Brake fade question
 

Since the day I bought my car it has always had a weird braking quirk. I posted about it a while back. I thought I would post again since I should probably take the car in. When ever I am braking and I hit a bump in the road the brakes feel like they give and let go, it is a very strange feeling. The only thing I can compare it to is brake fade.

Today coming into work I was following an AS C4S ( BTW Great looking car if you are on here) when I was coming off of a big sweeping offramp ( Ave. of the arts and I5 ) I was doing prob 85 and then braking as there is a light at the end of the offramp. The brakes felt real jerky, it was a very uneasy feeling.


So what do you guys think? Warped rotors? Bad bleed job? ABS acting up? or ???

I am puzzled what ever it is I am going to take the car in.

eric,
i have had the same incidents, but it was over stutter bumps or gravel. if it was a smooth surface i would believe it was the abs and maybe a combination of bubbles in your brake line. especially if you have had your calipers removed at one point.

Wouldn't the bumps in the road cause 1 or more of the wheels to lose traction momentarily (airborne?) and thus cause the PSM to interfere with braking etc? not sure though

Same thing here...Braking over speedbumps cause it to shudder or something?

BTW, I don't have PSM so that can't be it.

Eric -

It's hard to describe...but does it almost feel like you are going over rocks when braking? A metallic pulse?

Same thing here meaning you have the same problem? or you are thinking it is PSM? I will shut PSM off tonight... but that still does not explain the shudder problem that I experienced while braking around the sweeping off ramp.

I don't know how else to descibe it other then it is kinf of like brake fade like you are driving a big truck coming down a big hill. But then it will be fine and the brakes will stop fast and hard like they should.

Robyn, mine is like you describe. Oh no, do i have a Robyn Issue?

If it's anything like what I described, I questioned this sensation when I had my Boxster. And that is what ABS feels like in our cars. It is perfectly normal. Every Porsche I have ever driven (So many loaner Boxsters...ug!) has felt this way and it's just a characteristic of the ABS of these cars. (As I have been told by two different mechanics...)

Isn't fade when you can push the pedal to the floor and nothing is happening?

Brake shudder is typically caused by excessive pad material embedded onto the rotor. This usually happens when the brakes are applied on hot rotors, such as in the pits after a run session, a small amount of material gets left on the rotor and you get shudder. I had this occur on the C2 I drove at PDE, by the end of the day it was fine.
The infamous warped rotors would also behave this way, although there is some debate as to wether this is a true phenomenon.

Normal Abs feel bracking over small bumps on the road.

Exactly!! So hard to describe yet you did it perfectly in so few words! :D Thanks!!

Correct. SANDOVAL is using the wrong term to describe what he is feeling.

In the case of fade, more and more pedal travel is required to stop, and the pedal becomes soft and spongy feeling.

The feeling SANDOVAL describes, is during braking on uneven or rough roads, the brakes on one or both of the front wheels feel like they stop working for a split second or two, BUT the pedal travel and firmness remains the same, and braking resumes as normal a second later. It may be that ABS is kicking in so fast and for such a short time, that there are no "pulses" in the pedal to communicate to the driver that ABS is active.

I experience this too in my 2003 911. It was a bit unsettling at first, but I am sure it is just part of the ABS system on these cars.