More brake trouble - at the end of my rope!

[steve_wilwerding]

have been dealing with brake issues all summer. In June, I noticed that the brakes were getting spongy. On a track day in July, the brake pedal kept getting lower and lower, the brakes were not effectively stopping the car.

So, I started changing things. Got brand new OEM rotors. Flushed the brake system three or four times. Swapped different kinds of pads in and out. Finally, it seemed that the brakes were squishy all the time, so I took it into a dealership where they replaced the master cylinder.

That seemed to help quite a bit. The brakes are no longer squishy. However, I have found that pedal travel starts to vary. For example, when I first start out from the garage, the brakes are rock hard, and the pedal travel is minimal before the brakes start to work. However, if I drive for awhile, the brake pedal has a lot more travel before the brakes engage. I started thinking that this might be caused by runout on the rotors, but these are brand new rotors, and they seem to exhibit the same tendency on my old rotors.

So, this weekend I start thinking that my wheel bearing might be going bad, and sure enough, driving last night with the top down, I started hearing a high-pitched whine/squeel when going slowly around corners.

Does this seem like a reasonable conclusion? Unfortunately, my dealership mechanics are idiots, and I've already had it there once to fix this issue, which obviously they didn't. Any other ideas about what this might be?

I'm getting really ticked off that this has been a problem for so long, and that I keep missing track days because my car isn't in shape.

[ar38070]

I would not think the wheel bearing has anything to do with it. If the bearing were bad enough to cause brake problems you would have noticed other problems first.

Also usually when the bearing goes bad the noise is more of a low pitched rrrrrrrr or moaning kind of noise. At least that what mine have all sounded like and I have replaced four of them.

I do not think that a brake pedal that changes height from the cold start position is anything to worry about. As long as the pedal is consistent once the car is moving then I do not think you have any problem.

It sounds like you have not had the car back on the track since the master cylinder change. If that is that case then (assuming your high pitch whine is not some other problem) then take the car to the track and try it out.

[986Jim]

If porsche changed the master cylinder then either they left air in it,or the fluid is not high enough rating anymore.

Something is changing from when the car is cold to hot if they work awesome cold and suck hot. Generally it's either air in the system or the brake fluid is not a high enough rating. If your using DOT 3 then switch to non silicone DOT 5 and give that a whirl, it has a much higher boiling temp and won't let the brakes go soft.

Also what pads are you running on the car? Try changing them out for something with a more temperature resistant compound.

It's not the bearings however, if anything when they get really worn they would help stop the car with all the friction but would not effect the feel of the pedal

[Topless]

Look real hard at your hydraulics.

Spungy, soft, fading pedal, all point to hydraulics. Is there any fluid leaking? Air still trapped in the lines? Bad wheel cyl? Bad (new) Master cyl? Wrong fluid? That's about all there is... did I miss anything?