993 Vibration at higher speeds

[jrgwilson]

Hi again,

On to my next problem!!!!

I have recently bought a 1996 C4 and am experiencing some vibration at higher speeds. I'm reasonably sure it's a new problem since I had my hollow spoke 18 inch wheels refurbished, but I can't be sure as I got them done almost straight after I bought the car (private sale) and hadn't done much motorway driving at that point.

The vibration is very predictable and starts nearly exactly at 80mph and continues at higher speeds. It doesn't appear to a revving issue as at higher revs through the gears there is nothing unusual. Also the vibration seems to manifest itself at the rear and there is nothing to suggest any problem at the front of the car (no feedback in the steering). I'm thinking the refurb on the rear wheels has left them unbalanced and or slightly incorrectly fitted. The guys who did them didn't do a great job to be honest. Not sure I trust them. Obviously I'm intending to get this checked. BUT, has anyone else had a problem similar to this, or is there anything else I should start thinking about? (I presume the 993 is generally a little more refined at higher speeds, mine is pretty exciting at +80mph right now!!)



Thanks

[herman maire]

I would check your rims and tires to be 100% they are NOT the problem.... take it to a good porsche shop, DONT TAKE IT TO THE SAME PLACE. I have been to a ton of shops who just plain SUCK when it comes to tire and rim balance... they just dont give a S%$t or there balance machine sucks.

Are your tires new? really cheap tires dont balance well SOMETIMES.

[jrgwilson]

Hi, thanks for getting back. Tyres look fine and are of decent quality. I'll definitely take the car to get the wheel re-balanced and get rims checked etc. I've also had it said that the refurb process can lead to sand and debris getting inside the wheel causing bad balancing. Like I said, I think the guys who did the refurb were pretty amateurish. Thanks, will let you know the solution (when i find it!!!)

[cjoenck]

The fact that the vibration starts at around 80mph points very strongly to wheel imbalance. When the wheel was refurbished, they might have knocked off one or more of the balancing weights on the rim. Get the wheels balanced and that will most likely solve your problem. The other options are not as pretty:
If someone overtorqued the lug nuts, you might be looking at a warped rotor. Another possibility is a worn wheel bearing. How many miles do you have on the car?

[jrgwilson]

Problem solved! Thanks everyone for your help. I had to buy four new shoes in the end but it's well worth it!! The old tyres had flat spots, plus the last rebalancing was very poorly done. Also the rears had nearly a litre of water sloshing around in each one?!! Also the car had signs of sitting around unused for long periods (pre my ownership) and this had made the rubber misshapen also. No wonder I had some serious vibration issues......

So four new Pirelli P zeros later and the car feels super slick and smooth, really excellent! Things to learn: 1) Low mileage cars could mean a lot of sitting around and that can make even tyres with plenty of tread out of shape. 2) Porsche wide wheels should be balanced with weights on both outer and inner edges (not in the middle) according to my experienced technician. 3) My old tyres looked in nice condition, but low miles doesn't tell the whole story, they were getting on for six years old and the rubber had degraded just through lifespan and not usage. Hope these pointers help. Cheers James

[24fps]

be careful who referbs yer hollows too... some have had sand in the wheels & broken/tweaked metal stems. just FYI

bol

[Groesbeck Hurricane]

I would suggest you have the wheel bearings cleaned and repacked, or have fun and do it yourself. A car that sat that long will sooner rather than later have wheel bearing issues.