Number54

First is a rumbling when the car is in a hard turn. Seems like its coming from the tires, and the sound fills the cabin. I was running tires that have maybe 15 heat cycles, but they are street tires and still have good tread. They were slippery too. Could the tires be somehow dead?

Second is a twitch on throttle on/off. This even occurs on very light throttle on/off. It does not occur on braking, even very hard braking is stable.

Any ideas?

Thanks.

oh, and my GMG WC-GT cage developed an awful squeaking on the way back. I can't tell where it comes from. A passenger said it sounded like it was coming from near the window (perhaps the bar connecting the shock towers?). What's the solution? Grease every connection? Or WD-40 perhaps?

bobsan

assuming all wheel bolts are tight, rumbling could be wheel bearing.

twitch - is that an engine twitch or chassis twitch, need more detail

StevoUK

Could be rubber pick up from the track stuck to the tyres.

Number54

Thanks all.

Wheel bolts were all tight. Is there a way to check wheel bearings? The rumble is on hard turns, I can't reproduce it safely on the street.

The twitch is chassis, although brought on by throttle on/off. Once I've got a bit of throttle, everything is fine. Its when getting off the throttle completely, or getting onto throttle from zero throttle. There is basically a yaw to one side then the other. Its quick - a fraction of a second.

I can't say for sure its not rubber pickup, but I don't think so. I'm going just on the basis of other track events, I have never had this before. Also I had an instructor passenger and he didn't know what it was. His advice was to change all tires to something well known like Pilot Sports and see if the rumble comes back.

Thanks

LVDell

Two places I would check are bearings and LSD. Sounds more like bearings though.

Rubber pickup will be constant and a vibration like the wheels are out of balance.

DHI

Twitch and rumble may be related.
I say wheel bearing.
Jack up the car and see if there is any play when grabbing/rocking the tire at 9&3 o'clock and 12&6 o'clock.

mooty

if wheel bearing dead u may lose alignment this causing twitch under throttle. that happen to me

Hoosier_Daddy

+1.

To check the wheel bearing (at least initially), lift the suspected corner off the ground and with your hands first at 3 & 9 o'clock, then 12 and 6, check for play in the wheel/hub. If there is sufficient play, it *might* explain the slight twitch as that wheel's alignment may change (slightly) as the weight transfers on and off.

Can't be certain -- but it's a good place to start.

Good luck.

4porsh

I will throw some suggestions into the mix.

I would have your tech look into the Transmission Carrier Mount.
When the rubber wears out it makes noise only on hard turns at the track, could not make it happen on the street.
Also check diff, may be worn out.

http://www.suncoastparts.com/product...96_GT3_Chassis

Good luck,

Joe

996FLT6

Sounds like wheel bearings to me. Now your roll cage it may not be the cage itself. I had very nasty squeak on passenger side rear strut tower. I tried titening bolt but to no avail the thing kept squeaking. U should make sure Neway if the bolts are tite if it's like the rs clubsport it can squeak. My issue is the top hat inside rear strut cracked. I sprayed gobs of wd-40 on top of strut waited 30 minutes. Drove car no squeak. It maybe the top hat. Worse squeak of all squeaks I've heard sounds like an angry bird. Mike

himself

Does the rumbling sound like something rubbing? Are you running new size tires? Or spacers? Does it sound like it is coming from the front or rear?

-td

Number54

Thanks all. After spending some time on the car, I still can't figure out the issue. The wheels don't budge when testing the wheel bearings. One question though, does the handbrake affect this test on the rear wheels? I think I did it with the handbrake on

The only thing I saw was some buildup of tire gunk. See the pictures below. There was some buildup on the edge of the cup lip, and on the inside fender lining. Could this cause rumbling on hard turns? Should I replace the inner plastic lining that has peeled a bit? I've never seen this before.







I'm pretty close to just taking it to the shop to figure it out.

Thanks.

Number54

No it doesn't sound like rubbing to me. Although my front tires show a *tiny* bit of rub. Tires are standard size, stock wheels, and no spacers. The sound fills the cockpit, I can't tell if its front or rear unfortunately (plus the helmet doesn't help).

Thanks.

Number54

Some pics of the event:

Dervish

I got that rumble at Spa recently, no noise on straights but fast corners where you're more on the edge you get the rumble. Its just rubber pick up which hasn't been scrubbed at the edges. That's my guess and experience anyway...