GT3 Steers by itself? Not happy..can anyone help?

[daniel1]

I'm new to this site and new to Porsche ownership. I was recommended this site by a guy at "flat-6" forum as being a bit more technical?

So, hello, here is my problem.....can anyone help?

I recentely had the fortune to purchase a 1999 GT3 but I have encountered a handling trait that is very array. This is what happens:

At any speed/gear/rev combination(but most noticeable at 3-4000rpm), when I apply throttle the car veers to the right. When I lift off the throttle it veers left. I am very confident that it is not a tyre/brake problem and have had suggestions that it could be a front roll bar bush or wishbone fault. Furthermore it is definantly not my input on the wheel or road camber or crosswind/aquaplaning etc...

The rear LSD/axle makes a hollow grumbling noise at slow speed/tight corners. Is this normal or could it be part of the problem?

As you can appreciate, I am a bit cheesed off that the car has this fault as the handling was the major reason for the purchase. At the moment it is alarming to drive! It is a fabulous machine that I want fabulous again. Please, can anyone assist with my diagnosis so I can enjoy it again? The car is going to a dealer this weekend but if I could turn up with suggestions it would help things along.

Thanking you in advance.....great site by the way, look forward to future reading and hopefully contributing

Edited January 8, 2004 by daniel1

[KarlS]

You description of the symptoms and the noise would certainly make me suspicous of the LSD as the culprit. The easiest way I know of to check the LSD is to jack up one side of the rear of the car. If the wheel that is off the ground can easily be turned, the diff is open and has failed. If it is difficult to impossible to the turn the rear wheel, the locking action of the diff is still working and you may need to look else where for the problem.

Also, make sure you have the alignment check by a competent mechanic. It's possible that a variance in toe settings from one side of the car to the other could be causing this behavior.

Karl

[daniel1]

Guys, I don't know what to say! Just went to check tyre pressures to discover slow puncture in rear right (down to 25 psi). Not quite as embarassed as could be since I had cheecked pressure only two days before handling trait emerged. Had already ruled out tyres because of that. Thanks to you lot, I re-checked them and car is magical again!!!!!!!! Just shows what a sensitive beast this car is........

[clord]

Daniel....also see the thread in the GT3 board entitled "GT3 Steering Precision" that I started on 17 Sept. BTW, the LSD sounds you describe sound normal.

[grant]

An improper kinematic toe setting on the 993/996 cars also will cause the driving behavior you described (changing steering direction with throttle application or lift).

[viken]

An improper kinematic toe setting on the 993/996 cars also will cause the driving behavior you described (changing steering direction with throttle application or lift).

Grant,

FWIW, the 996 cars do not have a kinetic toe setting anymore.

[mds]

If the wheel that is off the ground can easily be turned, the diff is open and has failed.

Karl

Karl are you sure about this? The rear wheel on my car turns freely when lifted up, yet the diff seems to be working fine. I had my dealer check it this morning, and he said everything appears fine. His explanation is that the diff locks up only under torque and will freewheel otherwise. Do the wheels really lock on both of your cars?

Edited February 9, 2004 by mds

[mds]

Ok, I figured it out. If the transmission is in neutral, a lifted rear wheel will freewheel easily both directions. There is no torque to cause the LSD clutch to engage. With the transmission in gear, clutch out, engine off, there is an applied torque when you try to rotate the wheel, and after a small rotation the LSD clutch engages and so there is no further freewheeling. So check both wheels, forward and backwards, with the car in gear and parking brake released of course. :-)

Edited February 11, 2004 by mds