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977 stability problem

  • 2009
  • 911 Carrera S
Mileage: 
44 000
Other
Virginia Beach, 
Virginia

Stability problems with my 2009 Carrera S.

Problem 1:

Driving a DE at Virginia International Raceways I encountered a stability problem in a very mild
turn on the Front Straight at 122 MPH.  The car began to Fish Tail and was very difficult to get
under control.  My instructor agreed that it was a car problem, not the driver.

Driving the back straight which hasn’t the slightest turn the car starts to feel unstable over 115. 
Two months earlier I drove this straight at 136 and the car felt rock solid stable.

Problem 2:

Mild braking while turning causes the brake pedal to vibrate, not at an ABS frequency of about
20 Hz. but at a few cycles/sec.  I believe the PASM is breaking a front wheel or two.  This can
cause the front tires to slide out as in under steer.

There is no problem with threshold braking.

Although I first encountered the problem on the track but I can recreate this if I take and exit just
a bit fast.

This problem does not seem to occur in the first five minuets of a run on the track but starts
about 10 minuets into the run and gets worse over time.

Other info:

The front rotors and pads and rear tires were change a couple of weeks before this track event.  

Connecting the car to a computer shows no error codes and the wheels all turn at the same rate
when driving straight. 

The angle sensor for the steering wheel is correctly calibrated.

Tire pressures have bee checked.

The brake fluid was changed in January 2014 as routine maintenance.

Monty O’Connor

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