shaking and sawtooth on rear tyres

[marksawtell]

Hello there and thanks in advance for any help!

I have a 996, 1999 model c2

I started noticing a rumbilng noise when driving and suspected one of the front wheel bearings as the rear ones had been replaced about a year a go and being a high mileage car thought they were due for replacement. I replaced the two front wheel bearings and the two drop links at the front as these are prone to wear. The noise hadnt gones so I went and got all wheels balanced and it was at this point the tyre shop pointed out I had 'sawtooth' on the outer edges of both rear tyres.

With the rear tyres replaced the rumbing had gone but i can still detect a faint wobbling which is more noticeable between 40-80mph. im guessing this is what has caused the tyres to 'sawtooth' over a period of time. I have never had sawtooth on any previous tyres. (for those that dont know 'sawtooth' is where if you were the run your hand round the tyre, it feels as if the the tyre tread is stepped)

Anybody got any ideas as to why im still getting the shaking after all wheels balanced and whats likely to be the cause of the sawtooth although i think the shaking and sawtooth are related.

Once again any help will be greatly appreciated.

Merry xmas btw!

Regards

Mark

[Loren]

May seem simple but make sure the wheel lug bolts are tightened to spec. I mention this as I have seen loose lug bolts cause the same symptoms.

[marksawtell]

May seem simple but make sure the wheel lug bolts are tightened to spec. I mention this as I have seen loose lug bolts cause the same symptoms.

HI Loren, thnaks for your quick response, its definately not that. The wobble was there before the tyre change and still there afterwards. I just went out and double checked and they are tighter than usual, drove it again and still there...

[logray]

Have you used a tread gauge on the tires? If they are nearing the limit, perhaps it is time to replace them.

Are they worn unevenly? Tires that are worn unevenly can have these types of characteristics

The lug nuts should not be overtightened, rather they should be torqued to exactly 96 ft lbs in a star pattern.

[marksawtell]

Have you used a tread gauge on the tires? If they are nearing the limit, perhaps it is time to replace them.

Are they worn unevenly? Tires that are worn unevenly can have these types of characteristics

The lug nuts should not be overtightened, rather they should be torqued to exactly 96 ft lbs in a star pattern.

The tread gauage on the original tyres was good, the tyres were only two months old, yet the sawtooth had occured in this time. Tyres also didnt seem to be worn unevenly. i am concerned it will do the same to the new set of tyres i have. I dont drive eratic and i am still convinced the low rumbling/shaking i am getting is the factor to the sawtooth. I read somewhere a dodgy shock absorber could be the reason for sawtooth, but its very hard on the back of the porsche to tell if a shock is gone. it says push on the back of the wheel arch and see how many times the shock bounces. It took all my strength to push the back down and it seemed just to return to the position without any bounce.

I just know the shaking/rumble wasnt there before.

Any other ideas???

[logray]

Has the car been aligned recently? Is there any damage or worn bushings on the suspension components?

[marksawtell]

Has the car been aligned recently? Is there any damage or worn bushings on the suspension components?

Hi logray, no it hasn't been aligned and that was my next step if there weren't any other suggestions. All the bushes were checked by a mechanic and said to be fine.

[rattles]

I had exactly the same problem with my 99 c2, it turned out to be the real wheel alignment. It was incorrect from the factory. The dealer could not find the problem but a very good independant workshop took it for a drive at around 20,000kms, immediately said it was the rear wheel alignment.

After adjustment the noise dropped a lot but by then the tyres had been ''cupped'' on the inner edges to the point they needed replacement, the new tyres cured the noise problem completely. From memory the wheels were toeing out around 3mm

Edited December 22, 2011 by rattles

[marksawtell]

Thanks everyone for helping and rattles it was exactly what you said above! :-)