mitch236

Alright, here is the story. Three GT-3's at the track last weekend, one of them an RS and all running steel. It was very HOT!! We were at Moroso and all of us experienced the same weird phenomenon. Everything is going fine for quite some time then I went for the brakes and got about 50% braking. No ABS and no lock-up. Pedal felt fine. This same thing happened to both other cars. It only happened once during the day to each of us and at the next brake zone, brakes were fine. Now I haven't taken temps yet or looked at the pad surface (I will tonight or tomorrow). The only thing we could come up with was overheating the pad causing out-gassing and preventing the pad from contacting the rotor.

The other strange thing is that all three of us are using different pads and one guy has different rotors. I was running RS-14's with Castrol SRF. The RS was on stock everything. The third one has Performance Friction rotors and pads.


Has anyone else experienced this? We are thinking about running Cup Car pads to see if that works.

cladd

Break in???

nkhalidi

With all due respect, this doesn't sound like it's that big of a deal. I'd chalk it up to an anomaly, or maybe a break-in issue. Did you try releasing the pedal and hitting it again, like a mini-brake-check?

mooty

was the breaking zone after a looooooong straight?
if you moved immediately from throttle to brk, after a long straight, the vac may not have built up? i know many elise/exige have this prob. and i get it occasionally on my 996gt3 too.

if your pads/rotors aren't brand new, and obviously you have tracked your car a bunch, i dont think that's glazed rotors. and SRF certainly shouldn't boil.

Erik

Mitch, I actually had it happen multiple times, especially going into turn 2 (slowing down from about 150 to 50) and turn 7/8, slowing down from 120+ to 25 mph. I actually had to let the Viper by because he would catch me under braking, and that was with a 3400 lbs tank, and the driver weights probably another 75 lbs more then me. I blame it on the stock pads, but it is interesting that it was happening with your pads too. Either way, I will stop being so lazy and install the RS19's for Sebring in 2 weeks, and we'll see what happens.

mitch236

I don't know if I would say it was not a big deal, it is quite disturbing when trying to brake and wondering if you will be going off track or not!

I did try release and re-apply to no avail. The brakes were properly seated.

Carrera GT

Three "same" cars exhibiting the same brake fade at the same time with three drivers -- that's an interesting case and not to be dismissed.

I guess you can start the elimination by saying it's probably not the pads or rotors (since that's the one thing really different about the three cars.)

I believe the brakes have a "pre-brake" feature to push the pads up against the rotor to prevent loss of assistance Moot is suggesting.

Slotted or drilled, unless they were choked with pad dust, the potential for getting gas trapped between the pad and the rotor is negligible.

What was the air temp?

Did no one measure rotor temps while this was going on? Did anyone do any diagnostics on the day?

Please elborate on the symptoms. You say "same pedal" and "50% braking" but I'd say that means you were having to apply more and more pedal pressure to get the braking effort required, meaning the pedal would feel different (because of the extra pressure.) I can guess the interpretation, but I'd rather you (and the other drivers) give first-hand accounts (not even trying to analyze it, just say what was going on.)

mitch236

Nobody did any diagnostics because we weren't expecting anything like this and didn't have any equipment at the track. When I say same pedal, I mean it wasn't soft or longer travel. Yes, I did push harder but the pedal was consistantly firm. The other thought we had is that maybe we overheating the ABS unit. BTW, air temps in the mid 90's

It's all very weird...

Next weekend we will do some temps

Carrera GT

Was everyone at the same turn and the same session?

If it only happened once was it only once bad enough to really think about it or were there other occasions but to a lesser extent?

It sounds like Erik (above) had multiple scares.

mitch236

Different turns and I only had it once. It caused me to have a "moment" with a tank slapper but all ended well.

It does seem that Erik had the worst of it. Hey Erik, did your buddy have any brake issues?

ltc

Not a big deal?
Trust me, anytime you go for the brake pedal and it's not there, it's a big deal.
Ask my driving suit and my dry cleaner....I'm sure they've got stories to tell.

nkhalidi

Is that the same as "pre-filled brakes" that poster #10 was discussing here?

https://rennlist.com/forums/showthre...7&page=1&pp=15

I've never heard of "pre-filled brakes" before. And apparently C4/Targa4/Turbo have them, while C2 doesn't? I guess the narrow-body GT3 falls into the latter category?

nkhalidi

My point was that if it only happened once in the entire day, there's a chance it might be an anomaly. Heck, I've had my fair share of braking "moments" - everyone has.

I guess I never got really worked up about it; was kind of like, "well, maybe I overheated the pads, I'll let them cool down for a couple turns then get back up to speed." Maybe I'm too relaxed.

GrantG

I think this is an intentional weakness built into the steel brake systems (in the ABS logic), so more customers will be forced to pay the big bucks for the PCCB's

Nordschleife

I think you need to revisit what actions each driver took. Frankly, for most drivers, if they put, say 50 lb of pressure on the brake and get less reaction than they expected, they then redouble their effort and put 100lb on the pedal. It would be unusual to put 50lb of pressure on the pedal, have the system react the same as when you put 25lb on the pedal and not do anything aboiut this.

Next I would wonder what happens if I leave cars out in the sun when it is really hot, after track use. Possibly, under these conditions, you should bleed before each track session. Try it again on a really hot day, and then have somebody who knows hydraulics check out the system, you may find you have introduced airlocks in some way, for example.

On really hot days, rubber lines can expand more than expected.

R+C