Vibrating rear suspension
07-26-2009, 05:03 PM
#1
Rennlist Member
Thread Starter
Vibrating rear suspension
I have a problem! 
When I reach 200 to 210 km/h, the rear of my car starts vibrating. It is mainly felt through the seat. The steering wheel stays steady as a rock.
When I let go of the accelerator, the vibration continues until the car slows down to 180 km/h. It seems as if it even vibrates a bit more when I get off the gas, as the weight transfers from the read to the front.
FYI, the car runs on OEM 17" rims 225 front, 255 rear with brand new Michelin Pilot Sport PS2 (less than 2000 km).
The suspension is Bilstein HD with H&R springs, which was installed last year. The car had the OEM M030 set-up from the factory, so the sway bars are of the sporty type.
Living in Switzerland, where the speed limits are strict and the penalties for speeding even stricter, it is near impossible to fix the problem. No mechanic will risk his license by taking the car for a test drive.
Instead, I decided to have someone check it out when I was driving through Germany on Friday. I was helped by a great bunch of people at Porsche in Bielefeld, and Vogt Tire and Suspension Specialists.
They discovered several issues on my car.
First of all, the 6 mm spacers I had on the rear had no center guidance. So, the rear wheels were basically only centered by the lugs. We immediately decided to ditch the spacers.
Secondly, 3 of my 4 newly mounted tires were not properly balanced.
Thirdly, the front shocks were loose!!! Apparently, the mechanic installing them did not torque them properly, which had caused them to induce slop in the front axle.
With all these issues sorted out, I returned to the autobahn in high spirits and anticipation of a great onwards trip to holidays in Denmark.
But the blody car still vibrates at 210 km/h!!!
What to do now??
The only thing I can think of is the rubber bearings of the rear sway bar.
Or maybe the mechanic who messed up the installation of the front shocks also botched something in the rear??
What do you think??
When I reach 200 to 210 km/h, the rear of my car starts vibrating. It is mainly felt through the seat. The steering wheel stays steady as a rock.
When I let go of the accelerator, the vibration continues until the car slows down to 180 km/h. It seems as if it even vibrates a bit more when I get off the gas, as the weight transfers from the read to the front.
FYI, the car runs on OEM 17" rims 225 front, 255 rear with brand new Michelin Pilot Sport PS2 (less than 2000 km).
The suspension is Bilstein HD with H&R springs, which was installed last year. The car had the OEM M030 set-up from the factory, so the sway bars are of the sporty type.
Living in Switzerland, where the speed limits are strict and the penalties for speeding even stricter, it is near impossible to fix the problem. No mechanic will risk his license by taking the car for a test drive.
Instead, I decided to have someone check it out when I was driving through Germany on Friday. I was helped by a great bunch of people at Porsche in Bielefeld, and Vogt Tire and Suspension Specialists.
They discovered several issues on my car.
First of all, the 6 mm spacers I had on the rear had no center guidance. So, the rear wheels were basically only centered by the lugs. We immediately decided to ditch the spacers.
Secondly, 3 of my 4 newly mounted tires were not properly balanced.
Thirdly, the front shocks were loose!!! Apparently, the mechanic installing them did not torque them properly, which had caused them to induce slop in the front axle.
With all these issues sorted out, I returned to the autobahn in high spirits and anticipation of a great onwards trip to holidays in Denmark.
But the blody car still vibrates at 210 km/h!!!
What to do now??
The only thing I can think of is the rubber bearings of the rear sway bar.
Or maybe the mechanic who messed up the installation of the front shocks also botched something in the rear??
What do you think??
07-26-2009, 05:10 PM
#2
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This may be a "way out from left field" response, but I sometimes have crazy ideas to try to solve problems. I'm sure someone will follow my post with a much more logical approach to finding the problem 
Theoretically, you could mount a mini lipstick camera or something underneath the car, aimed at the suspension. Set it to record, drive till the vibration happens, then review the footage, you might be able to see what's happening, maybe not, just an idea from outside the box!
Here's an example of what I'm talking about:
http://www.youtube.com/watch?v=J8sAaSkHwsA
Theoretically, you could mount a mini lipstick camera or something underneath the car, aimed at the suspension. Set it to record, drive till the vibration happens, then review the footage, you might be able to see what's happening, maybe not, just an idea from outside the box!
Here's an example of what I'm talking about:
http://www.youtube.com/watch?v=J8sAaSkHwsA
07-26-2009, 06:11 PM
#3
"Secondly, 3 of my 4 newly mounted tires were not properly balanced."
At 200+kph I'd look at balance issues still. My previous 964 had exactly the same problem north of 110mph I'd get rear end vibration. Had them balanced many time, problem persisted. I took it to Tech9 who prep GT1/2 cars(Lamborghini) they balanced them - Perfect.
Also same problem with my 993, north of 120mph, rear vibration. In this case the fitters only did a static balance, turns out the rears were 40/50gms out - Now perfect.
At 200+kph I'd look at balance issues still. My previous 964 had exactly the same problem north of 110mph I'd get rear end vibration. Had them balanced many time, problem persisted. I took it to Tech9 who prep GT1/2 cars(Lamborghini) they balanced them - Perfect.
Also same problem with my 993, north of 120mph, rear vibration. In this case the fitters only did a static balance, turns out the rears were 40/50gms out - Now perfect.
07-26-2009, 06:47 PM
#6
RL Technical Advisor
Jens,
I would have the wheel balance checked again. Many balancers do not have hub-centric mounting collets and instead use a tapered cone that yields inconsistent results. We had to spend a LOT of money to find this out so now we have very precise and repeatable equipment. Its not common knowledge.
I would also recheck each & every bolt/nut in the rear suspension: control arms, shocks, etc. If the technician didn't check his work up front, you may still have some loose hardware in back.
After that, I'd closely inspect and check every rubber bushing in the control arms as I don't think worn swaybar bushings create a vibration.
Please let me know what you find.
I would have the wheel balance checked again. Many balancers do not have hub-centric mounting collets and instead use a tapered cone that yields inconsistent results. We had to spend a LOT of money to find this out so now we have very precise and repeatable equipment. Its not common knowledge.
I would also recheck each & every bolt/nut in the rear suspension: control arms, shocks, etc. If the technician didn't check his work up front, you may still have some loose hardware in back.
After that, I'd closely inspect and check every rubber bushing in the control arms as I don't think worn swaybar bushings create a vibration.
Please let me know what you find.
07-27-2009, 05:15 AM
#7
Rennlist Member
Thread Starter
Hi guys,
Many thanks for the feed-back.
I will get the car on a lift to have a look at the rear suspension myself.
And I will check which kind of balancing equipment was used in Bielefeld.
Next step is to make an appointment with a specialist in Germany, for my return from holidays in 3 weeks.
I will keep you posted.
Many thanks for the feed-back.
I will get the car on a lift to have a look at the rear suspension myself.
And I will check which kind of balancing equipment was used in Bielefeld.
Next step is to make an appointment with a specialist in Germany, for my return from holidays in 3 weeks.
I will keep you posted.
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07-27-2009, 05:50 AM
#8
Rennlist Member
Thread Starter
Hang on! I just realised something 
The guys in Germany forgot to make sure the anti-theft lug-nuts were located opposite the stem valve!
Maybe this is the culprit. I will put them where they belong right away.
Incidentally, I have always wondered whether this small detail could really have any effect on the handling of the car.
The difference in weight between the anti-theft nut and a normal one must be all but insignificant. Right?
The guys in Germany forgot to make sure the anti-theft lug-nuts were located opposite the stem valve!
Maybe this is the culprit. I will put them where they belong right away.
Incidentally, I have always wondered whether this small detail could really have any effect on the handling of the car.
The difference in weight between the anti-theft nut and a normal one must be all but insignificant. Right?
07-27-2009, 08:20 AM
#9
Pro
Hello Jens,
I doubt the lug nut lock will throw any vibration into the car, regardless of where it sits. How about the wheel bearings or the half shaft? Are any of the 5 links loose or have play? Typically the lower most rearward link with the little plastic protector on it has problems. Check the rubber boots, are any of them torn where dirt could have entered the insides?
I had a similar problem once. I found out, that the whole rear end wasn't bolted down right. You might want to check all major mounting points. I do that on a regular bases as I live in Germany and always drive fast, as the conditions allow anyways. I even use torque seal so I can quickly check if anything has moved. I do that with the coil overs too!
Good luck and keep us posted.
Happy vacation.
Ed
I doubt the lug nut lock will throw any vibration into the car, regardless of where it sits. How about the wheel bearings or the half shaft? Are any of the 5 links loose or have play? Typically the lower most rearward link with the little plastic protector on it has problems. Check the rubber boots, are any of them torn where dirt could have entered the insides?
I had a similar problem once. I found out, that the whole rear end wasn't bolted down right. You might want to check all major mounting points. I do that on a regular bases as I live in Germany and always drive fast, as the conditions allow anyways. I even use torque seal so I can quickly check if anything has moved. I do that with the coil overs too!
Good luck and keep us posted.
Happy vacation.
Ed
08-31-2009, 03:09 PM
#10
Rennlist Member
Thread Starter
Hi guys,
Latest update.
During my stay in Denmark, I decided to change the engine mounts. I installed a set of RS items, sourced from Gert Carnewal.
As usual, Gert provided an excellent service, a good price and the mounts arrived in just 24 hours!
Sadly, after installing the mounts, the car still vibrates when going fast.
In order to get the issue solved once and for all, I decided to pop by Stuttgart on my way back to Switzerland. Where better to fix a Porsche?
The people at Porsche in Stuttgart were very helpful, and spent a great deal of time testing the car, the suspension and the tires. All with a smile, plenty of Porsche banter at the expense of Swiss mechanics... and they didn't even want me to pay!!
The diagnosis was a dying dual mass fly wheel.
Due to time constraints, they could not fit in an engine-out job right away so I headed on towards home in Switzerland.
My car is now due for the repair next week, and I pray for the best. And curse myself for not changing the flywheel, when the clutch was changed 2 years ago.
I will keep you posted.
Take care,
Jens
By the way, try driving across Germany in a 911, while being limited to 170 km/h. It gives a whole new meaning to the word "frustrating"!
Latest update.
During my stay in Denmark, I decided to change the engine mounts. I installed a set of RS items, sourced from Gert Carnewal.
As usual, Gert provided an excellent service, a good price and the mounts arrived in just 24 hours!
Sadly, after installing the mounts, the car still vibrates when going fast.
In order to get the issue solved once and for all, I decided to pop by Stuttgart on my way back to Switzerland. Where better to fix a Porsche?
The people at Porsche in Stuttgart were very helpful, and spent a great deal of time testing the car, the suspension and the tires. All with a smile, plenty of Porsche banter at the expense of Swiss mechanics... and they didn't even want me to pay!!
The diagnosis was a dying dual mass fly wheel.
Due to time constraints, they could not fit in an engine-out job right away so I headed on towards home in Switzerland.
My car is now due for the repair next week, and I pray for the best. And curse myself for not changing the flywheel, when the clutch was changed 2 years ago.
I will keep you posted.
Take care,
Jens
By the way, try driving across Germany in a 911, while being limited to 170 km/h. It gives a whole new meaning to the word "frustrating"!
08-31-2009, 06:16 PM
#13
Race Car
Glad to hear that at least you have now a resolution. Nothing worst that not knowing what could be causing the problem.
If you think cruising at 106mph is frustrating, come to the US and see what driving at 85mph feels like!
If you think cruising at 106mph is frustrating, come to the US and see what driving at 85mph feels like!
08-31-2009, 10:01 PM
#14
Rennlist Member
I had a similar problem and it turned out to be a bent rim. Do you have a second set of wheels you can install to see if that smooths things out?
I swapped wheels with a friend for a test. When I drove my car with his wheels and it was smooth, I was all smiles. That vibration had been driving me crazy..
Good luck...
I swapped wheels with a friend for a test. When I drove my car with his wheels and it was smooth, I was all smiles. That vibration had been driving me crazy..
Good luck...
09-01-2009, 09:37 AM
#15
Rennlist Member
I doubt the lug nut lock will throw any vibration into the car
to diagnose a vibration occuring at 200 kph and find the culprit to be the dual-mass flywheel?
i am really shocked, who else than stuttgart can diagnose this?
I mean really really hard to diagnose,
like revving up to 6000 rpm in neutral, and no vibration
but on road, vibraation at 200kph.
I will never forget this thread