds.

MOVENU

Based on my personal experience with vibration in different vehicles I had found that:
1) Alignment - if the alignment is off that causes vibrations. I took it to one
shop to get an alignment done and it still vibrated afterwards. Eventually
took it to a shop that specializes in alignments and I don't know what
they did differently but the vibration was greatly reduced after their
alignment. (this was with my 911)
2) Wheels not being properly balanced
3) Poor tires. I had a truck that would vibrate at high speeds because
because the tires had uneven wear and another time i HAD A
particular brand of tire that for whatever reason caused vibration
and could not be properly balanced (on my suv)
4) Damaged or unbalanced driveshaft. I had this issue on a chevy van
(damaged driveshaft) and on a 300zx (unbalanced driveshaft)
5) a bent or damaged wheel rim will also cause a vibration (had this
on a van)

Keep in mind just a small variation in a tire or rim will be enhanced by
the massive number of rotations at high speeds.

Invius

I have heard this complaint from a number of 996ers, and the solution usually seems to be casued/rectified by one of two things.

Mis-matched front and rear tires...I know you have PS9's on the rears, what are on the fronts?
And motor mounts, but usually the vibration with the motor mounts is felt at idle and speed, not just at high speed, which makes me think wheel related.

GL,

DS

Macster

FWIW, running only N rated and matched but sometimes "worn" tires at the front and new tires at the rear with my 02 Boxster I have experienced a mild vibration that feels like it is coming through the seat.

One time the front tires (but check the rear tires too!) were overinflated and not by more than a few psi over the called out inflation pressure.

Another time the balance job was questionable and a rebalance (done free on goodwill by my dealer) proved to be the solution to the vibration.

Also, the techs tell me that even if the car leaves with the tires balanced spot on as the tires wear they can go out of balance and sometimes a rebalance is required before (way before) the tires are due to be replaced on wear alone.

I run my front tires sometimes over 40K miles and a few times over 50K miles and while they are worn down they are not worn out but it is the amount of wear that can affect the balance.

(The techs tell me the Cayenne tires are the worst in this regard because the tires are so big.)

Even if the tires are not worn down and the balance job was good, look carefully at the wheels to see if you can spot a missing tire weight. They have been known to come off if one is particularly aggressive with high pressure wash water from a garden hose or from a wash wand at a DIY car wash.

Any abnormal tire wear suggests alignment (or strut) issues so you need to always keep that in the back of your mind.

But check tire pressures and consider a rebalance before an alignment.

Sincerely,

Macster.

Dennis C

You're right about this issue with Cayenne tires. They never make it to 40K miles though! I'm happy if I get 30K!

j_five

Did u ever get this fixed? I bought new tires, rebalanced them. But still the same.

DBJoe996

Any vibration coming from the car at that speed has to be running gear related. Aside from the tires, wheels, alignment and motor mount concerns which are very good advice to check, have you checked the front control arms for any worn bushings and rear struts...how many miles on your car and have any of the suspension parts been replaced/upgraded? I've also had instances where a particular brand of tire just would not work well with a car. Replaced tires with a different brand and the problems went away. One way to isolate the problem might be to find a nice clear stretch of road, get the car up to speed and then take it out of gear and coast. If it still vibrates, it is tires, wheels, alignment, suspension component. If it doesn't then it is probably drive train related, i.e., drive shafts, motor mounts.

Macster

You must be sure of the quality of the balance.

Were the tires load force balanced?

Did the tech check each tire/wheel for any excessive run out?

Where the wheels mount is important too. A piece of dirt, a ding, anything that prevents the wheel from bolting on flat to the hub can cause a problem even if the wheel/tire are balanced perfectly.

Also, when the wheels are put on the tech should check there is no free play that the wheel and hub fit with no slop. Otherwise, the wheel can be off of center in relationship to the hub. I recall at least one case of winter wheels this was a problem. But aftermarket summer wheels, even Porsche wheels need to be checked for this possibility. You do not want to overlook anything for doing so can send you into more expensive areas and for naught.

Be sure the tire pressures are ok. As I mentioned in an earlier post, overinflation I have found can cause a vague but real vibration that can have one thinking balance when it is nothing more than a few PSI of overpressure in the tires.

The tech should have checked this but be sure the tires are identical, and if unidirectional mounted in the right direction.

If you believe -- make that if you are sure -- that there is no balance, tire mounting, wheel mounting pressure explanation, then you have to consider alignment.

Now, I remember one owner who had something going on with his Porsche and all the usual and even unusual explanations were offered and dealt with.

Several times he took the car to his dealer and was assured the car's alignment was ok.

Finally, in desperation he took the car to another shop and the shop found the alignment was not ok. The dealer, I'm sorry to report, was lying that is telling him it had checked (again) the alignment and found it ok. Inexcusable behavior from a Porsche dealer. Just simply inexcusable.

Anyhow, at the alignment time the tech can check for other issues, like any suspension or any steering component that is bent, has a loose or damaged bushing, is showing any signs of any issues in the bushing area. He can check the engine and transmission mounts too.

On a side note whenever a car has its drive shaft or axles shafts removed their current position in relationship to the mounting flanges must be marked so they can be installed with the same relationship. I mention this in case the shafts have been out of the car to replace the CV boots, or perform some other work.

You must get your money's worth from the alignment. Not only must the car come off the rack properly aligned -- get before and after numbers printout! -- but it must come off the rack with the tech's stamp of approval, with the techs's assurances that nothing else is wrong. No alignment will cure a bad suspension/steering bushing.

D6lc

I have a similar issue with my car:
No vibration before winter, car in great condition with new engine mounts.

Over winter fitted new MOW 030 suspension, all new control arms and bushes, ECS 8mm spacers at the front. New wheel bearings all round.

Drove the car 100 miles to settle the suspension, during that time had a vibration at around 75mph.

So last week had the car correctly aligned and all wheels balanced, the car drives better now the toe is correct, but it seems the vibration is still there. I haven’t really had a chance to drive the car much, i.e. ensure the sumi’s I have fitted run enough to get the flat spots out, which they are pretty bad for.

The spacers seemed good quality with tight fitting centering rings, next I will take them off to see if it makes any difference, after that it’s back to the shop that did the alignment & balance!