At about 80 mph or so, when I brake, the steering wheel jiggles. Shouldn't it be rock solid while braking, from any speed? What's the most likely cause?

 

Yes it should be rock solid. It could be a warped brake rotor, or the rotor is uneven.

 

That happened in my then new 2006 Carrera S and the dealer replaced the rotors under warranty because of the extremely low miles due to it being a few months since I bought it. I'm not saying this will apply to you or that this is done in every case but it was so for me. Might be worth to try as, like texas355 wrote, it should be rock solid and likely due to a warped rotor.

 

Yeah. Mine is a month old with only 900 miles.

 

have you been tracking the car? Mine did that after a hard weekend at the track took it to the dealership they told me I warped the rotors. I ordered some new ones, I drove it for a while before changing the pads and rotors out. funny thing is it quit after a while?? they asked me if I had held the brakes on when they were hot (at the track) I didn't? I was trying to be careful as far as causing them to warp. I ordered mine from Sonnen Porsche, they had the best price on rotors, pads seemed about the same everywhere.

 

Mine is rock solid when I brake regardless of speed.

 

No tracking. No hard driving. Trying to obey the break in period.

 

I know on the Carrera S 997.1, the stock brake pads on the track can over heat. When they do, pad material sorta melts and transfers unevenly to the rotors causing high spots on the rotors. This causes the pedal to pulse and feel like warped rotors. When the brakes are cool and if the pad material isn't to heavy on the rotors, a couple of hard applications of the brakes can sometimes clean them off.

 

I also think in a recent issue of Excellence discussing track days, the article stressed the importance of NOT applying the parking brake after driving hard because the pads would possibly fuse to the rotors or possibly cause warpage as everything cooled.

 

The most common cause of pulsing brakes is improper bedding of the brake pads which deposits pad material unevenly on the surface of the rotors. They aren't warped. Making high speed stops and keeping the brake peddle depressed after the car comes to a stop is another cause which allows the pad material to transfer to rotor. It is the unever deposits that cause the pulsing you feel when you brake. Lots of technical articles on the subject. Re-bed the brakes and avoid keeping the brakes depressed once the car has come to a stop after high speed stops. The link below is informative.


http://www.mossmotors.com/SiteGraphi...rake_discs.htm

 

Yes.

What probably happened is the car sat on the lot and the rotors got rusty. (I use the amount of rust to help me determine how cars are moving off a lot when I am in the market for a car.)

The car was taken out for a test drive and the brakes were applied rather hard and the car brought to a stop. If the brakes weren't used a bit before this the rust is of course removed from the rotors during the hard stop.

The heat and the rust cause some kind of uneven pad material deposition to take place.

The result in the rotor at the place the hot pad (and rotor) were in contact has a different coefficient of friction.

The result in the brakes pulse.

It is highly unlikely this will cure itself. In some cases the rotors can be resurfaced.

In your case the car is new. I would take the car back request the brake behavior be addressed. Do not accept 'they all do that'. If you hear this then insist a similar car be used to take you on a test ride/drive so you can experienced this behavior in another car.

If the dealer balks then come back with that because of the pulsing when using the very safety critical brakes you have lost all enjoyment of the car.

To address this while the rotors could be resurfaced -- it is unlikely the dealer has the facilities to do this -- my WAG is the rotors will be replaced. The pads will probably be reused.

The 'new' brakes will or should be bedded in.

Oh, always when you wash the car be sure to take the car out and drive it enough use the brakes enough to get them hot enough to dry the brakes and keep the rusting to a minimum.

If you have to leave the car outside in the rain always try to use the brakes to scrub off any rust. Avoid bringing the car to a stop and leaving the brakes applied until you have used the brakes enough slowing the car to remove any rust that was present.

With a bit of care the brakes should stop the car smoothly and quickly at 600 miles, 6000 miles, even 60,000 miles, or more. (My 03 Turbo now has over 85K miles on its original brake hardware and the brakes still stop the car on a dime -- from sometimes considerable speed -- and without any drama.)

Sincerely,

Macster.

 

It sounds like a pad material transfer issue. If so a few medium/firm cycles from 65-70 mph to 20-25 mph may eliminate the problem.

 

Thank you. I'll read the article later. I haven't done anything that would be considered even near hard driving but I'll see what they have to say.

 

Thank you Macster, but the car was brand new when I received it. It was special ordered, went straight form Porsche to the Dealer to me.

 

if a few hard stops don't cure it the dealer will