911mhawk

Posted this in the turbo side too but thought may get some feedback here from more track folks:

Wondering if others here have had the same experience where after a good hard 30 minutes of driving your ABS quits?
Typically we run 20 minute sessions with a 20-40 minute break between depending on amount of drivers/skill classes.
When I do just the lunch hour I'll run a little longer and usually it's a faster group and with no DE traffic so you can have several fast laps back to back.
A couple times last year, and again yesterday, I get the ABS warning light and don't have ABS. Drive a little w/o it for fun, realize it's nice to have when slowing from 150>75, then go park it for 10 minutes and back out with ABS working fine again. PSM is unplugged at the pump and car has 380/350 brakes on NT-01s that are at the sweet point (1/2 done).

vandersmith

Maybe cooked one of the speed sensors?

TheDeckMan

I would look at the sensors for damage, perhaps a wheel bearing moving around hitting one sends the ABS into a tizzy. Had a similar thing happen on my Audi TT's ABS and had to use the run off once. Bearing was getting worn and clipped the sensor with the ring slightly.

Gofishracing

try to pull a code. It will tell if sensor- YES wheel being can do it- Ask me how I know.

911mhawk

Thanks guys, I'm hoping it was just my fluid being at FULL mark rather than a little below, I think this caused it in the past a couple times and I resolved it by pulling a little out.
Have new bearings from last winter when I did GT3 uprights and new rear hubs & bearings too but will be pulling codes this evening to see.

vandersmith

Thought it might be a speed sensor - had this happen a few times.

Strangely, my C4S did not have the clip on dust covers that my GT3 has on the sensors. The sensors are magentic and will attract a ton of rotor debris. You might try to find those fabric covers/shield things while you're in there.

Use a good set of allen head sockets to get the speed sensors out. I broke one inside last time.

Good luck!

Gofishracing

yes. inspect sensor . I'm amazed no heat shield. sometimes stuff inside rotor hat can effect. clean out. compressor . Giro Disc. worst my feelings .

black04

Why would full fluid case a problem?

vandersmith

Sometimes when there is too much fluid in the reservoir, at the track the heat causes the fluid to expand and it can literally "pop" through the reservoir cap causing your brake pedal to feel mushy.

Its not a faulty cap. Its too much fluid expanding with nowhere else to go and with enough heat and pressure the path of least resistance is through the seal on the cap.

This drove me nuts for an entire hot summer track day until I realized simply draining some out of the reservoir until its just above the minimum point solved the problem

Gofishracing

Vandersmith- Those tires too old to use? Cup 1's. What year 2011, 2012 ? Ok for car storage.

black04

I understand the heat and fluid expansion, but the fluid overflowing the reservoir doesn't make the pedal mushy. It's the overheated pads and fluid that do that?