Disappearing Brakes !!!!
Discussion
I did my first trackday yesterday at Donnington in my 911 (1992 3.6 litre). Fantastic - the most fun I have had with my underwear on, by my car failed me !
After about 6 reasonably hard laps chasing a much later 911, I came under the Dunlop bridge at 120 mph to find that my brakes had virtually disappeared, and following my first brown trouser moment in quite a long time, I just managed to get around the chicane and dived into the pit lane.
Car is running cross drilled disks with standard pads on the front, with std brake fluid.
After about an hour of standing, brakes were as normal and I drove home with no probs.
Did I boil my brake fluid ? I had visions of having to remortage again - which is not easy these days - just to put the brakes right.
Any ideas ??
After about 6 reasonably hard laps chasing a much later 911, I came under the Dunlop bridge at 120 mph to find that my brakes had virtually disappeared, and following my first brown trouser moment in quite a long time, I just managed to get around the chicane and dived into the pit lane.
Car is running cross drilled disks with standard pads on the front, with std brake fluid.
After about an hour of standing, brakes were as normal and I drove home with no probs.
Did I boil my brake fluid ? I had visions of having to remortage again - which is not easy these days - just to put the brakes right.
Any ideas ??
No, if the pedal was fine going home then the fluid didn't boil. Boiling fluid will give you a very soft pedal.
From your description what you suffered was brake fade. Invest in better pads that will operate at higher temperatures and look also at the disks that you are using. They may be unable to dissipate the heat being generated.
From your description what you suffered was brake fade. Invest in better pads that will operate at higher temperatures and look also at the disks that you are using. They may be unable to dissipate the heat being generated.
Edited by Ianeire on Wednesday 21st May 14:02
I think if the fluid had boiled you would not get brakes back until you had bled them. I expect the pad material got too hot and stopped working effectivley. I guess you would need to get some aftermarket pads to stop this happening again. I have Ferodo DS2500 pads on the front of my car which worked well on the track but really I have no idea what would be good for a Porsche.
EDIT: curses beaten!
EDIT: curses beaten!
Edited by hifihigh on Wednesday 21st May 13:59
If it's a C2 with the small 2 pot rears (the C2s changed to 4 pots sometime in 1992 IIRC), these are likely to be the culprits for the overheating/fading. I had the same effect with mine (also at Donny strangely enough) and remedied it by fitting 4 pots (bigger pads to disperse the heat). Higher boiling point fluid and keeping it fresh also helps against fade.
haggle said:
defo boiled fluid suggest some dot 5.1 much higher boiling point, and some better pads (cant speak for porsche but pop into the porsche forum and ask)
I used to think 5.1 as well. But a lot of the racing fluids are DOT4 and go to higher temps than dot 5.1 fluids. they just dont meet other requirements for the DOT5.1 standard.Either way you definately need to refresh with a good quality high temp fluid.
Was this your first track day ever? If so, some tuition will help you use the brakes better i.e. braking a bit later but harder, then coming off the brakes quickly. Means that the pads are in contact with the discs for less time and hence less heat build up.
Otherwise, as suggested invest in some better brake fluid - even something like ATE Super Blue, which is cheaper than SRF - and pads.
Otherwise, as suggested invest in some better brake fluid - even something like ATE Super Blue, which is cheaper than SRF - and pads.
Brake fluid was boiling and possibly pads got too hot. The same happened to me on my 1st track day.
Get a better fluid (I use ATE Superblue, which has a very high wet boiling point relative to its price) and swap the pads to Pagid RS 14.
Swapping the pads is really easy and you can do it at the race track. It should take max 30 mins.
For the fluid if you have never done it it is best to take it to a shop.
120mph under the bridge with a stock C2 is quite good!!!! Well done!
Get a better fluid (I use ATE Superblue, which has a very high wet boiling point relative to its price) and swap the pads to Pagid RS 14.
Swapping the pads is really easy and you can do it at the race track. It should take max 30 mins.
For the fluid if you have never done it it is best to take it to a shop.
120mph under the bridge with a stock C2 is quite good!!!! Well done!
Perhaps One more thing in addition to better fluid and pad compound would be to do a little brake pedal test just before your normal braking zone to make sure that you have a decent pedal feel. If you happen to use the kerbs, this can sometimes lead to "pad Knock back" where the caliper pistons/retract and leave a gap to the brake discs. This problem is rare in street car brakes, but I've experienced it in my M3, but not at 120+ mph.
As it stands, it looks like you're too fast for the brakes.
m
As it stands, it looks like you're too fast for the brakes.
m
yep sounds like boiled fluid, having checked the dry boiling poojtsand usign castrol SRF as the bech mark i found AP racing PRF660 to be the closest and it is doestcost an arma anda leg eithier appro 12 quid for 0.5 ltr. I've used super racing blue as well in my old e30 M3 with some success, eurocar parts sell it by the litre. also worth fitting some pads as well like pagids et al but these wont stop the fluid boiling.
chris7676 said:
Interesting theory that braking hard will generate less heat.
Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........
Read it again. Same energy/heat released over a shorter period. = pads spend less time against disks = pads dont get so hot = pads pass less heat to the fluid. It's a thermal inertia thing I believe. Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........Edited by chris7676 on Thursday 22 May 13:01
Munter said:
chris7676 said:
Interesting theory that braking hard will generate less heat. Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........
Read it again. Same energy/heat released over a shorter period. = pads spend less time against disks = pads dont get so hot = pads pass less heat to the fluid. It's a thermal inertia thing I believe. Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........Edited by chris7676 on Thursday 22 May 13:01
chrisr29 said:
Munter said:
chris7676 said:
Interesting theory that braking hard will generate less heat. Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........
Read it again. Same energy/heat released over a shorter period. = pads spend less time against disks = pads dont get so hot = pads pass less heat to the fluid. It's a thermal inertia thing I believe. Surely all racing cars shouldnt have any need for hight temp. fluids and brakes in such a case...........Edited by chris7676 on Thursday 22 May 13:01
The level of braking is the same. The energy released is the same. But the key is reducing the ammount of time the pad is in contact with the hotter disk, thus preventing heat soak into the pad and through into the fluid.
If I wave a piece of metal through a flame with one hand pressed to the back my hand will not get hot. If I hold the metal in the flame eventually the metal will heat up and burn my hand.
Now in the case of brakes the flame in my example is at different temperatures, which does affect the ammount of time before the hand gets burnt. But hopefully you see the opportunity for something to be much hotter on one side than the other, even though in another situation the same thing with less heat would be warm all the way through.
150deg's after 2 laps cool down. I'm running DS3000 pads. Forum | Track Days | Top of Page | What's New | My Stuff