skxf430

I was tracking my Z06 today and my car seems to have developed a stiff brake pedal at times. Particularly, when coming down the front straight at about 145 MPH and slowing down to about 90 thru the first corner, I am on the brakes real hard.

But it seems like my power assist (booster) isn't working on my brake pedal. The pedal is rock hard and the car doesn't want to slow down. The brake system is properly bled and the brakes aren't fading, but maybe I have a bad brake booster?

It gets a bit unnerving not knowing if I will have any brakes.

Anyone else have this problem?

Thanks for any info

BEZ06

Like I said in the thread you started in the Z06 section, if you're not running a high temp race compound pad I suspect fade due to glazed pads.

If you have a firm pedal then your fluid is up to the job.

However, a firm pedal with no effective braking sounds like a pad problem to me!

Bob

naschmitz

Could be "Ice Mode." Pedal goes hard, no ABS pulsations, brake bias all to the rear. Releasing the brake doesn't shut it off -- it is programmed to expect the driver to pump the brakes. It is really frustrating on an 80-F day!

To prevent it, you have to apply the brakes in a manner where you will not get multiple wheel lock up. The example below is triggered by a pavement transition and three wheels locking up simultaneously. I've also had it where the braking zone crests and you apply the brake at the crest when the car is light. No chance of staying on the track in either case -- you will be driving off if it is Ice Mode.

http://forums.corvetteforum.com/auto...m-solo-dl.html

naschmitz

If you are not running high temp pads, Bob's answer is more likely the cause.

BEZ06

Bert's mention of ice mode (or what that poster in your other thread called ABS freeze) is a definite possibility.

Especially if you've got some aggressive track pads and are running a street tire.

Tires are what stops the car, and if you've got more brake than the stickiness of your tires can handle, then you'll be into the ABS in the hard braking from 145 mph that you describe.

Even if you're on an R-compound tire, if they've got a lot of heat cycles on them they will become greasy and you could easily be into the ABS in your hard braking situation.

I know your not looking at the DIC when braking hard for a corner, but if you experience it again try noticing if you're getting a message that ABS is active when this is occurring.

Bob

redtopz

I'm guessing you were at WSIR since you're from LA. That's a bumpy brake zone so you probably triggered ice mode there. I experienced the same thing in my T1 car during my first race weekend at that track. Solution is to brake slightly earlier and lighter on the pedal so you don't lock up the wheels.

Screamin Z

Check the vacuum line going from the back of the intake into your brake booster. Had this come off and the car wouldn't idle properly. Plus pedal was rock hard.

skxf430

My pads are Endless ME20's and they are a high temp pad, and they are not glazed as the brakes are function fine everywhere else on the track. I am using Toyo R888's with only about 15 heat cycles on the tires and they are in good shape, and the ambient temperature was only about 60 degrees.

I could be experiencing Ice Mode or ABS freeze as the pedal is dead stiff. Could be of the way I am braking now as I have gotten more comfortable with the car and have gained a lot more cornering entry speed.

It certainly didn't give me too much confidence, and I left WSIR yesterday just after a few sessions. I will definitely try to brake earlier and with a lighter touch next time. What made things worse yesterday, was their weren't any reference cones laid out for the braking markers into 1 so it made things a little more challenging.

skxf430

Here is an interesting read over on the Rennlist board talking about the same braking symptoms.

http://forums.rennlist.com/rennforum...ly-got-me.html

froggy47

I have experience with ice mode, however on a 2004 z06 the recovery is different from previously posted. Multi wheel lock up ( I don't think it needs to be all 4) puts you in ice mode, you are allowed approx 20% braking power.

To get out fully release brake, all 4 wheels spin up to speed (wheel speed sensors) and (on my car anyway) brakes are back 100%, No need to pump the brakes.

Now if you are sliding on grass this could happen several times hence the impression that pumping the brakes is required, but if you are on pavement a quick full release is all that's needed.

As suggested if you know there is a rough braking spot on the track an adjustment to the nut behind the wheel is in order.

geerookie

This more than likely has something to do with it. The other part I would check is the check valve on the end of the hose. It's the plastic piece that connects the hose to the booster. These can get plugged up from too much oil blow-by in the intake and cause them to stick intermittently resulting in no power assist.

http://auto.howstuffworks.com/auto-p...ower-brake.htm

skxf430

Randy Pobst mentions the ABS hard pedal here.


Go to about the 10:28 mark.