Brake Fluid - did I cook it ?
08-30-2015, 02:55 PM
#1
Burning Brakes
Thread Starter
Brake Fluid - did I cook it ?
I run a stock 1993 corvette in HPDE, Intermediate group. It is equipped with 13 inch J55 rotors, and I use Carbotech XP 10/8 pads, with Motul 600 fluid. I also have cooling ducts delivering air directly to the center of the rotors. I have run this set up for two years with consistently good performance and no braking issues.
I religiously bleed my brakes after each track weekend, usually wasting just under a pint of fluid to remove the slightly discolored fluid and to get new fluid to the speed bleeder.
This weekend, the wasted fluid was very dark and somewhat cloudy. It took two pints to get clean fluid to the speed bleeders. This makes me think that I may have cooked the fluid. But my braking performance did not suffer.
Yesterday's track event was at Pittsburgh, on the new south track. It has a couple of notable hard braking areas, with sharp turns at the bottom of a steep downgrade. So maybe the track is harder on brakes than I am used to.
There are two other new factors to consider:
1. I caught myself mid way through my track day braking passively, with less foot pressure on the pedal, and longer duration. Once I noticed it, I used more aggressive shorter duration technique.
2. Over the last month ( and since the previous track weekend and brake fluid flush) I have used the car as a daily driver, putting about 40 miles a day on it.
I would appreciate feed back on which of these would have contributed most to the apparent increased affect on the brake fluid. If it was the track, well then - it is what it is. But if it was my braking technique or the month of daily driving, then those are both manageable.
I religiously bleed my brakes after each track weekend, usually wasting just under a pint of fluid to remove the slightly discolored fluid and to get new fluid to the speed bleeder.
This weekend, the wasted fluid was very dark and somewhat cloudy. It took two pints to get clean fluid to the speed bleeders. This makes me think that I may have cooked the fluid. But my braking performance did not suffer.
Yesterday's track event was at Pittsburgh, on the new south track. It has a couple of notable hard braking areas, with sharp turns at the bottom of a steep downgrade. So maybe the track is harder on brakes than I am used to.
There are two other new factors to consider:
1. I caught myself mid way through my track day braking passively, with less foot pressure on the pedal, and longer duration. Once I noticed it, I used more aggressive shorter duration technique.
2. Over the last month ( and since the previous track weekend and brake fluid flush) I have used the car as a daily driver, putting about 40 miles a day on it.
I would appreciate feed back on which of these would have contributed most to the apparent increased affect on the brake fluid. If it was the track, well then - it is what it is. But if it was my braking technique or the month of daily driving, then those are both manageable.
08-30-2015, 05:52 PM
#2
Safety Car
I run a stock 1993 corvette in HPDE, Intermediate group. It is equipped with 13 inch J55 rotors, and I use Carbotech XP 10/8 pads, with Motul 600 fluid. I also have cooling ducts delivering air directly to the center of the rotors. I have run this set up for two years with consistently good performance and no braking issues.
I religiously bleed my brakes after each track weekend, usually wasting just under a pint of fluid to remove the slightly discolored fluid and to get new fluid to the speed bleeder.
This weekend, the wasted fluid was very dark and somewhat cloudy. It took two pints to get clean fluid to the speed bleeders. This makes me think that I may have cooked the fluid. But my braking performance did not suffer.
Yesterday's track event was at Pittsburgh, on the new south track. It has a couple of notable hard braking areas, with sharp turns at the bottom of a steep downgrade. So maybe the track is harder on brakes than I am used to.
There are two other new factors to consider:
1. I caught myself mid way through my track day braking passively, with less foot pressure on the pedal, and longer duration. Once I noticed it, I used more aggressive shorter duration technique.
2. Over the last month ( and since the previous track weekend and brake fluid flush) I have used the car as a daily driver, putting about 40 miles a day on it.
I would appreciate feed back on which of these would have contributed most to the apparent increased affect on the brake fluid. If it was the track, well then - it is what it is. But if it was my braking technique or the month of daily driving, then those are both manageable.
I religiously bleed my brakes after each track weekend, usually wasting just under a pint of fluid to remove the slightly discolored fluid and to get new fluid to the speed bleeder.
This weekend, the wasted fluid was very dark and somewhat cloudy. It took two pints to get clean fluid to the speed bleeders. This makes me think that I may have cooked the fluid. But my braking performance did not suffer.
Yesterday's track event was at Pittsburgh, on the new south track. It has a couple of notable hard braking areas, with sharp turns at the bottom of a steep downgrade. So maybe the track is harder on brakes than I am used to.
There are two other new factors to consider:
1. I caught myself mid way through my track day braking passively, with less foot pressure on the pedal, and longer duration. Once I noticed it, I used more aggressive shorter duration technique.
2. Over the last month ( and since the previous track weekend and brake fluid flush) I have used the car as a daily driver, putting about 40 miles a day on it.
I would appreciate feed back on which of these would have contributed most to the apparent increased affect on the brake fluid. If it was the track, well then - it is what it is. But if it was my braking technique or the month of daily driving, then those are both manageable.
but I'm betting on dragging the brakes and or harder braking
08-30-2015, 08:31 PM
#3
Safety Car
I cooked DOT3 before and it was as you described it.
I run a pint thru my 93 before each track day as well. I don't bother afterwards unless I had an issue. I think fresh before is better than after as brake fluid absorbs moisture. I want it as fresh as possible. I did Nelson's and Pitt Race this year. I had no problems on either track.
We ran the full course at Pitt Race.
I was running ZII* 255/40/17's on stock Sawblades.
Ferodo DS2500's Front and Hawk HPS rear.
Wilwood 570 fluid with J55 calipers and rotors.
I DO NOT have brake cooling ducts and I had ZERO issues on either track. 3 20 minute sessions at Pitt Race.
I did run novice group but I was not putzing around. I was easily seeing 100+ on all three straights and 115+ on the long old North track back straight. I was braking late and hard but not too late. Able to keep up with a GT3 and a C5Z06 and they where not going slow. I estimate lap times in the sub 2:15 area maybe 2:10 on my best laps.
The brakes got hotter than at Nelson's but I have no idea for sure how much as I forgot my IR temp gun. They reached 350 in the pits at Nelson's after a session with cool down lap. I suspect Pitt Race might have been more like 400+ with cool down lap, IDK?
How is your car setup? Are you seeing higher speeds than I did? Other than the straights I used very little brakes in most turns. The down hill you are talking about I was going about 80ish into it and leaving about 45-50ish. I used some there but not long. If I touched my brakes in the S's it was not much.
I run a pint thru my 93 before each track day as well. I don't bother afterwards unless I had an issue. I think fresh before is better than after as brake fluid absorbs moisture. I want it as fresh as possible. I did Nelson's and Pitt Race this year. I had no problems on either track.
We ran the full course at Pitt Race.
I was running ZII* 255/40/17's on stock Sawblades.
Ferodo DS2500's Front and Hawk HPS rear.
Wilwood 570 fluid with J55 calipers and rotors.
I DO NOT have brake cooling ducts and I had ZERO issues on either track. 3 20 minute sessions at Pitt Race.
I did run novice group but I was not putzing around. I was easily seeing 100+ on all three straights and 115+ on the long old North track back straight. I was braking late and hard but not too late. Able to keep up with a GT3 and a C5Z06 and they where not going slow. I estimate lap times in the sub 2:15 area maybe 2:10 on my best laps.
The brakes got hotter than at Nelson's but I have no idea for sure how much as I forgot my IR temp gun. They reached 350 in the pits at Nelson's after a session with cool down lap. I suspect Pitt Race might have been more like 400+ with cool down lap, IDK?
How is your car setup? Are you seeing higher speeds than I did? Other than the straights I used very little brakes in most turns. The down hill you are talking about I was going about 80ish into it and leaving about 45-50ish. I used some there but not long. If I touched my brakes in the S's it was not much.
08-30-2015, 08:49 PM
#4
Pro
If you didn't experience any braking issues, you didn't boil it. That's the main thing. The fluid will get dark with moisture and heat. To Rubie's point above, the Motul fluid is great, but absorbs water (like most high temp fluids). It is best to put fresh fluid in just before an event. If you put it in a few months before, it will have absorbed a lot of water and it's max temp will be reduced.
08-31-2015, 09:31 AM
#5
Drifting
if you cooked the fluid, you may have cooked the caliper seals as well, that can turn the fluid dark with fine particles from the deteriorating seals.
Check the cover seal on the master, is it leaking air? Good idea to replace it on a car the age of yours.
Also, an overfilled system will keep a tad bit of pressure on the brakes when the fluid heats up and expands. Keep it just above the min for track service. Sometimes we swap to new pads and forget we have been following the caliper pistons out on pad wear with fluid additions.
Check the cover seal on the master, is it leaking air? Good idea to replace it on a car the age of yours.
Also, an overfilled system will keep a tad bit of pressure on the brakes when the fluid heats up and expands. Keep it just above the min for track service. Sometimes we swap to new pads and forget we have been following the caliper pistons out on pad wear with fluid additions.
08-31-2015, 04:53 PM
#6
Burning Brakes
Thread Starter
Good idea
If you didn't experience any braking issues, you didn't boil it. That's the main thing. The fluid will get dark with moisture and heat. To Rubie's point above, the Motul fluid is great, but absorbs water (like most high temp fluids). It is best to put fresh fluid in just before an event. If you put it in a few months before, it will have absorbed a lot of water and it's max temp will be reduced.
I think you are spot on. I usually have only about two weeks between events and therefore between my bleeding (immediately post event) and the next event. But this time it was six weeks.
08-31-2015, 04:56 PM
#7
Burning Brakes
Thread Starter
I didn't know that...
if you cooked the fluid, you may have cooked the caliper seals as well, that can turn the fluid dark with fine particles from the deteriorating seals.
Check the cover seal on the master, is it leaking air? Good idea to replace it on a car the age of yours.
Also, an overfilled system will keep a tad bit of pressure on the brakes when the fluid heats up and expands. Keep it just above the min for track service. Sometimes we swap to new pads and forget we have been following the caliper pistons out on pad wear with fluid additions.
Check the cover seal on the master, is it leaking air? Good idea to replace it on a car the age of yours.
Also, an overfilled system will keep a tad bit of pressure on the brakes when the fluid heats up and expands. Keep it just above the min for track service. Sometimes we swap to new pads and forget we have been following the caliper pistons out on pad wear with fluid additions.
08-31-2015, 05:12 PM
#8
Burning Brakes
Thread Starter
I cooked DOT3 before and it was as you described it.
I run a pint thru my 93 before each track day as well. I don't bother afterwards unless I had an issue. I think fresh before is better than after as brake fluid absorbs moisture. I want it as fresh as possible. I did Nelson's and Pitt Race this year. I had no problems on either track.
We ran the full course at Pitt Race.
I was running ZII* 255/40/17's on stock Sawblades.
Ferodo DS2500's Front and Hawk HPS rear.
Wilwood 570 fluid with J55 calipers and rotors.
I DO NOT have brake cooling ducts and I had ZERO issues on either track. 3 20 minute sessions at Pitt Race.
I did run novice group but I was not putzing around. I was easily seeing 100+ on all three straights and 115+ on the long old North track back straight. I was braking late and hard but not too late. Able to keep up with a GT3 and a C5Z06 and they where not going slow. I estimate lap times in the sub 2:15 area maybe 2:10 on my best laps.
The brakes got hotter than at Nelson's but I have no idea for sure how much as I forgot my IR temp gun. They reached 350 in the pits at Nelson's after a session with cool down lap. I suspect Pitt Race might have been more like 400+ with cool down lap, IDK?
How is your car setup? Are you seeing higher speeds than I did? Other than the straights I used very little brakes in most turns. The down hill you are talking about I was going about 80ish into it and leaving about 45-50ish. I used some there but not long. If I touched my brakes in the S's it was not much.
I run a pint thru my 93 before each track day as well. I don't bother afterwards unless I had an issue. I think fresh before is better than after as brake fluid absorbs moisture. I want it as fresh as possible. I did Nelson's and Pitt Race this year. I had no problems on either track.
We ran the full course at Pitt Race.
I was running ZII* 255/40/17's on stock Sawblades.
Ferodo DS2500's Front and Hawk HPS rear.
Wilwood 570 fluid with J55 calipers and rotors.
I DO NOT have brake cooling ducts and I had ZERO issues on either track. 3 20 minute sessions at Pitt Race.
I did run novice group but I was not putzing around. I was easily seeing 100+ on all three straights and 115+ on the long old North track back straight. I was braking late and hard but not too late. Able to keep up with a GT3 and a C5Z06 and they where not going slow. I estimate lap times in the sub 2:15 area maybe 2:10 on my best laps.
The brakes got hotter than at Nelson's but I have no idea for sure how much as I forgot my IR temp gun. They reached 350 in the pits at Nelson's after a session with cool down lap. I suspect Pitt Race might have been more like 400+ with cool down lap, IDK?
How is your car setup? Are you seeing higher speeds than I did? Other than the straights I used very little brakes in most turns. The down hill you are talking about I was going about 80ish into it and leaving about 45-50ish. I used some there but not long. If I touched my brakes in the S's it was not much.
Yes - I see just about the same speeds as you describe. The new south track (alone) is a bit slower in its straight (between T2 and T3), compared to the same straight on the combined track.
I first thought that the lower speeds and shorter laps might have translated into less cooling and higher brake temps. But I checked, and my pad wear was normal (about 1 mm per track day, with a track day being 3-4 sessions at 20 mins each).
So, I'm thinking it was less about temps or technique, and more about fluid age and moisture.
08-31-2015, 05:20 PM
#9
Burning Brakes
Thread Starter
I ran the combined full course on July 14, in group 2. Were you there? I will look for you in the future.
Yes - I see just about the same speeds as you describe. The new south track (alone) is a bit slower in its straight (between T2 and T3), compared to the same straight on the combined track.
I first thought that the lower speeds and shorter laps might have translated into less cooling and higher brake temps. But I checked, and my pad wear was normal (about 1 mm per track day, with a track day being 3-4 sessions at 20 mins each).
So, I'm thinking it was less about temps or technique, and more about fluid age and moisture.
Yes - I see just about the same speeds as you describe. The new south track (alone) is a bit slower in its straight (between T2 and T3), compared to the same straight on the combined track.
I first thought that the lower speeds and shorter laps might have translated into less cooling and higher brake temps. But I checked, and my pad wear was normal (about 1 mm per track day, with a track day being 3-4 sessions at 20 mins each).
So, I'm thinking it was less about temps or technique, and more about fluid age and moisture.
So, I suspect that along with age/moisture, the higher relative braking on the new short track may have contributed. Next time there, I will be sure to use fresh fluid and will be interested in seeing if I get the same degradation to the fluid.
Last edited by emptnest; 08-31-2015 at 05:28 PM.
I know SRF is great stuff but I like to bleed a complete flush just before each event. Therefore, I simply use a good DOT4.
08-31-2015, 08:41 PM
#12
Drifting
I have a C5 and I fill just to the seam in the reservoir, which is halfway between max and min.
If you do this much, you will and should be more concerned about the whoa pedal than the go pedal. Races are won in the braking zones and the turns, not the straights.
The reason you want to bleed just before going out is that if you do boil the fluid, you will have vapor bubbles (brake fluid vapor that is) and those little bubbles will not condense back and give you a mushy pedal.
You are more likely to boil when you get harder on the brakes as your experience level goes up, and when your pads wear and the heat transfer path from pad to caliper is shorter. The pad material is not a good heat conductor, but the pad backing and the pistons are!