93Rubie

I auto-x my C4 a good bit. This spring I did a complete flush of the system using fresh DOT 3. I did a drivers school last Sunday, we split 8 cars into 3 heats. I was in heat 3 so only 2 cars. We where doing back to back runs on a fairly open and fast course. I bet I was seeing 60+ easy. Hard to tell, I was NOT focused on my speedometer.

At any rate, on the 8th run, the pedal very suddenly went to the floor.
Previous to this I had noticed a little brake pad "hot" smell. Brakes on the 7th run still grabbed great. We (me/instructor) go got the car stopped by coasting in gear. The red brake light was on/ABS active was on for a bit, then went out.

Fluid level ok, no external leaks, after maybe 1 or 2 minutes of checking things out, we hit the pedal and it came right back. We let it sit over lunch. I ran it all afternoon with no issues, however, after about the 5/6th run, we let the cars cool for a few minutes.

Initially, I thought I may have had a master cylinder issue. However, the brakes worked and the pedal did not sink. The fluid was clean but after the "event" it was cloudy and nasty looking not black just a darker amber.

I ran this by a another guy who really knows C4's. He seems to think I boiled the fluid. I tend to agree. Keep in mind my C4 has the base 12" 2 piston front calipers. Not the 13" J55's. He said, this is a problem with the base 12" system.

I'm going to completely drain the system and fill with some Motul RBF600.

I never had an issue at a normal auto-x, just this drivers school.

Your thoughts?

SouthernSon

Left foot braking?

93Rubie

I never left foot brake, ever, so I doubt it.

Sidney004

What type of pads?

Kubs

What type of pads are you using? DOT 3 is not very high temp fluid. I use AMSOIL brake fluid which works just as good if not better than the Motul but it costs less.

AMSOIL DOT4 Racing Brake Fluid
http://kahunamotorsports.com/bf4-product-page.html

93Rubie

The pads are whatever came on the car when I bought it. So IDK? They work ok, bite good.

This was NOT brake fade, where you need more pressure to get the same stopping force. This was good brakes, NO brakes, like flipping a light switch.

Kubs

A cheap pad not designed for heat will transfer that heat into the fluid faster than a proper track pad.

Those 12" brakes are way too small for heavy braking. I even hated the J55s when they were on my car.

Painrace

SRF!

Jim

Rob31

Ate super blue or gold is better than what you have .
I could set a stock brake pad 12 " on fire in two laps if I wanted to at Blackhawk .
Get some decent pads /fluid . Dot 3 aint gonna cut it
I now have the 13 " rotors .

c4cruiser

Even within the DOT3 fluids, there is a variety of wet boiling points. What fluid brand did you use? A decent DOT3 fluid is the Ford Motorsports HD fluid (yes, FORD ) with a 290 degree wet boiling point. Slightly better is the Castrol LMA fluid at 311 degree wet boiling point. With stock tires and stock brakes, either of these fluids should work fine for autocross where you see 60 MPH speeds.

I have used the Castro LMA fluid and it worked fine on my old 92 that I occasionally used for autocross and a couple of track days. The pads were Hawk HPS and I never saw an issue with boiling brake fluid.

Is there any indication of brake fluid leakage around the ABS unit in the copmpartment behind the driver's seat? With the two warning lights that came on in the DIC, it's possible that the fluid level was not as high as it should be. If the fluid is even a 1/4" below the top of the fill hole, very hard braking can cause those lights to come on.

I use ATE Super Blue in my '87 autocross car and haven't had any issues with boiling fluid. I have a C5 front brake conversion and no brake cooling ducts. I do a few track days each year and never boiled the fluid. The front pads are stock C5 Z06 and the rear pads are Hawk HP+ for stock-size 87 rear rotors.

Canam

Has very little to do with the caliper size. Its all about the ambient temperature of the day, the type of brake pad your using and the fluid your using. Also, your never, never going to be assured you won't boil the fluid. I boiled SRF at Shannonville at the end of 10 laps into a 12 lap race which I was leading. It was over 40 degrees celcius, high humidity, and the track requires a lot of braking. I had porterfield R4 pads on and brake ducts.

From your situation you used a brake fluid with too low a dry boiling point and too crappy pads that were transferring too much heatto the rotors. I don't know about the weather or your driving style.

Just grab some good dot 4 like ford racing or castrol srf ( very expensive) and get yourself some hawk blues because they make them for your caliper (which has limited performance brake pad choices) and try again. You will be reasonable very happy. I use ATE super blue now. Its pretty good stuff and cheap.

93Rubie

We looked at the ABS unit at the event. No leaks.

I've heard Motul RBF600 is good stuff to.
I think some better pads are in order too.
I need to check out my rotors and see if they are fit for replacement or ok to use.

I'm going to start with a complete brake system flush and go from there.
Thanks for the help.

froggy47

IMO you experienced a combination of incorrect pads and (maybe) fluid. Put some better pads (I like hawk hp+) and fluid (I like Wilwood 570) and let us know how that goes.

Don't sweat it, this is fixable.

I don't think you "boiled the fluid" I think you had the wrong pads for the job.


The base 12" system is fine for autox, my C4 96 LT4 had j55 and I could drive it over the capabilities of some "street" pads. It doesn't take much to go over the capabilities of street/stock pads.

I doubt you need srf, ate, or motul although they are ALL great fluids.

Ck my sig for what i have done with the Ford fluid & more recently with Wilwood 570 ( a GREAT VALUE high temp fluid).

C66 Racing

For a street Vette the fluid Kubs listed above is fine (and what I use in my daily drivers). For the track I use AMSOIL's DOT 4 in both my brakes and clutch:
AMSOIL Series 600 DOT 4 Racing Brake Fluid (Product Code BF4SN)
Dry Boiling Point - 580F, Wet Boiling Point - 410F

rayk

If it's ceramic pad, you could overheat them. Like others said, change the fluid and pads. Mostly likely problem solved.

rfn026

Right now we have no idea of how hot your brakes actually got. I run about 1200-degrees at the rotor in my C4 and have never had a braking issue. My calipers run maybe 400-degrees.

Richard Newton

jaa1992

Had both problems when I had an 88, 12" brakes would fade and/or boil the fluid - even the motul!

If you are going to continue using the car for track events here are my suggestions:
Brake ducts - number one!
Good high boiling point brake fluid (ATE, Motul, etc.)
Carbotech xp10 front, xp8 rear
Good braided brake hoses

Rebuild the calipers - maybe

Have fun and be safe out there!

Kubs

93Rubie

Good Idea,
I think I'll take my IR gun next time. I'll know for sure, what my temps are.

After next weekend, the new stuff is going on/in. Thanks for help.

Next auto-x is Aug. 5 tentatively. So we will see.

TJM