Boiled DOT 5.1- Watkins Glen @ 140MPH
09-13-2016, 04:11 PM
#21
Le Mans Master
Holy braking-zones Batman!! Where is that?Yup.
I won't touch that track without good fluid and, depending on the car, full race pads. It just eats brakes. On the upside, I've gotten pretty damn good at braking
Rumor has it, they're redoing a lot of it. Turn six will grow, like it has a tumor (bigger sweeping turn that will hook right into the straight).
I talked to the owner about it a lot. I'm hoping they do something where they replace at least one of the other double apexes with something else. Turn 3, 6, 9 and 11 are all so similar (and hell on brakes). I love the Turn 3,4,5 combo. It's just so fast into an uphill right kink braking zone. Good times. I hope it's 9 or 11 they change.
09-13-2016, 04:16 PM
#22
Le Mans Master
Think of it this way. Regardless of the weight of the car, your engine is pumping X amount of power into going faster every second you're on the gas. Your brakes need to undo that.
The same engine in a 10,000lb car and 3000lb car, WOT for the same amount of time, will need the same amount of brakes to stop it. Energy in vs out. There is no magic there. The amount of energy required to get a car to 100mph is the same as it takes to stop it, ignoring drag and friction.
Heavier cars have it worse because they are WOT longer. If you put a 1000lb anchor in your trunk, it will take you longer to get down the straight. You're WOT longer. More energy in the car. Need more brakes. So they are slower getting through the straight and they need to start braking earlier even though they are going slower.
Moral of the story: In motorsports as in life, no fatties.
Last edited by village idiot; 09-13-2016 at 04:19 PM.
09-13-2016, 05:21 PM
#23
I find most of my HPDE students are intimidated by the speeds and over-brake.
However, in a car as powerful as a C7, you need race-grade brake fluid and pads if you are going to track it at more than novice speeds.
fur sur!
09-13-2016, 06:33 PM
#24
Le Mans Master
Motul 5.1 is NOT a good track fluid!!!
It only has a dry boiling point of 522°F!
I used to use Motul RBF 600 (dry boiling pt 594°) and found it to be VERY good. Motul RBF 660 has a dry boiling pt of 617°.
So...the 5.1 isn't even close to being in the same league as the "RBF" Racing Brake Fluids!!
DOT 5 fluids are silicone based. DOT 5.1 is a designation for standard non-silicone (usually glycol ether) based fluids that conform to the boiling point, density, etc., standards of DOT 5. Some may be up to DOT 4 racing fluid standards, but as you can see with the Motul 5.1, they may really only be a very good fluid for street use.
As I said, I used to use Motul RBF 600 and found it to be excellent, but I decided to use what is arguably the best fluid available - I now use Castrol SRF. There are a couple other fluids that compare favorably with the SRF, but I've found the SRF to be really great.
The SRF dry blg pt is 594° (there are some others with higher), but the wet blg pt is 518°, and there aren't many others that are that good. That's essentially the same as the Motul 5.1 DRY blg pt!!!
Bottom line - when taking the car to the track, get a good DOT 4 racing brake fluid!!!
Just MHO, your mileage may vary!
Take a look at the Stoptech white paper bulletin on brake fluids "Brake Fluid 1A":
http://www.stoptech.com/technical-su...rs/brake-fluid
Here's a link to all the Stoptech brake system white papers - LOTS of good stuff about brakes!!!!!
http://www.stoptech.com/technical-su...l-white-papers
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09-13-2016, 06:38 PM
#25
Sr.Random input generator
You have a good point, but I always wonder about the health of seals, too. The fluids get contaminated after all from the seals, and flushing the fluid helps get rid of contaminants. This is especially true for clutch due to its design on this car.
Last edited by X25; 09-13-2016 at 06:38 PM.
09-13-2016, 08:01 PM
#26
Le Mans Master
Is our clutch and brake system all using the same fluid (as in the the same system, not specifications)?
09-13-2016, 08:05 PM
#27
Sr.Random input generator
09-13-2016, 08:09 PM
#28
Race Director
DOT 4 is the grade applicable to most race engineered brake fluid in the world today....The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption.
I've read that a lot of track hounds will leave the SRF in all season, and that's what I do. I flush in fresh SRF every spring, and do very minor bleeds after every few track days just to make sure there's fresh stuff in the calipers.
However, like it says in that quote above, DOT 4 fluids absorb more water, or maybe it's just quicker, than DOT 3.
In a street car many vehicle manufacturers recommend flushing in new DOT 3 every 2 years, but the C7 maintenance schedule says to flush in new fluid every 45,000 miles - that will be MANY YEARS for a lot of owners!!
So....DOT 4 should have fresh fluid flushed in, IMHO, at least every year - especially in a car that sees a fair amount of track time.
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09-13-2016, 08:13 PM
#29
Le Mans Master
Well the Castrol stuff is supposed to absorb less water. Also, even when it does, it's wet boiling point is so high it might not even matter. My car is a daily driver and I might do the occasional session or two. I have a dedicated track car, but sometimes I like taking the vette out.
Here's the real question: Now much brake fluid does our system need. At $70/quart, that is probably the most important question
Here's the real question: Now much brake fluid does our system need. At $70/quart, that is probably the most important question
09-13-2016, 08:32 PM
#30
Race Director
Initial flush to swap in a new type of fluid will probably take 1-1/2 liters.
After I have flushed in SRF, the next flush I use a 1 liter bottle and find that is plenty to get fresh fluid in there.
There have been a lot of threads (probably mostly in the AutoX/Roadrace section of the forum) about how long you can keep an already opened bottle of brake fluid before it's no good. I've seen 2 weeks to 6 months, with the longer periods usually only for something like SRF. After the bottle is opened and moist air has been allowed to contact the fluid, it will start absorbing water.
I wish the SRF came in 1/2 liter bottles so if I one bottle weren't enough, and I did need to open a new bottle to use just a little, I wouldn't need to crack open another full liter.
With my Motive Power Bleeder, I DO NOT put the fluid into the jug - I just use the Motive as a pressure source because any fluid that's in the jug is trash after a bleed. You can't put it back into it's original bottle and save it - throw it away!
When using the Motive as only a pressure source to push the new fluid through your brake lines, you have to be VERY CAREFUL not to run the master cylinder dry and get air down in the brake lines!! I don't bleed more than one wheel before checking the m/c and adding fluid if necessary to top it off.
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After I have flushed in SRF, the next flush I use a 1 liter bottle and find that is plenty to get fresh fluid in there.
There have been a lot of threads (probably mostly in the AutoX/Roadrace section of the forum) about how long you can keep an already opened bottle of brake fluid before it's no good. I've seen 2 weeks to 6 months, with the longer periods usually only for something like SRF. After the bottle is opened and moist air has been allowed to contact the fluid, it will start absorbing water.
I wish the SRF came in 1/2 liter bottles so if I one bottle weren't enough, and I did need to open a new bottle to use just a little, I wouldn't need to crack open another full liter.
With my Motive Power Bleeder, I DO NOT put the fluid into the jug - I just use the Motive as a pressure source because any fluid that's in the jug is trash after a bleed. You can't put it back into it's original bottle and save it - throw it away!
When using the Motive as only a pressure source to push the new fluid through your brake lines, you have to be VERY CAREFUL not to run the master cylinder dry and get air down in the brake lines!! I don't bleed more than one wheel before checking the m/c and adding fluid if necessary to top it off.
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Last edited by BEZ06; 09-13-2016 at 08:33 PM.
09-13-2016, 09:44 PM
#31
Melting Slicks
Well the Castrol stuff is supposed to absorb less water. Also, even when it does, it's wet boiling point is so high it might not even matter. My car is a daily driver and I might do the occasional session or two. I have a dedicated track car, but sometimes I like taking the vette out.
Here's the real question: Now much brake fluid does our system need. At $70/quart, that is probably the most important question
Here's the real question: Now much brake fluid does our system need. At $70/quart, that is probably the most important question
10-04-2016, 11:50 PM
#32
Le Mans Master
So our track garage owner/mechanic strongly advised against Castrol for a daily driver. He said it's not good with seals when it collects water 
10-05-2016, 01:55 AM
#33
As atmospheric water is absorbed, lowering boiling point.
In tests Castrol's ratings, both wet and dry boiling, is quite good.
10-05-2016, 02:00 AM
#34
Sr.Random input generator
I think he is thinking that the water collected would corrode the seals, etc. As far as I understand, the brake fluid does not just physically contain the water, it bonds to it. Otherwise water would easily (individually) boil at 212 degrees F or so, like it does in engine oil where it is only physically contained, which would not be acceptable for the brake system. As such, at least his reasoning sounds incorrect.
Last edited by X25; 10-05-2016 at 02:01 AM.
10-05-2016, 10:02 AM
#35
Le Mans Master
I did some more research and it seems like the Castrol eats magnesium in the brake master cylinder. I'm not sure if the C7 has magnesium in there or not, but the C5z06 does.
Also, SRF isn't THAT expensive. It's $60 for a liter. 660 is $25 for half a liter. It's basically $5 more than 660. It just sucks that you can't buy it in small "bleed my brakes" sized bottles.
Also, SRF isn't THAT expensive. It's $60 for a liter. 660 is $25 for half a liter. It's basically $5 more than 660. It just sucks that you can't buy it in small "bleed my brakes" sized bottles.
Last edited by village idiot; 10-05-2016 at 10:05 AM.
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daleong (10-05-2016)
10-05-2016, 11:39 AM
#36
If tracking car, should change VERY regularly. If not, follow GM service recommendations. 2-3% seems to be the average amount of water collected into fluids per year.
Anyone tracking/racing their car should not even THINK about it...just DO IT! First time your fluid boils and the pedal hits the floor, you'll wish you had.
Anyone tracking/racing their car should not even THINK about it...just DO IT! First time your fluid boils and the pedal hits the floor, you'll wish you had.
10-05-2016, 12:54 PM
#37
Le Mans Master
Oh, I thought I should add. My friend fills his opened brake fluid bottles up with Nitrogen (he has a big bottle in the garage). He claims it works well to keep air and moisture out.
10-05-2016, 01:43 PM
#38
Sr.Random input generator
I did some more research and it seems like the Castrol eats magnesium in the brake master cylinder. I'm not sure if the C7 has magnesium in there or not, but the C5z06 does.
Also, SRF isn't THAT expensive. It's $60 for a liter. 660 is $25 for half a liter. It's basically $5 more than 660. It just sucks that you can't buy it in small "bleed my brakes" sized bottles.
Also, SRF isn't THAT expensive. It's $60 for a liter. 660 is $25 for half a liter. It's basically $5 more than 660. It just sucks that you can't buy it in small "bleed my brakes" sized bottles.
Regarding pricing, I use RBF600 (better wet performance than RBF660), and it comes to about $14/bottle, so the price gap is there, but as you also mentioned, the problem is also with the fact that you have to ruin a liter of the fluid even for a simple bleed job.
P.S. didn't know about issues with magnesium lines and Castrol; thanks for the info.
Last edited by X25; 10-05-2016 at 01:43 PM.
10-21-2016, 03:45 PM
#39
Le Mans Master
I'm upgrading my Z51 to Z06 (iron) brakes. Wonder if I could get away with a street pad on the track. Any thoughts?
It's only 460hp...
I could just test it out on a private track day and see what happens. If it starts getting spongy, just come off and buy some pads.
It's only 460hp...
I could just test it out on a private track day and see what happens. If it starts getting spongy, just come off and buy some pads.
Last edited by village idiot; 10-21-2016 at 03:52 PM.
10-21-2016, 03:51 PM
#40
Depends on the track and your level of driving.
I took my Z to Watkins Glen and the pads I ordered were wrong, so went on stock pads. Good for a few laps, then go away fast. (I have a LOT of track driving experience, but don't need to be the fastest each day).
Hawk DTC60's and no fade at all...bite like a rabid dog!
I took my Z to Watkins Glen and the pads I ordered were wrong, so went on stock pads. Good for a few laps, then go away fast. (I have a LOT of track driving experience, but don't need to be the fastest each day).
Hawk DTC60's and no fade at all...bite like a rabid dog!
