AspenSTI2010

Hi Guys, no bit the bullet and bought my first 911, a 2003 C4S, 6spd.
I had a PPI done, the only two things they found were a slight fray in the belt, which they replaced and that the brakes both front and rear would need replacing fairly soon.
I've noticed over rough roads, going over bumps and cracks the car still tracks straight but the steering wheel will shake (similar to that of turning slightly).
It seems to be worse the faster I go, 70mph it vibrates or shakes more vs 50mph vs 30 mph over the same stretch of road.
I checked the tire pressure and there was 35 in the drivers and 32 in the passenger. i set all 4 corners to 32 and did the runs again, seemed a little better but still quite prominent. I then put 100lbs in the front cargo area and it seemed to be worse.
I've had the front of the car raised and looked for play in the Tie rods, but doesn't seem to be any.
There seems to be a slight creek at very slow speeds (parking lot) when turning the car, more so perhaps to the right.
car tracks straight, doesn't shimmer or shake under hard breaking either.
Tires were new on the car when i purchased them.
Any ideas?


Turns out it was a worn out front passsenger shock. I had new Bilstein Sport shocks put in at all 4 corners and the alignment done and WOW
Now that's what I figured a porsche would handle like!

white99c2

is your car lowered, if it is your symptom sounds like a bump steer problem.

ivangene

+1 for bump steer

also what size tires/wheels.

could be a dead/leaking shock or someone changed springs and did not match the shocks

redridge

the slight creak while steering at low speed could be strut bearings..... what is your alignment setting? Stock?

nick49

You're under inflated, check the sticker on the car or look in the manual. You should be at about 36 F and at least 40 in R. If weighing the front made it worse, you may need more caster also your toe is more than likely off. Shimmy or wheel shake at speed is usually tire balance, if your pressures were off that much balancing is most likely off as well. Check for bent wheels too.

pongobaz

Tire pressure is way to low. Stock pressure for a C4S is 36 front, 44 rear. Try that first.

mglobe

How "new" were the tires when you got the car? Brand-new, or did they have some miles on them? I've seen this type of behavior from a bad tire.

AspenSTI2010

Hey Guys thanks for the advice, i'll try the new tire pressures. I have the stock turbo twist rims, tire size i think is stock, i'd have to run to the garage to check for sure.
Just took out a friends' 07' C4S, which is lowered, runs on 19" and it felt the same a but much less so. he said my car is either out of alignment or just could be that it's 8 years old.
My car is not lowered to my knowledge.
Will keep everyone posted.

vange_c4s

+1 tire pressure 36/44

Chaos

+2 I run 19's no problem

Macster

Slight belt fray could be due to an accessory drive having too much bearing play and the belt mistracking and rubbing on the side of a pulley of an accessory drive. It was a sharp (inner) edge on a serpentine belt that clued me (along with a few other things) an accessory drive had too much bearing play and I id'd the water pump.

Sincerely,

Macster.

Shark Attack

Had a simular issue after using fix-a-flat. Start simple go get them balanced

AspenSTI2010

Update: put the tires at the recommneded pressures=no better, no worse.

here's a little bit of video showing it, you can really see it at 38-42 seconds.



the car's steering wheel doesn't vibrate or shimmy or veer when the road is smooth or even a little rough, it's only during cracks across the road that the wheel will shimmy/shake back and forth a bit then go back to normal. it's very odd to me. did the same road in my STI and my mazda3 both at 70mph and nothing.
is this just bump steer? tie rods? steering rack?

will keep posted once i get the alignment done, but any other troubleshooting would be much appreciated.

mglobe

I wonder if one of your front shocks could be bad? If one side is underdamped relative to the other, it might give you something like you describe.

AspenSTI2010

Finally an update: Right passenger shock is shot. need to replace the fronts, quoted 4200 and change for two new struts, install and alignment (400 for alignment?!) and this was not at the dealership.