Hi all.

My car has a vibration that starts to become noticeable at around 110 - 120mph, and steadily gets worse to the point where at 140mph it's very pronounced and I don't feel able to go faster.

1. Is this likely to be wheels that need balancing? What else could it be?
2. Can any tyre place do it competently for a Pcar at those speeds or do I need to find a real specialist?
3. Can anyone recommend a good place in Surrey (UK) that can be trusted?

TIA

 

Greg --

I had a very similar problem with my 78 930; around 110 it got a bit hinky and around 140 it required constant steering corrections. A 4-wheel balance & alignment fixed it all and now she stays where I point her at any speed.

Depending upon what tyres (notice the Anglo-spelling; who says Yanks aren't considerate?) you've got and how long the car has had between drives, the tyres could develop flat spots that would destabilize the car at high speeds. These flat spots usually work themselves out in a couple hundred miles, though -- and if they're not severe, you might not really notice them until you get into three-digit (mph) velocity.

Finally, if the suspension or chassis has been damaged, even slightly, obviously you're going to have issues; which issues will become at least aritmetically more pronounced at higher rates of speed.

If you can find a Porsche specialist, obviously that's what I'd recommend (though they're certainly not foolproof, as many of our Rennlist brethren can testify to). But, at the end of the day, wheel balancing and alignment are not rocket science, so a good competent shop that regularly handles performance cars ought to suffice. I'm of no help in Surrey, unfortunately, but check your local porsche club guys and look around for guys that regularly race/gymkhana/autocross.

Best regards and good luck.

JP

 

Dear Greg,
Wheel balance issues alone normally show themselves at much lower speeds. You have something about to fail under stress. Worn components. I highly recommend based on the other stories you have posted about your Turbo that you get the front end inspected. You had a cracked wishbone at one time I believe. I think you still have some structural issues. A "Proper" full all wheel alingment to the Porsche specs may show up the failure. Normally worn or failed steering/suspension components will not allow a correct wheel alignment. Just happened to me. I have a worn steering arm which will be replaced next tuesday.
An experienced mechanic should be able to deal with this issue during the alignment. As for a workshop I thought you had a good place. The only people I know who can be trusted are up North. Phil Hindley and his company.
Ciao,
Adrian
911C4

PS: Tyre issues as well should show up much earlier in speeds. Circa 60-80mph for you in England.

 

JP - thanks. I was wondering about flat spots etc since the car had sat in a dealer showroom for 6 months. BTW I did notice the correct spelling of tyres but if you want full points you'd have to use "destabilise" instead of "destabilize"..

Adrian -
So you don't think it's likely to be balance. Interesting... in a bad way, but interesting...

Thanks..

It seems every time I start to get interested in the car again it finds something else to throw in my face..

 

Hi Greg,

I'd agree with Adrian on the wheel balance issues, normally shows up around 60mph. I can highly recommend Tognola Engineering if you need an alignment check, they are in Montagu Road, Datchet, Berks, call Peter Tognola on 01753 545053. Their alignment equipment is as good as it gets (there was an article about the setup at Tognola in the August '99 issue of 911 & Porsche World) and Peter can handle any problems you might find.

 

You might want to visit you tecnicians in case it could either be wheel alignment or component issues, or someone who can cater for both. I think that JZ do but they are somewhat far from you.

 

Dear Greg,
I do not think it is a wheel balance issue nor a flat tyre spots issue. You are going too fast. They woul dhave shown themselves much earlier. Flat spots on tyres can be felt at very low speeds.
Th eonly tyre issue I could possibly think off and this is a wild step, maybe the sidewalls are starting to roll or distort on the wheel. Maybe the tyres are slightly too wide for the wheels. I very much doubt this but it might be worth checking. I still reckon it is a worn component in the steering or wheel suspension,
Ciao,
Adrian
911C4

 

Greg,
Try GT-One in Chertsey. They do an excellent job of balancing and alignment - and they will check things out before they start the alignment, since there is no point doing it if there is clearly something else wrong. I just had mine aligned there - and sadly, they found a couple of things wrong with mine before they started.

Dave
90 C4

 

Thanks for the replies.

The car has actually been both to GTOne and to JZ Machtech recently - the latter to redo the alignment (they were the ones that found the rear wheels had been set to toe-out instead of toe-in). GTOne carried out a PPI and the only related thing they flagged was the worn wishbone which was replaced before JZM saw the car. JZM test drove the car and didn't report anything unusual.. then again I didn't specifically ask them to spend lots of my money trying to find things wrong with the suspension... though you'd hope if they thought something was odd they'd report it.

>sigh<

Maybe I do need to take it back yet *again*...

 

Dear Greg,
I am sure they did not test drive at the speeds you are reporting either. Maybe you could do a run on four wheel rolling road and they maybe able to see the problem. It woul dnot surprise me to find it is related to the worn wishbone issue. Was the new wishbone correctly installed. Are the all the bushes okay?
Ciao,
Adrian
911C4

 

Hi Adrian.

Supposedly they did test at 120mph plus - because that's the sort of speed where I had cornering issues before they re-did the alignment. Their technical director told me that he had personally tested the car at 120mph plus (after the alignment) and thought it now felt fine.

AFAIK the new wishbone was fitted correctly but what do I know?? I guess the best thing is to take it back there. I think they do know what they're doing. They are a dealer for Roock (sp?) suspension so hopefully they know a bit about it..

 

OK, well, I had a pleasant surprise.
Talking to JZ Machtech they thought it could still be wheel balance, even though it's only noticeable at high speeds. So I took it to Micheldever this morning to have all 4 wheels balanced just on the off chance it might help - and the vibration has gone!

>phew<