warped rotors?

[ChrisZang]

I spent two great track days at Thunderhill last weekend

In the middle of day #2 the following started to happen:
When the brakes were hot and I was doing heavy breaking from high speeds (example breaking from ~ 115 mph for turn 1 or at turn 9 or turn 14) the car felt like I was braking on a "washboard" surface, meaning that the car became a bit unstable and started to "wobble"

This was NOT the ABS, which feels different, I also did not have brake fading and I had pretty much the same brake distance as before, so the brakes generally still worked great. And it only happened after a few laps when the brakes were hot.

My best guess is that I have warped rotor(s) in the front, so before I go out and buy new rotors, here are my questions:

a) does anyone have a better idea?
b) is there a way to test if I have warped rotors
c) why would that only happen when the brakes are hot?

P.S.: I see no cracks in the rotors
P.P.S: Nobody else seemed to have that problem, so I am sure it was not the surface of the track itself

[Adam]

You can usually feel warped rotors through the brake pedal and steering wheel when slowing down. Do you still feel something now or has it gone away? If it's gone now, then it's something else. Rotors don't warp then go true again. The brake system on your boxster S should be able to handle what you described just fine without warping.

[choeglund]

Check your lug torque to make sure everything is tight. If you still have pulsing in street driving then good chance you need to replace the rotors. Do the pads at same time.

[skip_168]

Pull the pads.. depending on what kind u have, u might have glazed the pads over...

[Sisu guy]

I want to re-open this thread. I just experienced exactly the same contions Chris reported! When cold the Braden's are fine, no judder. Once hot on the track they get progressively worse!
I'm confused as to why I do not feel anything cold? If they were warped I would assume I would see it all the time?
Thoughts?
P.S. 2000 S with std. Rotors

[BYprodriver]

Worn wheel bearings + old grease? Try SKF wheel bearings.
Excessive toe out alignment?


Thanks for searching before posting!

[husker boxster]

I wore the left frt pad out on my CSS at COTA back in May. I was going to change pads over the 4th of July (been driving my LE since COTA) and I figured I should have the frt rotors trued up before putting pads on. The guy at O'Reilly's calls me back and says 1 of my rotors is warped. Picked it up and sure enough, the left rotor was very warped. I had driven 3 day at COTA and warped it sometime during my track time and drove 1000 mi back to OMA and never felt any shudder while braking. I was surprised but it defn needed replacing. So you could have warped rotors and not know it.

Bought a nice set of Bosch zinc rotors for $80 ea at O'Reilly's.

[crooster]

Sometimes uneven brake pad material transfer to the rotor is the cause of pedal pulsations. You can usually sand this off.

[Topless]

Originally Posted by crooster

Sometimes uneven brake pad material transfer to the rotor is the cause of pedal pulsations. You can usually sand this off.

Warped rotors are possible but uneven pad transfer is the cause 99% of the time with our cars. You can measure runout to check for true and if still good a thorough rotor cleaning and re-bed of the pads will probably work. Remember that front rotors are not too expensive so don't spend weeks trying to save them. Sometimes new is the simplest solution.