Vibration through car at high speeds > 70mph

[Evansmr]

I have a Jaguar S type 2.7 diesel registered in January 2006

It runs sweetly and quietly up to about 70mph but beyond that the car starts to vibrate. The steering wheel does not oscillate like it can when wheels are out of balance but you can feel vibration in the steering wheel, as you can through the seat, when eth car is travelling at about 80mph and above.

I have had new tires fitted recently on the front and tracking and balancing all round but this has not changed anything.

There are no knocks (“bonks and thonks”) from the suspension when going over bumps or potholes.

The car has touring suspension but don’t know if that is relevant.

Any views would be welcome

Thanks



Mike

[J44EAG]

Mike,

I had exactly the same thing on a V8 530i BMW.

A front damper was shot and what was happening was that the car at a certain speed generated a resonant frequency from the road spring. With the damper having little or no damping ability, the spring occilated at its own natural frequency and the car became most unpleasant to drive. Wheels were well balanced. The problem is not unusual or unheard of. A new damper fixed the problem.

All things being equal, there is little else that can cause the problem you discribe.

I have a damper on the front of J44EAG that showed slight signs of oil leakage when I changed the cruising spec road springs for an Adamesh uprated, lowered set at Christmas. The car on its old cruising springs, which were rather softer than the new springs, had just started to exibit the fault that you describe. The harder new springs have a different frequency to the old ones. I had planned to change the dampers at a later date when funds permitted. When I changed the springs, I noticed a slight oil weap on the damper rod oil seal. Knowing what occured on the BMW, the discovery came as no suprise. For the time being, I am not experiencing any vibration, but will have to address the problem if it begins to reoccur. The situation is holding its own for the time being.

On the cards now is a damper change to sports gas Bilstein units which as I remember, I found at best price on the net for £148 a piece from motorsportworld. Other than Jag Boge OE units, I believe that there are not many other alternatives other than Bilstein. That is what I shall be fitting later this year. Top notch manufacturer.

Try alsoEuro car parts and other internet suppliers. Cheapest by far compared with High Street prices. Avoid secondhand dampers like the plague!

In the forthcoming April 2010 magazine, I have an article being published on the S-Forum pages. With illustrations, it discribes how to change springs and, or dampers on an S. That might be useful to you.

Remember, dampers MUST be replaced in matched pairs. Unsafe otherwise.

Give me a call or e-mail me for further info, if you need to.

Mike Kennedy. S-type Forum Co-ordinator.

[Evansmr]

What you describe sounds plausible. I had a feeling that the wheels were vibrating in the vertical plane and had wondered if the wheels were out of circle but thought if this were the case then I would have had vibration to a lesser degree at lower speeds.

Certainly a fault with dampers would allow the wheels to vibrate in a vertical plane at a resonant frequency.

I will have them looked at


Thanks

[J44EAG]

My pleasure.

Also worth looking at ball joints top and bottom, but this is very unlikely to be the problem.

Sometimes tyres do go out of round or develop flat spots. Just jack the car untill a tyre is kissing the ground. Get down with your eye at floor level and rotate each wheel in turn.

Undignified, it is true, but at least you would see any high or low spots on the tyre.

Worn damper bushes just clunk. Anti roll bar bushes "bonk- thonk" as you discribe.

Still believe this is a duff damper.

Let me know what you discover please.

Mike

[Evansmr]

I took the car to Jaguar Racing Green Cars in Ash Vale with the full intention of changing shock absorbers, They firstly used a sophisticated balance machine (Hunter 5700) which could also tell if tyres were faulty by measuring variations in road force. The found that the OSR wheel had 100 gms too much balance weight (thanks to ATS tyres!). After this the car has run brilliantly. They checked bushes and shocks and all was ok.

I had just had fitted two new Pirellis fitted on the front at the time of the car’s service with the main dealer. The old tyres were badly worn due to poor tracking realignment (thanks to ATS again!). This Hunter 5700 machine was able to show that one of the new Pirellis had a variation in road force values suggesting something like a variation in wall stiffness of the tyre.

I was very impressed with Racing Green Cars and will for all future tyre changes use them because of the skill in correctly balancing wheels and because of the equipment they use.

[J44EAG]

A lesson for us all.

Just goes to show how sensitive to balance our cars are. Glad you got it sorted.

Full marks to Racing Green. They know their business when it comes to Jaguars. Thanks for letting us know that they have such a sophisticated piece of test gear and that you are pleased with their service.

So at the end of the day it came down to wheel balance. I`ve lost count of the times that David marks philosophy comes into play. "Start with the basics first". How true those words were in this case.

Perhaps the most worrying aspect is that ATS are not balancing correctly. Have you had a word with them about your problem? Seems to me they should be informed if only to get their modus operandi sorted out.

Mike