froggy47

Happened at an autox which did have a very heavy brake from maybe 85 to almost stop, 11 laps .

Rotor spec was near min. but I don't think below. I'll mic it later. White box.

So question is, what is the physics of how this happens? Too many heat/cool cycles & some void or impurity in the metal just lets go?

This is fully thru the outer "plate". Pad was fine, I think it happened on the "cool down lap" driving home from event. Ambient maybe 60f socal.

Thanks.

I only use 1 jack stand in the back and 1 in the front, are you supposed to use more?

JK

sleeper02Z06

Contrary to what many will say, most rotor cracks are due to improper cool down. It is the single biggest reason, I'd say on the order above 90%, that these big snap cracks happen. I'd be willing to bet it happened while the car was parked after the run, you simply didn't notice it until the drive home.


Joe

froggy47

You may/could be right. At autox there is no place/way to do cool down, unfortunately.

Thanks.

At least they are only 35 - 40 bucks a corner.



Probably why the rubber boots melt off the calipers, too.

Last C5

Ah yes, setting there in the pits with your nice cold bottle of water after a very fast, very warm 20 minutes of open track when you hear that telltale "tink" sound and you know you're about to spend the next 15 minutes changing a rotor.

Take your cool down lap and get the temps down as far as you can. Then right after you get parked in the pits get out of the car, get your helmet and gloves off, and move the car about a foot forward or back.
Move the car about a foot every 3 or 4 minutes for a couple more times and sometimes this helps keep the rotors from cracking. The problem with just letting the car sit is that one section of the rotor is inside the caliper and cools far less than the part of the rotor outside the caliper and TINK.

The Spark

I bought some cheap NAPA rotors and got maybe 2 weekends before the fronts cracked. Before first session - second day, I drove my car to get some gas and then back to trailer without any problems. Then drove to grid and didn't notice any problems. Pulling out of grid I got on the brakes a little to warm them up and noticed a shutter. It wasn't real bad but definitely could feel it.

I had to drive the entire 3.1 miles to get back to the pits. I thought I had a low/flat tire after driving to the pumps. Asked a worker to check my car and he said it all looked find so I went back out. Still felt the shutter when applying brakes.

Long story short - big crack in left front rotor and lots of little cracks in both fronts. Cool down lap the night before was about 2 miles long but I can see where proper cooldown might have saved them. I might have gotten the entire weekend out of them.

Will take Last C5's suggestion and move the car a little after parking in pits.

MungoZ06

Sometimes they just heat check ...
Before I went out on a session at WGI last year my rotors looked like this:
Spider lines

When I came back in from an easy session in the wet I ended up with this
Cracked rotor



And yes ... I do the cool down lap and roll the car in the pits ...

shifter77

REPLACE

billla

To put it mildly, yes. If that jack slips or bleeds down and your legs are under the car, you'll suddenly be too short to use the walk-up window at McDonalds. The arrangement you're using looks unstable in the extreme to me.

Never get under a car that's not fully supported. Plenty of articles here about how to jack a C5.

throwit

Welcome to the club...

I have cracked a rotor every time I have ever been to the track...sometimes 2 or 3 in a wknd. My cool down lap is without brakes and I move the car also, seems to help to a certain degree, but they still break (even the rears!!). I think it is just a trait of the stock calipers.
Almost every vette driver I have met on track who is NOT breaking rotors, is either not using aggressive pads and/or not braking nearly as deep as they could be...

2K3Z06

I do about 3 or 4 track days a year, and have never cracked a rotor. But, since my car is street legal. I will pull off the track and head down the road for about 3 or 4 miles. Once I see my oil and water temps drop down to about 200 or 220, most of the heat has been disapated. And the rotors are a lot cooler also.

As posted earlier, cracked rotors are from parking a car with very hot brakes. Do an extra cool down lap or if your street legal, cruise down the highway at 55MPH for a couple of miles and your equipment will last longer.

Using a laser thermometer, my rotors are around 400 degrees coming off the track, after cruising down the highway when leaving the track, my rotors are under 200 degress.

Try it. It works.

VetteDrmr

I don't understand this comment. I just roll down the road leading to the course site, keeping my foot off the brakes as much as possible. Takes about 5-10 minutes total, then I park it. I've never cracked a rotor in autocross since I started in '00.

HTH, and have a good one,
Mike

froggy47

At Cal Spdwy for example, we are "strictly" confined to our lot til the end of the day. Insurance regs & security patrols, etc. No cruising around the speedway. Cool down laps thru the pits are frowned upon by fellow competitors.

froggy47

ROFL.

Gee, thanks for that.

sleeper02Z06

Sorry, couldn't resist buddy! That 90% i venture a guess about, well the other 10% involve scenerios like this. Rotors that should have been replaced due to heat checks, rotors that are new and not properly heat cycled before heavy use, etc etc. Anything can happen, we all know that, but i really do stand by the cool down percentage.

Joe

froggy47

Wow tough audience, next time I will right JOKE at beginning and JOKE OVER at end.

BTW there are 4 points lifted in the pic, funny what a camera angle will show. Jack stands go under when I go under.

sleeper02Z06

Ugh. I don't know how to put this kindly but if you snap rotors EVERY time you have been on a track YOU are doing something wrong. Pile driving the brakes senselessly, not cooling them down, not seasoning the rotors before use, something. Whatever it is you are the issue. The calipers have zero to do with snapping rotors.

FWIW In all the years I have been tracking cars, Camaros and Corvettes, to include 3 years of National SCCA Racing, I have only ever snapped ONE, yes ONE, rotor. That was after a qualifacation hot lap bailout to avoid a black flag for sound at NHIS in 2007. I whipped off track from a hot lap and was impounded immediately. I heard it snap getting out of the car. Thats it. Been on Wilwood pads, Hawks, Carbos and EBC's. I hear this crap all the time about if you are not snapping rotors you are not driving or braking hard enough. Heat checks yes, clean breaks no. I didn't win a Divisional title at the national level by braking like a pushover. Ask anyone on here how I brake, better yet, run with me on track. Your question will be answered.

Joe

burners

+1 on that. 4 jack stands is the safe way to do it. Don't trust hydraulics.

MungoZ06

Yeah, Joe ... I know ... I looked at them end of the previous day and said ... should I replace them now? (knowing that we had rain coming in and a slower day coming)
First cracked rotor I've had ... this set was the worst chinese metal I've experienced ...

VetteDrmr

I've never cracked a rotor. Nine years autocrossing and DEs resulted in rotors filled with heat checks and rotors worn down too thin, but never cracked. I've always been able to take a cooldown lap or cruise out of the autocross lot (my car is street-legal), and I'm not that slow!

My feeling is that you've got to be putting some massive amount of heat into the rotors. Left foot braking? AH always on? Something's not right.

Froggy, can you not go out onto a public street to go get gas, food, etc? I admit I don't run with SCCA, but that sounds awfully restrictive to me.

HTH, and have a good one,
Mike

froggy47

I DO LFB & have measured temps of 450f after a run. No to AH, all off. As to lunch break yes, but I would need to exit the grid each lap. Sometimes a line will not get run for 10 minutes (between runs). So for practical matter there is NO driving around after a run. Just park it back in the same line & wait for next run.

I will try leaving space & moving the car a few inches & see if it helps. Between runs we are always busy setting tire press & watering tires etc. It's quite different than a track session.

Also after last run maybe drive around a little "lost" trying to get back to pits.



Also this event where it happened was especially high speed down to almost stop due to course design & so temps may have even exceeded 500f & then park it & full cool off with no car movement.



Thanks.