rickkym

I've been auto-xing for a couple years, ran an event mid-may and all was fine. The next week at an event on my first run i get brake fade mid-course (sixty second long course) and by the finish the brake pedal is going to the floor. The car seems fine on the street and pumping the brakes brings the pedal back most of the way. Hitting the brakes hard going down a steep hill the abs seems to act fine.

I ran a full quart of fluid (prestone dot3 synthetic) and bled the system, still pedal fade. Took the pads off one side and the front-rear taper is maybe 1/32nd if that.

There is no fluid leak and there are no codes being thrown and no idiot lights come on. All i can figure is 1)bleed the ABS but i have no tech tool 2)bad master cylinder seals 3)maybe the brake booster or a vaccuum leak there? I do turn off the traction control mid-course on occasion due to being forgetful at the starting line.

please help with any thoughts/ideas. Thanks in advance!!

froggy47

How many miles on the m/c and slave?

burners

Have you checked your wheel bearings? Also, is there any evidence of leaks for any of the calipers? Shouldn't you be running at least DOT4 brake fluid?

c4cruiser

With no leaks visible and fresh fluid (for slower-speed autocross courses with speeds below 50 or so a good DOT3 is fine) I would be thinking a bad master cylinder that could be leaking internally.

You might check on the interior side of the firewall where the M/C rod goes thru to see if there is any moisture in the boot or any signs of seepage.

If the booster was bad or a vacuum problem, I would expect a hard pedal.

rickkym

The car has 51K on it, i bought it at 42k and have been autocrossing and done a few track days but thats it. I really don't drive it unless to an event (~1 hour).

None of the calipers show leakage, there is no leakage around the master in the engine compartment either. I'll have to crawl up and look where the pedal goes through the floor (thanks for that tip!)

The weird thing to me is that is seems to have developed this condition in a week sitting in my garage between events. The fluid was all brand new early last season.

Thank you all for your help with this, i really appreciate it!!

gonzalezfj

Brake fade is when you have a hard pedal but little braking action. This is caused by overheated brake pads.

What you describe is a "long pedal". There are many possible causes. Most common is a bad wheel bearing that allows one of the rotors to wobble and knock back the caliper piston(s). Then, when you go to apply the brakes, the piston has to travel a long distance before it contacts the rotor, thus the master cylinder has to travel a long distance also and the pedal goes down, sometimes all the way to the floor. Jack the car up at each corner, then grab the wheel at 12 and 6 o'clock and try to rock it. If it has any wobble at all, replace the hub. Also, if you have removed the rotors, you may have trapped some dirt or other crap between the rotor and the wheel hub, causing the rotor to wobble. This is a no-no.

You could also have a bad master cylinder. No solution other than replacing it. With the car standing still and engine running, apply steady pressure to the brake pedal for several minutes. Note if the pedal sinks with time. If so = bad master cylinder. A bad check valve happens instantaneously; good right now, bad the next time you try to use the brakes.

Third, you could be boiling the brake fluid, but this never happens in an autocross because of the short duration of the run, plus you are stopping from relatively slow speeds (60-70 MPH max.). DOT 3 is all you need.

If you have air in the system, the pedal will ALWAYS feel spongy on initial application (i.e.: without pumping the pedal). From your description this is not the case. If you get a hard pedal with the car standing still (see above) you don't have air in the system.

Your booster is fine. A bad booster gives you a hard pedal with little braking action, not a long pedal.

Finally, make sure the caliper pins are clean and well lubed. A sticky pin could cause the symptoms you describe.

Hope this helps. Please let us know what you find.

Frank Gonzalez

mgarfias

Never?

avizandum

I cooked my DOT 4 brake fluid doing multiple hot laps on a wide-open airport course last summer - quite possible.

rickkym

so i did a complete inspection... all i found was one loose bolt on the RF wheel spindle/bearing hanger but there was _no_ play in the wheel. I'll give you a guess as to which of the three bolts it was.... if you guessed the one just in front of the ball joint stud making it a royal pain-inthe-a$$ to tighten Don Pardo will tell you what you won.

So i have a bad master cylinder probably leaking internally. Do you know what a 'rebuild' kit costs? $75.00 for TWO O-RINGS???? do they have to form these in space during a shuttle flight, or are they pressed between the thighs of a nubile aztec princess????? I can get two o-rings from the hardware store that look like a perfect match for three-freaking-dollars!

Thank you BIG TIME to all those who helped...

meldog21

You can buy a brand new master cylinder for about $200.

Dog

froggy47

Zenak

good pads & 600 motul fluid

Brake fade suddenly is usually either:
Pads heat glazed or fluid boil over