Uneven Suspension - 2005 c2s tip with PASM

[achua]

Hi,

I've been through the posts and the topic that best describes it is found in the 996 section but could find nothing similar in the 997 section which led to a few questions. More on that further down:

I've got a UK version of a 2005 c2s tip with PASM but I now reside in the tropics where average temperature are about 30 degrees C all year round. I've owned it for about 6 months now and realise that the right rear suspension is about 1cm lower than the left rear and about 1cm lower than the front. Measurements were taken from the floor to the top of the wheel arch. Although this is not the way that Porsche recommends, it is the best I could manage under the circumstances. Looking at the car from both the front and the rear while it's stationary does show quite a visible list.

The car drives fine. It does not pull to any side but does roll a little more on the right when taking corners. Also, when taking speed bumps, the dampening effect of the shocks don't feel very even with the right rear feeling a little more sluggish. The car has only done about 18000 km. Low for one this age and certainly one of the main reasons why I bought it in the first place so a worn suspension on a car that has hardly been driven is a little bit suspect. I recently changed both front springs as one of the coils was slightly bent and was causing some noise from the steering when you rotated the wheel both when driving and when stationary. So the questions are:

1) Could it be a problem with the chassis? If not, what could cause the suspension to wear like that in a car that's hardly been driven?

2) Is it the shocks in the rear that are worn? In which case should I replace all four or just the rear pair?

3) Do the rear springs need replacing? Do the shocks make any difference in ride height?

4) What is the approximate cost of parts if I replaced them with standard Porsche parts for that model year?

While it doesn't seem to affect useability of the car in the short term, the car doesn't seem "whole" visually because of the list to the right and the difference in dampening action is just a niggling irritation that spoils the enjoyment of the car as a whole <_< . Appreciate anybody's input and thanks in advance.

[dphatch]

Don't think the front springs would cause this condition in the back. Not sure I've ever heard of a spring getting bent. Sounds like previous owner hit something substantial with front wheels. Curb maybe. Any evidence of other damage in the front. Shocks aren't holding anything up, springs do all the heavy lifting. Might be worth having your mechanic take a look before you spend any money replacing stuff. He can put the car on a lift and check all possible causes. Maybe cheaper in the long run.

[achua]

Don't think the front springs would cause this condition in the back. Not sure I've ever heard of a spring getting bent. Sounds like previous owner hit something substantial with front wheels. Curb maybe. Any evidence of other damage in the front. Shocks aren't holding anything up, springs do all the heavy lifting. Might be worth having your mechanic take a look before you spend any money replacing stuff. He can put the car on a lift and check all possible causes. Maybe cheaper in the long run.

The mechanic did check and the only issue was the front spring was a little bent but that was replaced and the front was fine after that but the rear suspension was feeling a little odd. Brought it back to mechanic and he said he checked the both coil springs in the rear and that the heights were equal and they were the correct parts. All four shocks also checked out ok but all he said was they weren't leaking oil so they must be fine. Floor to top of wheel arch measurements for front two are more or less equal at 69cm the right rear measurement was 70cm and the left rear was 71cm. So if the springs heights are not the issue, what else could be causing this imbalance?

[PAULSPEED]

I would replace the rear springs. Sounds like the previous owner

drove the car off a loading dock and bent the front spring.

The only way to test the rear springs is to remove them

and put them on a machine for testing. Replacing

them is the way to go.

Paul

[achua]

Thanks for the quick reply. I had the rear springs removed and heights compared (placed on an even surface) and they were equal. Which suggests that it may not be the springs fault. Could one of the rear springs have fatigued earlier than the other in which case the visual test wouldn't pick out the softer spring.

[PAULSPEED]

Race shops put springs on computer tester

to check them. Something tells me that a visual

is noy enough.

Paul

[berty987]

The springs sit in the PASM dampers with a specific location. The springs should be progressive and have the same compression when loaded. You could simply change the spring from one damper to the other or swap the complete strut from one side of the car to the other to prove this point. PASM dampers are not unknown to fail, they can fail internally without any outward signs. This was the case on my 2005 MY boxster , also fitted with PASM. The dampers were tested on a dynamic rig by Bilstein UK , this showed an irregular response in damping performance. I would advise replacing both dampers at the same time , especially on a car this age. The new damper is probably at least 4 revisions in part number from the original , suggesting a certain amount of upgrading by the supplier. I dont think its unreasonable to suggest that the broken spring would not only unduly load the damper on the front , but would also load to corresponding damper on the opposite rear side too. The PASM dampers have both sport and normal settings with adjustments in each mode. With the ignition "off " , the damper reverts to the sport mode in the stiffest setting , its therefore difficult to diagnose a faulty damper without a test rig when its disconnected from the car.

A couple of other things to consider

1 The anti roll bar, is it possible this has been twisted or the supports are loose ? This could cause the uneven poise of the car .

2 Each PASM damper also has an additional support spring , this is a rubber bush that sits on top of the damper rod, are these in good condition ? Part number 997 333 105 01

A PASM damper costs about 300 Uk pounds EACH ! There are no alternatives unless you buy the PSS9 dampers for PASM cars (also made by bilstein) as a complete kit. The dampers cannot be purchased outside of the Porsche network as Bilstein have a supplier agreement (this is worldwide) with porsche.

Springes will be cheaper to replace so check the problem is genuinely with the damper by swapping springs and location from one side to another.

Edited January 7, 2010 by berty987

[achua]

Thanks berty987 for the detailed reply. Have done what you suggested and that was to swap the entire struts right to left and there was still a noticeable ride height difference of about 10mm between left and right rear while the front was about 10mm lower than the lower of the two in the rear. In short, not much change after swapping struts. So i'm beginning to suspect chassis issues which would be very depressing.

The car does roll signifcantly more on the right than left without PASM in sport mode though...could this also be a problem with the chassis?

[berty987]

You mentioned a broken spring on the front, when both springs were replaced on the front as a pair , was the geometry re set ? A twisted chassis is quite severe, but I know of a cayenne that had similar issues , apparently on the cayenne there are spacers on the struts to ensure all four wheels have the same loading. Sounds like you need to talk to a suspension specialist , I would suggest a call to center gravity who are porsche suspension specilaists , here in the Uk. Though they may not be able to do the work for you (you are overseas) Chris Franklin the proprietor may be able to give you some pointers of what else to check. If the chassis was bent I'd expect evidence of a repair and some unequal shut lines or panel gaps.