Some issues from a 2-day HPDE...
 

So I wanted to get some opinions about some problems I started having at the end of my 2 day HPDE at Sebring.

1. My coolant level was at Max at the start of the event, by the end of the 2nd day, it was slightly above Min. I never saw water temps get too high, slightly over half way. Is this normal? I don't think I have a leak or anything, no stains in my garage.

2. Towards the end of the 2nd day, I started getting a really bad shimmy whenever I braked. It happened no matter how much braking I did, and was mostly felt in the steering wheel. It was doing it on the way home too. Acceleration was fine. I swapped back out to my street pads (and wheels) once I got home, and the problem isn't there, everything feels fine. I didn't notice anything odd about the pads, they have about half life left.

3. I noticed on the way home that not only were the brakes squealing a lot when going slow, but even at speed if I broke even slightly. I know squealing at low speeds is normal for Carbotech's, but what about at high speeds? When slowing it sounded really bad, like it was metal on metal (as if the pads were completely worn I guess is what I was thinking. I did notice that the Ceramic brake lubricant had completely turned to dust when I removed the brake pads. Would that be the reason why? Any harm in driving under these conditions?

Thanks guys. I'll post my other thoughts (and videos) later.

My wheel shakes violently with carbotech and ferodo pads and my brembo calipers. thats one of the reason I am switching to stoptechs, that and the brembos not clearing my 18s with sufficient space between them. I think it has to do with pad deposits and the non floating rotors.

the brakes do squeal a lot after cooling from several heat cycles also, but normally quiet up again once they have fully cooled.

It sounds like you got deposits on your race pads. Did you cool them down properly? More importantly, did you bed them properly?

Hmm, would that be the cause of both of my braking issues? I didn't have the problems when I started the weekend, just finishing it up. I didn't bed them on my way to the track (no place to do it safely), but I tried my best to bed them while I was on the track when things started.

What is the proper way to cool them down? The sessions always end with a single cool down lap.

Your brake lube being 'cooked' will also cause a brake squeal. I would try to find another high-temp grease to quiet the shims down.

I'm using the Permatex Ceramic Extreme brake lubricant, is there something that can withstand temperatures better?

I run CarboTech pads and they have performed flawlessly at the track.

You just can't forget to bed your pads (CarboTech or otherwise). Why do you think CarboTech puts so many warnings on and in its boxes? And how is it even possible to bed your pads while on the track for a HPDE?

Just chock it off as a rookie mistake.

Also, CarboTech is very specific that you cannot use them on a rotor that has any foriegn pad transfer material on it. That means you must use new rotors, have them machined, or really go at them with garnet (not aluminumn oxide) sandpaper until all pad transfer material is gone.

CarboTech's get louder as they get dirty. And mine squeal like pigs at any speed on the road home from the track.

Keep in mind that your current rotors will continue to be a problem on the track. Your rotors have a high spot on them that needs to be removed. And don't waste your time trying to find garnet sand paper in any store. You can only find it on the internet.

And I had the same issue with lost coolant at my last 2 day event.

i completely disagree. as a carbotech xp10 user for 4 or 5 years, i have never had to replace rotors due to wrappage or deposit. you need to bed the pads in properly by doing 120mph to zerp stop. you have to do it to a point that your brakes are completely faded and it smells like you have to call 911. you only have to do that once, the pads should be fine to use after. i assume you have the big brakes right? wtf are you using lubes, not needed

according to a former pro, you have to do that only once. if you dont do it properly, the pads will never be effective again

The coolant level you're reading is not the true coolant level in the system. You're looking at the overflow/surge tank. If coolant heats and expands, it overflows into that tank. Conversely, vacuum as the system cools can pull coolant back into the cooling system from the surge tank if the main system's levels drop.

What I do is this:
When the engine is COLD, open the radiator cap (push down and turn) and fill the coolant to the very brim. Replace the cap. Then top up the surge tank to MAX with fresh coolant. Run the engine for 5-10 minutes and then remove the radiator cap a second time (only if the engine is cool). Top up again as needed. Now your coolant system is full and you have plenty of coolant in the surge tank.

Hmm, so the pads only ever need to be bedded once? Even if I switch back and forth from them and street pads? I did bed them the first time I went out, just not this time.

I thought using the lube was necessary? I know others were doing this as well.

So what would cause my wheel to start shaking a bunch after it was acting fine for the first 7-8 sessions? They were still braking great, I was just getting a ton of shaking in the wheel which got me concerned.

Also what would make them get so much louder after a few days of use? I mean, braking was ridiculously loud, it sounded really hard like it was metal on metal.

So if that is the case, wouldn't you want to refill the overflow tank when the engine is hot then? It sounds like if you filled it to the top when the engine is cool, then it would overflow above max? I checked the actual radiator level, and it was just about at the top there, just the overflow tank is low.

no lubes needed, they are for anti squeeling and for sliding piston calipers.

yes you only need to bed them the first tie you put them on to bond the new pad in (this is from a former indycar driver). thats why race teams usually bed a batch of pads in during test sessions.

you sure you didnt have a rock stuck between the pad and rotor?

vibration comes from deposits on your pad or rotor

The level in the tank doesn't change very much when the engine comes up to operating temp. So personally I'd rather have it at MAX with a cold engine, than have it at MIN with a hot engine. There is a lot of extra room in the tank above the MAX point, so it won't overflow.

You may have had some air in your radiator that was finally bubbled out with your high-rpm track day. Then when things cooled, the radiator pulled coolant from the surge tank back into the system and the level dropped. Or you're burning/leaking coolant, but you'd have signs (smoke/puddle).

Okay thanks. I'm pretty sure there wasn't anything stuck between the two, as nothing came out when I removed the pads.

So what can I do about deposits?

Okay gotcha. I'll just go ahead and buy some more coolant then. Any other places besides directly from Nissan to buy the coolant from?