Brake pedal gets soft but no bubbles in fluid
07-30-2014, 09:41 PM
#16
Followed by:
Not to be mean, but you have to notice the irony. Made me laugh, anyway. 
-Mike
you are dragging the brakes too much going into turn 2 would be my guess. you cant slow a car going 125 at the #3 marker with street tires and make a turn at a speed that street tires could hold on to.
if you could brake that late and fast, your lap times would have to be 1:45.
Maybe they are.
generally, street tires tend to make you brake a little earlier and drag the brakes a little longer. When i instruct, I see this all the time. cant tell you off all the guys , even that ive race with that see a soft pedal and are going 5 seconds slower a lap with a less hp, lighter car..... its also possible that you had to slow to a much slower speed to make turn 2 turn in speed on street tires, and a heavy car.
pagid yellows are endurance pads, but race pads and should work fine. (equal to pagid orange, so fine for you performance level).
superblue, as crappy as everyone says it is, ive race on and raced to some pretty fast laps, 136.1 over 50min races, and not changed fluid for multiple weekends. it has a lower wet and dry boiling point. but as someone said already, the boiling point to use is the wet, once you crack the bottle open.
you could have had air in the line. just because you have no bubbles that you can see, doesnt mean there isnt any air in the line or in the calipers,and crossovers. they blend together as water does on concrete.
I changed fluid because of all the hype for stoptech fluid, and Castrol, and others.( motul, torque, etc)
it will help, but probably you have just cooked the fluid. sounds like you bled them and it fixed the problem.... maybe problem gone now.
definitely not the lines..... those thick rubber lines done balloon up. its a misconception that they do. they are fine until they fatigue and crack and blow a hole out the side. the braided lines help this problem, but also braided lines are metal mesh and they weaken up front with the steering bending them back and forth on every turn. better trade off to go with braided steel lines but i and others have raced successfully with rubber lines.. (until mine exploded after 20 years) if they are not leaking or look old, they are not the issue.
those are better for sure, but he should be just fine on the blue.
bubbles can occure, if you boil the fluid.. they will sometimes appear when you bleed the lines. sometimes they group together and can come out as gaps in the fluid. hygroscopically, each of the fluid manufacturers make formulas to resist absorbing water from the air. some are better than others.
you probably couldnt see them. there could be large air gaps formed by boiling the fluid, which happens at 400 degrees or so at the caliper. disolved water in the fluid also can make this much worse and lower the boiling point substantially.
people always mock what they dont understand.
its actually quite simple. He boiled the brake fluid. street tires and his hp/weight wouldnt allow him to exceed the abilities of the brake rotors and pads. And, mike, to your funny point above, its is about KE of the car and the brake systems ability to shed heat. a stock car on DOTs or a street tire, should be able to get a day out of the race pads and superblue without issue. yes, cooling, and better fluid always helps.
if he has a lap on video, we can check it out to see if there is any technique to reduce the load on the brakes.
if you could brake that late and fast, your lap times would have to be 1:45.
Maybe they are.
generally, street tires tend to make you brake a little earlier and drag the brakes a little longer. When i instruct, I see this all the time. cant tell you off all the guys , even that ive race with that see a soft pedal and are going 5 seconds slower a lap with a less hp, lighter car..... its also possible that you had to slow to a much slower speed to make turn 2 turn in speed on street tires, and a heavy car.
pagid yellows are endurance pads, but race pads and should work fine. (equal to pagid orange, so fine for you performance level).
superblue, as crappy as everyone says it is, ive race on and raced to some pretty fast laps, 136.1 over 50min races, and not changed fluid for multiple weekends. it has a lower wet and dry boiling point. but as someone said already, the boiling point to use is the wet, once you crack the bottle open.
you could have had air in the line. just because you have no bubbles that you can see, doesnt mean there isnt any air in the line or in the calipers,and crossovers. they blend together as water does on concrete.
I changed fluid because of all the hype for stoptech fluid, and Castrol, and others.( motul, torque, etc)
it will help, but probably you have just cooked the fluid. sounds like you bled them and it fixed the problem.... maybe problem gone now.
definitely not the lines..... those thick rubber lines done balloon up. its a misconception that they do. they are fine until they fatigue and crack and blow a hole out the side. the braided lines help this problem, but also braided lines are metal mesh and they weaken up front with the steering bending them back and forth on every turn. better trade off to go with braided steel lines but i and others have raced successfully with rubber lines.. (until mine exploded after 20 years) if they are not leaking or look old, they are not the issue.
those are better for sure, but he should be just fine on the blue.
bubbles can occure, if you boil the fluid.. they will sometimes appear when you bleed the lines. sometimes they group together and can come out as gaps in the fluid. hygroscopically, each of the fluid manufacturers make formulas to resist absorbing water from the air. some are better than others.
you probably couldnt see them. there could be large air gaps formed by boiling the fluid, which happens at 400 degrees or so at the caliper. disolved water in the fluid also can make this much worse and lower the boiling point substantially.
people always mock what they dont understand.
its actually quite simple. He boiled the brake fluid. street tires and his hp/weight wouldnt allow him to exceed the abilities of the brake rotors and pads. And, mike, to your funny point above, its is about KE of the car and the brake systems ability to shed heat. a stock car on DOTs or a street tire, should be able to get a day out of the race pads and superblue without issue. yes, cooling, and better fluid always helps.
if he has a lap on video, we can check it out to see if there is any technique to reduce the load on the brakes.
-Mike
07-30-2014, 09:47 PM
#17
Rennlist Member
Thread Starter
Thanks for all the info :-)
to quickly answer a few questions/assumptions:
1:45 lap times on Nitto NT-01
PDK is on (blush), I got so annoyed with the god-damn "kickdown downshift" that you can't turn off (you go into turn 3 in 3rd gear, PDK downshifts mid-turn to 2nd , you don't notice, think you still in 3rd and hit the limiter between 3 and 4), so that I left PDK on "Auto"
here's a video, not from last weekend, but from a couple weeks ago
to quickly answer a few questions/assumptions:
1:45 lap times on Nitto NT-01
PDK is on (blush), I got so annoyed with the god-damn "kickdown downshift" that you can't turn off (you go into turn 3 in 3rd gear, PDK downshifts mid-turn to 2nd , you don't notice, think you still in 3rd and hit the limiter between 3 and 4), so that I left PDK on "Auto"
here's a video, not from last weekend, but from a couple weeks ago
07-30-2014, 09:56 PM
#19
Rennlist Member
07-30-2014, 09:59 PM
#20
Rennlist Member
Hey, pretty good ... i guessed your lap time within .4 seconds. (based on your experience, tone of the email, and the car) off a little bit due to you running on DOTs. i bet we fix your braking problem, and we get you down to 1:42.
if thats bruce and Rob Todd in the white GT3, I used to race with these guys years ago!
good guys! BRracing!
(based on your experience, tone of the email, and the car) off a little bit due to you running on DOTs. i bet we fix your braking problem, and we get you down to 1:42. if thats bruce and Rob Todd in the white GT3, I used to race with these guys years ago!
good guys! BRracing!
07-30-2014, 10:13 PM
#21
Rennlist Member
looks good. 115mph into turn 2 though.
double apex of turn 2 good. get on the gas a little earlier
get wider for entry of turn 3, making more of a turn than need be
turn 4 good, but get on gas much earlier
turn 5 good too. dont know if you need downshift to 2nd. hit a little faster, its banked and lots of grip with a big exit.
turn 6. you can hit this at 75mph, not 70 with no issues, but work up to it. try and and turn in earlier with less steering input to make less of a turn out of it. lots of time lost there, especially with the big climb to the corkscrew.
good braking into the corkscrew entrance. bad line out, forces much more of a turn out of it. notice how you kind of "cllunk" at the apex??? should be smooth there by turning into the turn earlier, so you are pullling lateral gs through the turn, and not drivng through it. turn before, during and after, and you will be a lot faster thought it.
good exit out into 9, no brake tap.... good job,
on the gas earlier
and then, think of 9 to 10 as a big "S", not a turn straight and then straight and then turn. get on the gas at the exit of the 9, get up high to the paddock turnoff area and immediately start to turn in to turn 10 with a quick stab for slow down. (kind of a trail brake stab as you just start to turn right)
turn 11, you late brake , but over brake, need to back off a little , to get a good line through turn 11. time lost there too, and on the exit because of that.
nice lap!
Love all the info on the video. good stuff!
is that BRracing's supercup car or their Gt3 conversion?
double apex of turn 2 good. get on the gas a little earlier
get wider for entry of turn 3, making more of a turn than need be
turn 4 good, but get on gas much earlier
turn 5 good too. dont know if you need downshift to 2nd. hit a little faster, its banked and lots of grip with a big exit.
turn 6. you can hit this at 75mph, not 70 with no issues, but work up to it. try and and turn in earlier with less steering input to make less of a turn out of it. lots of time lost there, especially with the big climb to the corkscrew.
good braking into the corkscrew entrance. bad line out, forces much more of a turn out of it. notice how you kind of "cllunk" at the apex??? should be smooth there by turning into the turn earlier, so you are pullling lateral gs through the turn, and not drivng through it. turn before, during and after, and you will be a lot faster thought it.
good exit out into 9, no brake tap.... good job,
on the gas earlier
and then, think of 9 to 10 as a big "S", not a turn straight and then straight and then turn. get on the gas at the exit of the 9, get up high to the paddock turnoff area and immediately start to turn in to turn 10 with a quick stab for slow down. (kind of a trail brake stab as you just start to turn right)
turn 11, you late brake , but over brake, need to back off a little , to get a good line through turn 11. time lost there too, and on the exit because of that.
nice lap!
Love all the info on the video. good stuff!
is that BRracing's supercup car or their Gt3 conversion?
07-30-2014, 10:30 PM
#22
You are over thinking it and confusing two separate issues.
"Boiling" brake fluid will not give you visible air/bubbles when you bleed the brakes. Bubbles are caused by introducing air into the system from the outside.
Your brakes got better after you bled them because you brought fresh(er) fluid down into the calipers.
"Boiling" brake fluid will not give you visible air/bubbles when you bleed the brakes. Bubbles are caused by introducing air into the system from the outside.
Your brakes got better after you bled them because you brought fresh(er) fluid down into the calipers.
07-31-2014, 01:41 AM
#23
Rennlist Member
Thread Starter
looks good. 115mph into turn 2 though.
double apex of turn 2 good. get on the gas a little earlier
get wider for entry of turn 3, making more of a turn than need be
turn 4 good, but get on gas much earlier
turn 5 good too. dont know if you need downshift to 2nd. hit a little faster, its banked and lots of grip with a big exit.
turn 6. you can hit this at 75mph, not 70 with no issues, but work up to it. try and and turn in earlier with less steering input to make less of a turn out of it. lots of time lost there, especially with the big climb to the corkscrew.
good braking into the corkscrew entrance. bad line out, forces much more of a turn out of it. notice how you kind of "cllunk" at the apex??? should be smooth there by turning into the turn earlier, so you are pullling lateral gs through the turn, and not drivng through it. turn before, during and after, and you will be a lot faster thought it.
good exit out into 9, no brake tap.... good job,
on the gas earlier
and then, think of 9 to 10 as a big "S", not a turn straight and then straight and then turn. get on the gas at the exit of the 9, get up high to the paddock turnoff area and immediately start to turn in to turn 10 with a quick stab for slow down. (kind of a trail brake stab as you just start to turn right)
turn 11, you late brake , but over brake, need to back off a little , to get a good line through turn 11. time lost there too, and on the exit because of that.
nice lap!
Love all the info on the video. good stuff!
is that BRracing's supercup car or their Gt3 conversion?
double apex of turn 2 good. get on the gas a little earlier
get wider for entry of turn 3, making more of a turn than need be
turn 4 good, but get on gas much earlier
turn 5 good too. dont know if you need downshift to 2nd. hit a little faster, its banked and lots of grip with a big exit.
turn 6. you can hit this at 75mph, not 70 with no issues, but work up to it. try and and turn in earlier with less steering input to make less of a turn out of it. lots of time lost there, especially with the big climb to the corkscrew.
good braking into the corkscrew entrance. bad line out, forces much more of a turn out of it. notice how you kind of "cllunk" at the apex??? should be smooth there by turning into the turn earlier, so you are pullling lateral gs through the turn, and not drivng through it. turn before, during and after, and you will be a lot faster thought it.
good exit out into 9, no brake tap.... good job,
on the gas earlier
and then, think of 9 to 10 as a big "S", not a turn straight and then straight and then turn. get on the gas at the exit of the 9, get up high to the paddock turnoff area and immediately start to turn in to turn 10 with a quick stab for slow down. (kind of a trail brake stab as you just start to turn right)
turn 11, you late brake , but over brake, need to back off a little , to get a good line through turn 11. time lost there too, and on the exit because of that.
nice lap!
Love all the info on the video. good stuff!
is that BRracing's supercup car or their Gt3 conversion?
07-31-2014, 01:48 AM
#24
Rennlist Member
Thread Starter
OK,
let me summarize what I think has crystallized so far:
a) Pads are OK, and most likely ATE Superblue is OK (hey I still have 4 cans in my garage (bought them before it got banned), this better be good ;-)
b) I probably had micro bubbles in the fluid, so when I bled they were flushed out and the world was good again
c) I need more cooling to the brakes, that IS a problem: I had already ordered the GT3 ducts and they are actually SMALLER as the ducts that came from the factory (yes the C4S is s stupid-heavy car)
So what now? GT2 ducts?
d) It's not the rubber brake hoses, so no braided steel hoses needed
e) not too muck criticism on my driving style (but I appreciate all the hints, because next track day, I want to see a 1:44 or 1:43) - I will post a video with single apex in turn 2 and higher entry speed into 2
f) anything else?
let me summarize what I think has crystallized so far:
a) Pads are OK, and most likely ATE Superblue is OK (hey I still have 4 cans in my garage (bought them before it got banned), this better be good ;-)
b) I probably had micro bubbles in the fluid, so when I bled they were flushed out and the world was good again
c) I need more cooling to the brakes, that IS a problem: I had already ordered the GT3 ducts and they are actually SMALLER as the ducts that came from the factory (yes the C4S is s stupid-heavy car)
So what now? GT2 ducts?
d) It's not the rubber brake hoses, so no braided steel hoses needed
e) not too muck criticism on my driving style (but I appreciate all the hints, because next track day, I want to see a 1:44 or 1:43) - I will post a video with single apex in turn 2 and higher entry speed into 2
f) anything else?
07-31-2014, 02:40 AM
#25
Rennlist Member
Very impressive Chris. What are your thoughts on the double apex on turn 2?
07-31-2014, 03:18 AM
#26
Rennlist Member
Plus, because of its hygroscopic qualities, the fliuid can absorb moisture (water vapor) out of the air. you cant see it, but what it does is lower the boiling point of the fluid. superblue is more susceptible to that, and has a lower boiling point wet and dry vs the higher end fluids. try stoptech, its not too expensive compared to SRF, or Torque, and stilll is well over the boiling points of ATE.OK,
let me summarize what I think has crystallized so far:
a) Pads are OK, and most likely ATE Superblue is OK (hey I still have 4 cans in my garage (bought them before it got banned), this better be good ;-)
b) I probably had micro bubbles in the fluid, so when I bled they were flushed out and the world was good again
c) I need more cooling to the brakes, that IS a problem: I had already ordered the GT3 ducts and they are actually SMALLER as the ducts that came from the factory (yes the C4S is s stupid-heavy car)
So what now? GT2 ducts?
d) It's not the rubber brake hoses, so no braided steel hoses needed
e) not too muck criticism on my driving style (but I appreciate all the hints, because next track day, I want to see a 1:44 or 1:43) - I will post a video with single apex in turn 2 and higher entry speed into 2
f) anything else?
let me summarize what I think has crystallized so far:
a) Pads are OK, and most likely ATE Superblue is OK (hey I still have 4 cans in my garage (bought them before it got banned), this better be good ;-)
b) I probably had micro bubbles in the fluid, so when I bled they were flushed out and the world was good again
c) I need more cooling to the brakes, that IS a problem: I had already ordered the GT3 ducts and they are actually SMALLER as the ducts that came from the factory (yes the C4S is s stupid-heavy car)
So what now? GT2 ducts?
d) It's not the rubber brake hoses, so no braided steel hoses needed
e) not too muck criticism on my driving style (but I appreciate all the hints, because next track day, I want to see a 1:44 or 1:43) - I will post a video with single apex in turn 2 and higher entry speed into 2
f) anything else?
do a few of the things i mention, with turn 6 being the most influential, you should see a second there, and maybe an additional second with some of the rest as well.
I think the C4S is pretty normal as far as street sport car weight. 3300, i would think. those brakes and pads should certainly handle it. if, you go back to the braking debate.
, you can do the KE calculation and see that the 115mph top speed, is a big reduction to the KE, even though you have 300lbs more weight...... possibly 500lbs with you in the car. You might have solved it with the brake bleed you did. If you are not having issues with braking into turn2, you might approach turn 11, by braking a little earlier and harder, and shorter. because you didnt have the problem after the bleed, you might have just had some air in the system. easy to do.
I guess this means there are trade offs.
07-31-2014, 09:21 AM
#27
The Penguin King
Rennlist Member
Rennlist Member
Change your brake fluid to Motul 600 or Castrol SRF. That should cure it. You could add some cooling too for good measure.
ATE isn't crap. It just doesn't have a high enough wet boiling temperature for serious track usage in some cars. Which makes it crap for some applications. ;-)
ATE isn't crap. It just doesn't have a high enough wet boiling temperature for serious track usage in some cars. Which makes it crap for some applications. ;-)
07-31-2014, 09:26 AM
#28
Rennlist Member
In regards to the OP's problem, in my experience, overheating brake fluid does not always reliably produce visible air bubbles when bleeding.
The absence of air bubbles does not mean you haven't exceeded the capabilities of your brake fluid.
07-31-2014, 10:50 AM
#29
Rennlist Member
Thread Starter
I think that the single apex is an itsy-bitsy faster, but the dual apex "feels" much faster and is much more fun.
Also you break a little earlier for the dual apex, meaning the car is a little slower than when starting breaking for single apex. So this would probably help with my brake problem.
07-31-2014, 02:08 PM
#30
Three Wheelin'
I think you are pointed in the right direction with your braking system.
It may be highly beneficial to do whatever you can to get more cooling to the front brakes. I am not familiar with the opportunities one has for water-cooleds, but there are many in our area that have experience with driving at Laguna Seca in cars that are more or less in street trim. In my experience, the highest concentration of experience is amongst PCA members that do a lot of events.
If the majority of folks running similar cars in our area are using a different fluid, that can be a clue as well. By now, the local "herd" has probably identified something that works. Perhaps more than one choice. Ate Blue may or may not be among them.
As for driving tips, I haven't watched your video, but I hope you are leveraging all of the local resources you can. In my experience, internet video critiques can help with ideas regarding car placement, but advice on when/how to get on and off the throttle and brakes can be dodgy. I believe that these things are best done in person.
I still believe that the best "home base" for Porsche drivers to work on the craft in our area is PCA, particularly the GGR. These events usually have the highest percentage of entrants keenly interested in improving. Being in an environment on the track and in the paddock where almost everyone is focused on the craft as opposed to simply the experience can pay big dividends. Talking about subtleties and trade-offs can be more helpful than talking about that GTR you were able to catch and pass.
Many other groups have great events, and I have instructed in many of these groups and know the organizers and owners of quite a few. What I have observed through a couple of decades of track driving, racing and instructing in this area is that Porsche folks with a keen interest in improving toward safe, fun, consistent and extensive use of their Porsche's performance capabilities do best with a solid foundation provided by PCA events. They usually thrive when they drive with other groups and/or graduate to wheel-to-wheel racing.
It may be highly beneficial to do whatever you can to get more cooling to the front brakes. I am not familiar with the opportunities one has for water-cooleds, but there are many in our area that have experience with driving at Laguna Seca in cars that are more or less in street trim. In my experience, the highest concentration of experience is amongst PCA members that do a lot of events.
If the majority of folks running similar cars in our area are using a different fluid, that can be a clue as well. By now, the local "herd" has probably identified something that works. Perhaps more than one choice. Ate Blue may or may not be among them.
As for driving tips, I haven't watched your video, but I hope you are leveraging all of the local resources you can. In my experience, internet video critiques can help with ideas regarding car placement, but advice on when/how to get on and off the throttle and brakes can be dodgy. I believe that these things are best done in person.
I still believe that the best "home base" for Porsche drivers to work on the craft in our area is PCA, particularly the GGR. These events usually have the highest percentage of entrants keenly interested in improving. Being in an environment on the track and in the paddock where almost everyone is focused on the craft as opposed to simply the experience can pay big dividends. Talking about subtleties and trade-offs can be more helpful than talking about that GTR you were able to catch and pass.
Many other groups have great events, and I have instructed in many of these groups and know the organizers and owners of quite a few. What I have observed through a couple of decades of track driving, racing and instructing in this area is that Porsche folks with a keen interest in improving toward safe, fun, consistent and extensive use of their Porsche's performance capabilities do best with a solid foundation provided by PCA events. They usually thrive when they drive with other groups and/or graduate to wheel-to-wheel racing.