2003 Porsche 911 Cab. 56k miles. Looking for guidance and / or ideas to resolve a slight front end wheel shimmy problem when traveling above 70 MPH and slight pulling/fading to the right. I purchase this car 3 months ago from a local Porsche dealership. Dealership has acknowledged this shimmy and they have been accommodating but they have not been able to resolve the problem. Car has new Continental 225/40 ZR 18 92 YMS on front and 285/30 ZR18 93 YMS on rear. Just recently had wheels Hunter Road Force balanced with left front at 12 lbs, right front at 5 lbs, left rear at 7 lbs and right rear at 21 lbs. Also had aligned; left front camber .08 & .05 toe, right front camber .14 & .08 toe, front total camber -.07 and toe .13. Rear left -1.34 camber and .22 toe, right rear camber -1.15 and toe .24. Total rear toe at .46 and thrust angle -.01. All other allighnment data is “……”. Dealer identified right rear wheel was bent and was sent out for repair and reinstalled before above adjustments. Dealer also substituted a complete set of balanced donor rims and tires to rule out issues, but car continued to have shimmy and fading with donor set.

 

this could be a number of things . worn suspension , tie rod ends or even a bad wheel bearing . have all these parts inspected

 

For a 911 Carrera narrow body, the alignment specs are:

Front
Toe: -1 deg 20' +/-30'
Camber: 0 deg +/- 15'
Caster: -8 deg. +/- 30'

Rear
Toe: +10' +/-5'
Camber: -1 deg 10' +/-15'

If the alignment was done by the dealer you should have received a print out that graphically depicts the 4 wheels/tires and the settings for toe, caster, camber and a couple of other settings or derived settings.

In your post I do not see caster. Caster is very important. Even if left and right caster values are within tolerance but still are close enough the car will have a tendency to pull one way or the other. IOWs, if one side has a caster value of 8.5 while the other side had a caster value of 7.5 I can assure you the car would pull towards the side with the 7.5 caster value. In fact I just checked and the max difference between left and right is 0 degs 40' or 0.667.

As a reference, last alignment my 03 Turbo received the caster was: 7 degs. 25' (left) and 7 degs 21' (right). In decimal degs/mins: 7.467 and 7.35. Early only the caster was identical. The fact it is not now is a sign of suspension bushing wear/aging I suspect.

Oh, before I forget 996 Turbo alignment numbers can differ from those for your car so these numbers are just to show you actual alignment numbers that my car received, how close (or not) the two sides were to each other and alignment numbers that I know did not result in the car manifesting any issues or premature or unusual tire wear.

For front toe, in decimal degs. and mins. front toe can be -1.3 +/- 0.5 or -0.8 to -1.8.

For your car toe is 0.05 (left) and 0.08 (right). Assuming the numbers are in decimal degs/mins there is too little toe and it is positive and the two sides are not in close enough agreement. By comparison my car's numbers: 0.033 and 0.05. (Note: The Turbo receives less front toe than your car does and it is positive: 0 degs 5' +/-5' or 0 to 0.083.) Your car's settings differ by 0.03 while mine differ by only 0.017.

In decimal degs. camber can be 0 +/- 15' or +0.25 to -0.25. With your car camber is 0.08 (left) and 0.14 (right), with a difference of 0.06. My Turbo: -0.05 and -0.116 for a difference of 0.066.

Rear toe is 0 degs. 10' +/- 5' or +0.167 +/- 0.083 or +0.250 to 0.084.

For your car toe is +0.22 (left) and +0.24 (right). For my car toe is 0.167 and 0.183. Your car has a good amount of toe out. Note our cars use toe out at the rear because the rear wheels tend to pull forward going down the road under engine power. I do not think the toe of your car's rear tires accounts for the wandering but it could result in uneven tire wear with the wear concentrated at the inner edges.

Total toe is 0.46. For my car is it 0 degs. 21' or 0.35. My car has less rear total toe then your car.

For rear camber, the specified range is -1 deg. 40' to -1 deg. 10' or in decimal: -1.665 to -1.167.

For your car rear camber is -1.34 and -1.15. For my car it is -1.516 and -1.55. Your car's rear camber is too little and the right side is out of spec.

In my opinion your car's alignment is not optimum and not really to spec. I would have this put right and see how the car drives afterwards.

Up to you but I believe you should insist on having the car aligned and you want a before and after printout of the car's alignment values. And before you accept the car insist on a test drive to verify for yourself the alignment feels right. Be sure you have a good route near the dealer so you can zip out and drive the car and compare to how it feels after the alignment to how it felt before the alignment.

Before you approach the dealer about an alignment, be sure tire pressures are ok. Too much tire pressure in the front tires can give rise to a vibration at higher speeds that sure feels like a tire balance problem. And I'm not taking about a huge overinflation condition either, but just a few psi. Be careful. Some cars have the recommended inflation pressures on a label on the inside of the gas cap door/lid but these pressures are for a fully loaded vehicle. Unless you are carrying four adults and their luggage you might want to drop the inflation pressures by say 2 or 3 psi. Be sure you use a quality air gage and get the pressures, whatever you settle on, these same left and right.

Still I do not think a few psi too much air pressure in the front (or rear) tires accounts of the wandering you report.

If you end up having the car aligned, show up with the car empty of junk (dead weight). If the car has a spare tire and tool kit be sure these are properly stowed. Fill up the gas tank.

Oh, be sure you request the steering wheel be centered.

 

Thank you very much for your post. I attached the report for your reference.

 

Did the dealer inspect ball joints and control arm bushings? My bet is on one of those.

 

maybe wheel bearings? appear normal when hand spinning but upon speed
they might tend to wander on the spindle

 

Did you check to see if this car has been in an accident. Or at least ran over something large to knock the steering out. At only 55000miles, there should be nothing wrong with bushings or any part of the steering. Or the car could have been owned by some **** for brains nutter who tried to improve the driving for track use and didn't know what the **** he was doing. That is my calculated guess. You say the front wheel was bent. Yeh they usually get bent if they hit something hard. Some other part of the steering is bent also. Get a Porsche Garage to check it out and suck up the loss. My guess is you got the PPI from the dealship which you bought the car. CORRECT? DUH. Toe this and toe that. Someone needs a swift toe up the **** in my opinion.

 

Front camber looks ok. Each wheel's setting is within tolerance and both are within the max. allowable difference between left and right.

Front caster is missing. This is troubling. Caster is a very important alignment setting. My info is the caster settings between the left and right wheels wants to be very close as too much difference can cause the car to pull to one side or the other. (Caster difference can be used to compensate for the car's tendency to "pull" from road crown. I prefer my car alignment not have any difference in caster. I prefer to "feel" the pull associated with road crown and have to steer to compensate. My reason is where I live/drive roads have varying amounts of crown and some lanes have the crown in the opposite direction so neutral caster is best for me. Caster is not used so much now as some cars (dare I say most?) come with no caster adjustment possible. Caster is "fixed".)

Front toe is ok. I initially had it as wrong but I got the settings for my Turbo mixed up with the setting of the narrow body Carrera model.

Toe is +0.083 +/- 0.083. Max. allowable difference left to right is 0.33.

Rear camber is while within spec still has considerable difference from side to side. The difference is not close to the max. allowable difference between sides, but imho the camber should be closer. Camber (at the front) is another setting that can be used to compensate for road crown. As with front caster, I prefer camber (front or rear) *not* be used to compensate for what road crown the tech imagines the car will encounter. My point is that a too big a difference in camber at the rear could account for some pulling.

Rear toe is ok.

What to do?

Well, it is not 100% certain a better alignment would help. However, there is still the question of what is the caster settings?

A good tech would go over the settings with you and assure you the settings should not account for the behavior. Especially since you brought the car in because of drivability complaint.

A good tech would certainly give the steering/suspension a thorough check for any loose bushings, signs of damage, etc.

BTW, this includes the bolts/studs holding the front (and rear) struts to the body. In some cases some of these have been known to break and the car can manifest symptoms you mentioned.