ELJG

My recently acquired 95 GTS is suffering from vibrations felt through the steering wheel at 100 mph onwards. The tyres are Pirellis 6000 with approximately 7mm tread. Have had the tyres balanced twice (most recently by OPC), requesting they be balanced on the car and have also had the car geometry done (also by OPC) but no improvement.
I would be grateful for any and all suggestions.

Nicole

There is a good chance one of your front rims is bent. I've had this on my '91 S4 recently, and nothing really got rid of the vibration, except straightening the rim.

Is there a chance you could test drive the car with two loaner wheels in the front? Maybe the OPC (Old Porsche Centre?) has a pair that fit, or a fellow 928 owner in your vincity.

Where are you located? Maybe this board can help hook you up with some other local 928 enthusiasts.

Vilhuer

I bet OPC = Official Porsche Center and he's from UK. Many helpful locals in there who can assist I think.

AO

I aree with Nicole. Check your wheels for lateral and radial runout. ALso, check to see if there is a Hunter Road Force balancer in your area. Not only will it check the above runouts, but it will tell the installer how best to match the tire to the wheel.

Sharkbody

The road force way is best. You can high speed balance them till the cows come home but when the rubber meets the road, roundness rules.

ELJG

Thank you everyone. A prize for guessing U.K. (near London now, previously Venice, Fl.) and have posted this on local boards but I'm trying to get the most info I can (yes for the OPC too). The full car alignment was done on a Hunter machine.

Bill Ball

If they were balanced on the car or with road force, they should have noticed it if the rims were bent, the tires had a broken belt or were otherwise not round, but that needs to be checked. Nine times out of 10 this is a balance issue. As a simple test, you could swap wheels front to rear. If the front end wiggle persists, then examine balljoints and steering rack, although on a 95 GTS I wouldn't expect these parts to have issues unless high mileage and the symptoms aren't quite right.

ELJG

The car geometry was done first and then the balancing. Cannot swap fronts to rear - the rears are wider. Balljoints were checked (one was replaced), steering rack? (to look into). Mileage: 94000

Bill Ball

I know the rears are wider. You can swap them for a test. The rears should not hit the fenders in the front unless you go diving hard into a corner or your front ride height is way too low.

OK, 94k miles is high enough to definitely suspect other suspension components. The alignment tech should have checked them, although it requires lifting the car - a no-no prior to an alignment with these cars. Still, balljoint and rack tightness must be checked. However, the symptoms are usually vague steering and tramlining. Vibration still points to a balance or roundness issue.

ELJG

Bill,
Sounds like you hit the jackpot! I just thought that tramlining was a (no extra charge) feature of these cars so I have been trying to get used to it! And the steering itself is not rock solid (comparison is not particularly good since my other car is a VW Passat). I really don't know if the tech at the Porsche Center would have done anything beyond his brief - for instance I told them to replace the wipers: they did the front ones and never touched the rear! I guess I'll get them to check the rack, joints and wheel bearings. Thanks for that.

Bus

I'm sure you've probably eliminated this, but I've had two sets of P6000's now, one on my old Volvo S90, and a set currently on my '80 US 5speed... both sets have had a bad habit of flat spotting, almost overnight. The set on my Volvo would finally smooth out after getting warm... the set on my 928 I don't think ever will (because it sat for a couple of years undriven).

Nicole

I would not recommend swapping fronts and rears, unless you are on a track with no bumps. I once had a tire dealer accidentially mount the rears of my S4 on the front, and at the first bump they hit the front fender and scraped off all the rust protection.

If balancing does not help, I thiink the likelyhood of the rims being bent is very high. As to the tramlining, we all battle this in our higher mileage 928s, and it seems to get progressively worse with mileage. I'm still waiting tor the "easy way out" of this...

F4GIB

Not every "Porsche Center" is capable/desireous of repairing older cars like the 928. They think there is more money in new cars. Some dealers have sold off their factory tools (often on ebay) and many of the 928-trained mechanics have retired.

My tech (age 39 or so) has finally convinced his Dealership's management that he (and they) can make good money from his interest in older cars but it was an uphill battle. They "knew" from the dealer grapevine that there wasn't enough work until he convinced them to run, and look at, the actual numbers he had been producing. Better work plus some investment does yield more work (and profits), and so forth.

P. S. I had front-end vib at high-speeds on my 1995 GTS too. Bought 4 new tires and the problem disappeared. I'd strongly suspect the tires.

Herman K

Just sharing my tire/steering experience

I recently replaced my front tires and had an alignment done by a local alignment & brake specialist. The shop owner personally drives each car they work on before and after they complete the job and gives a year warranty on his work. When the work was completed (all in specs) he drove the car to test according to his standard procedures. When he came back he said the car had a slight pull to one side instead of being tramline as it should have been. He had has guys recheck and it all came out OK, he was not satisfied himself and mentioned to me that he suspected the tires and recommended that I would take the car back and swap the front tires on the rims. In order to back up his argument he went through the trouble of exchanging the right and left wheel and tire to demonstrate the effect this would have ( knowing that this would result in the tires being on the car in the reversed rotational direction but just to proof his point). And indeed when this was done the car was perfect. With this information I took it back to the tire store and insisted they remount the tires on the opposite rim in order to have the same effect with the right rotational direction. I now have done about 3000 miles and the car runs tramline. I would never have believed it if I would not have seen this for my self. Obviously these cars are very sensitive and any little thing that is out of spec. can cause a problem. I’m inclined to believe your problem is with your tires.

94 GTS 5 spd, 94K miles

Joe '87 S4

I have them also and you are right on - they flat spot almost overnight. It takes a few miles before they balance out.