Mike Murphy

I don't know if this will help you, but I had the same problem after doing a DE event. Before the event, my brakes were solid and I flushed the fluid with ATE Blue. Still solid. After and during the DE, I found that the brakes had quite a bit more travel than before. Even after cooling, the pedal wasn't as firm as before.

I talked to my mechanic and he said that it's probably not the fluid and most likely the pads. I'm still curious to find out what caused it.

0utlier

Just an update to put my thread to rest and maybe help someone who has this problem...

The issue was air in the lines. We ended up bleeding the brakes 4 times to get all the air out. We would bleed and then let it sit for a little while, then re-bleed. Multiple bleedings finally firmed up the brake pedal. Hope that helps someone.

GUMBALL

It is not unusual for the pedal to get soft after a track session - sometimes the brakes get hotter than you think. The solution....bleed the brakes. Usually, all it takes is a few pumps - just enough to get fresh fluid into each caliper......and, without a power bleeder, bleed a front and a rear at the same time.....

That is why it is standard procedure on a track car (race car) to bleed brakes after EVERY session.

Mike Murphy

You are absolutely right. I did some research and spoke to the mechanic. The question is, why the need? I assume it's because even though I'm running ATE Blue, the brakes still get hot enough to cause gases to escape (if not boil) to some degree. Is this the reason? BTW, I was running stock pads, so that can contribute to the increased heat.

GUMBALL

Heat will cause microscopic bubbles to form in the fluid, and that is all it takes.

Semi-competition (or full comp.) pads provide a higher friction coefficient. This permits the car to brake "harder", reducing the time on the brakes, which in turn, reduces the amount of heat generated..

Also, as an instructor, I have noticed that many drivers at track events do not use the brakes correctly or efficiently. The tendency is to brake early, not very hard, and stay on them too long.

A fast race driver will brake at the last inch, use the brakes VERY hard, and then quickly get off them. It may not seem that way, but this method does create less heat.

Mike Murphy

There you go. It was my first DE, so I'm sure I wasn't using the brake correctly.

a4sfed928

I disagree with this statement a braking system converts the energy of the moving vehicle (speed) into heat. If the same speed is removed from the vehicle then the same area under the temperature plot should be observed in the braking system.

Charley B

And that contradicts Gumballs statement because................................?

Mike Murphy

Help me understand something. My logic tells me that it takes the same amount of energy to slow a car from 100-0 mph regardless of how long it takes to do so. Just like it takes a certain amount of fuel to bring a car from 0-100mph. The difference is in "time" and can be measured in "horsepower."

So let's say you have a car with 200 horsepower vs 400 horsepower. The 400 horsepower will accelerate faster. The same can be said of brakes. Most brakes on a Porsche far exceed the engine, so to bring a car from 100-0 in 10 seconds might consume 500 horsepower vs 100-0 in 7 seconds might take 1000 horsepower.

So if stopping a car faster requires more horsepower, then how can that generate less heat on the braking system?

Charley B

It isn't the amount of energy produced to slow the car that creates the problem. It is the amount of heat transferred to the fluid. The longer the pads and rotor are in contact the more heat is transferred through the caliper to the fluid. Dragging your breaks for a few blocks will heat things up much more than one panic stop.

Mike Murphy

I guess the same can be said for the clutch?

LeonB

Scott
If you pump the petal all the way to the floor trying to bleed the system you can trap air in the system. That was happening to me. I purchased a power bleeder pumped it up to 5lbs and flushed the system. Breaks are working good now.

GUMBALL

Precisely. Thank-you.