Learn me about brake fluid

Had to cut short a track day because halfway through the third session, I cooked my brake fluid. No harm done beyond a minor scare (why is my car not slowing down?!?!) and losing track time. Yeah, I should have replaced it before the event, it had been a year already... 

Is it worth the $$$/effort to use name brand fluid (my instructor recommended Motul 600 or 660)? Or will a generic DOT4, replaced before each track day, be adequate? 

Car is a 2009 Mazdaspeed3. It's my summertime daily driver, and I do 2-4 autocross events and 2 track days per year.

If you’re only doing two track days a year then replace with a racing fluid right before the event because that’s really when you need fresh fluids. Autox isnt going to tax them and you have the rest of the year to have them collect water. If you’re paying for track time you should not run the risk of having it cut short bc you skimped on brake fluid. My opinion at least. 

Are you sure it was the fluid?  If the pedal goes to the floor, then you boiled the fluid.  If it stays firm but the car just doesn't stop as much as it's supposed to, then you overheated the pads.  Your description sounds a bit more like the second one?

As for brake fluids, IMHO generic DOT4 is not adequate for any car that goes to the track and should be replaced with a good high-temp racing fluid (and after that flushed every 6-12 months).  ATE Type 200, the Motuls, Wilwood fluid -- there are a bunch of them available.

I'd get the ate 200, last I checked Amazon had it for like $15/liter.

Annoying it's generally not for sale at the local AutoZone, but Amazon 2 day is almost as good.

codrus said:

As for brake fluids, IMHO generic DOT4 is not adequate for any car that goes to the track and should be replaced with a good high-temp racing fluid (and after that flushed every 6-12 months).  ATE Type 200, the Motuls, Wilwood fluid -- there are a bunch of them available.

This is pretty much what I do, no problems so far.

is expensive brake fluid cheaper than your collision insurance deductible?  ;-)

srsly, that's the same question i ask people who say winter tires are too expensive / inconvenient to store / swap / etc.

codrus said:

Are you sure it was the fluid?  If the pedal goes to the floor, then you boiled the fluid.  If it stays firm but the car just doesn't stop as much as it's supposed to, then you overheated the pads.  Your description sounds a bit more like the second one?

Hmm... Maybe. 

This has happened twice. I was clueless for my first track day and didn't change the fluid. The brakes faded halfway into my second session. Second track day, the organizers emphasized fresh brake fluid, so I changed it just before the event and the brakes lasted all day. And third event, as described, my brakes lasted two and a half sessions. 

As for symptoms, it came on suddenly (braking was fine, then all of a sudden it wasn't) and was a combination of what you described. The pedal went down farther (but not all the way) and the car didn't stop as much.

Based on your descriptions, I'm inclined to go for a more aggressive set of pads and replace the fluid with one of the brands suggested in this thread. (My last instructor - in the car with me when this happened - recommended Motul.) 

A. Is this overkill?
B. If not, what pads would be good for both street and limited  track + autoX?

AngryCorvair said:

is expensive brake fluid cheaper than your collision insurance deductible?  ;-)

srsly, that's the same question i ask people who say winter tires are too expensive / inconvenient to store / swap / etc.

There was the winter I left the track/autoX tires on my beloved Neon ACR through the first two snowstorms. In the first storm, I did a 180 braking for a stoplight and slid backwards onto the shoulder. In the second storm, I couldn't get enough traction to get out of my driveway. I got all-season tires on it right quick after that. 

danl318 said:

codrus said:

Are you sure it was the fluid?  If the pedal goes to the floor, then you boiled the fluid.  If it stays firm but the car just doesn't stop as much as it's supposed to, then you overheated the pads.  Your description sounds a bit more like the second one?

Hmm... Maybe. 

This has happened twice. I was clueless for my first track day and didn't change the fluid. The brakes faded halfway into my second session. Second track day, the organizers emphasized fresh brake fluid, so I changed it just before the event and the brakes lasted all day. And third event, as described, my brakes lasted two and a half sessions. 

As for symptoms, it came on suddenly (braking was fine, then all of a sudden it wasn't) and was a combination of what you described. The pedal went down farther (but not all the way) and the car didn't stop as much.

Based on your descriptions, I'm inclined to go for a more aggressive set of pads and replace the fluid with one of the brands suggested in this thread. (My last instructor - in the car with me when this happened - recommended Motul.) 

A. Is this overkill?
B. If not, what pads would be good for both street and limited  track + autoX?

A) It is not overkill.  IMHO, having a good solid set of brakes is the most important thing you can do to prep the car for track days.  There's a nice, comprehensive comparison of fluids here:

https://www.lelandwest.com/brake-fluid-comparison-chart.cfm

The most common ones you'll find people using around here are ATE Type 200 (formerly super blue, but DOT banned the blue dye, so now it's amber instead), Motul RBF600, and Castrol SRF.  That's in increasing order of cost and of boiling point.  I'd suggest starting with ATE and working up if you have have problems.

B) Brake pads are a very personal thing, for any given pad you'll find people who love it and people who hate it.  Personally, I use Hawk DTC-60s for the track and the Wilwood BP-20s for the street & autox.  Trying to combine street and track into one set of pads is something that doesn't work very well, IME, because the two regimes are so different in terms of requirements.

bcp2011 said:

If you’re only doing two track days a year then replace with a racing fluid right before the event because that’s really when you need fresh fluids. Autox isnt going to tax them and you have the rest of the year to have them collect water. If you’re paying for track time you should not run the risk of having it cut short bc you skimped on brake fluid. My opinion at least. 

This is the best answer.  I've run Valvoline synthetic in all my autocross cars, but I'll always flush and refill before a track day.  You don't need 600 degree brake fluid unless your in a real race car.  

First time I went to Atlanta Motorsports Park there was a guy there with a boosted 240sx that cut the 1st session short because the wire fell off the oil pressure sensor. He cut the second session short because he boiled the brake fluid.  I went over to help him flush and fill the system so he could get in a good session and I ended up using vice-grips to get the bleeders open.  I'm sure he spent several thousand on the turbo setup and $20 in brake fluid wouldn't break the bank.  He just didn't understand, but I explained it to him. 

Looks like there are two new items on my to-do list:

1. Learn how to bleed/flush brake fluid.

2. Re-learn how to replace brake pads. 

I've seen folks swapping pads in the paddock at track days, now I understand why.

My first event at the FIRM back in April, I ended up cooking the pads, not the fluid.

It sounds a lot like what Codrus mentions as I was running fairly fresh fluid (new fluid from a week prior), pedal felt fine, but car didn't want to stop.  When I took my pads off I saw how badly they were burned up.

Lesson learned, don't run stock brake pads on your first event thinking you'll take it easy lol

I'm a believer in spending the extra on Castrol SRF.  It has a wet boiling point (518F) higher than most dry boiling points.  That's perfect for a car that gets flushed once a year instead of before every track event.

I just found a high temp fluid that Advanced Auto had on the shelf. The brand is Pentosin, DOT4/ LV. It has almost the same boiling point as ATE and it might be easier to find in local parts stores. Decent track pads will help considerably as well, they are easy enough to swap out a couple of times a year, get a spare set of rotors as well.

Try Hawk HP plus and if they're not enough, go to the Hawk HPS.  The dust like a mofo but boy do they stop!  Our S2k has HPS pads on it and we're going to downgrade at the end of the season because we're losing momentum on the autocross course just touching them.

red_stapler said:

I'm a believer in spending the extra on Castrol SRF.  It has a wet boiling point (518F) higher than most dry boiling points.  That's perfect for a car that gets flushed once a year instead of before every track event.

For what the SRF costs to change once a year, I can flush the Motul RBF 600 3x per year. If you flush frequently the wet point is much less important, and fresh fluids prevent things from getting gummed up and gross (and gets any absorbed water out of the lines as well). 

djsilver said:

Try Hawk HP plus and if they're not enough, go to the Hawk HPS.  The dust like a mofo but boy do they stop!  Our S2k has HPS pads on it and we're going to downgrade at the end of the season because we're losing momentum on the autocross course just touching them.

HPS have a lower Mu factor and a lower and narrower temperature range.

The only thing I have to add is that the Motive pressure brake bleeder is worth its weight in gold, and almost makes bleeding brakes into a fun job.  I bleed them more often now that I have the right tool.

Hi

I asked this before  but there seems to be new people this time , 

Does the brake fluid  overheat just in the caliper or all the way up to the Master ?

Does new fluid mix with the old fluid or does the new stuff sit on top of the  old stuff ?

How does the water get in the fluid ?? Thru the cap or thru the rubber brake lines ?

When bleeding how do you know that you changed all out of that side from master to the brake caliper ?  change of color or ????

I guess thats all the questions for the morning  :)

Thanks for your ideas......

californiamilleghia said:

Hi

I asked this before  but there seems to be new people this time , 

Does the brake fluid  overheat just in the caliper or all the way up to the Master ?

Does new fluid mix with the old fluid or does the new stuff sit on top of the  old stuff ?

How does the water get in the fluid ?? Thru the cap or thru the rubber brake lines ?

When bleeding how do you know that you changed all out of that side from master to the brake caliper ?  change of color or ????

I guess thats all the questions for the morning  :)

Thanks for your ideas......

Brake fluid overheats mainly in the caliper. Some purpose-built race cars have a recirculating brake fluid system to prevent fluid from boiling this way.

If you add new fluid on top of old fluid, the new fluid will pretty much just sit on top. This is why you have to bleed the new brake fluid through completely.

Water gets into the fluid mainly through the MC reservoir cap.

You can tell when the system is fully bled by the change of color, or you can just overdo it so that you can be pretty sure you've swapped out all the fluid...back when ATE Super Blue was available, you could easily see the change from old blue fluid to new golden fluid or vice-versa.

danl318 said:

A. Is this overkill?
B. If not, what pads would be good for both street and limited  track + autoX?

A. It's not overkill

B. Depends on the car. EBC Yellowstuff works well on my mixed-use AE92, and it's been found to work well on a mixed-use Lotus Esprit, so it should work well on your MS3 as well.

I'm a Motul fan, there is a difference between various DOT 4 fluids, look up the dry and wet boiling points online if you're unsure.  For a dual purpose pad I like the StopTech Sports.  On the track as you get better/tires get stickier you'll start to go through them quickly at which point you'll want to swap between a purpose street pad and a purpose track pad. 

GameboyRMH said:

californiamilleghia said:

Hi

I asked this before  but there seems to be new people this time , 

Does the brake fluid  overheat just in the caliper or all the way up to the Master ?

Does new fluid mix with the old fluid or does the new stuff sit on top of the  old stuff ?

How does the water get in the fluid ?? Thru the cap or thru the rubber brake lines ?

When bleeding how do you know that you changed all out of that side from master to the brake caliper ?  change of color or ????

I guess thats all the questions for the morning  :)

Thanks for your ideas......

Brake fluid overheats mainly in the caliper. Some purpose-built race cars have a recirculating brake fluid system to prevent fluid from boiling this way.

If you add new fluid on top of old fluid, the new fluid will pretty much just sit on top. This is why you have to bleed the new brake fluid through completely.

Water gets into the fluid mainly through the MC reservoir cap.

You can tell when the system is fully bled by the change of color, or you can just overdo it so that you can be pretty sure you've swapped out all the fluid...back when ATE Super Blue was available, you could easily see the change from old blue fluid to new golden fluid or vice-versa.

Interesting questions, and it's interesting learning.  However, something seems inconsistent here... 

If moisture gets into the system via the MC cap, and fluids do not mix, then for both of those statements to be true then the water molecules have to travel to the calipers when the brake fluids do not.  Is this actually true? 

At first glance it seems unlikely, but I have no proof that this does or does not happen.  It would appear more intuitive to think that the moisture either gets in closer to the calipers or that the brake fluids mix.  However, my experience with ATE Blue also suggests that the brake fluids didn't really mix.  Interested to hear some opinions or references for why water molecules would travel through brake fluids.  

In reply to bcp2011 :

Water is heavier than oil so the water molecules go towards the bleeders due to gravity?

Not sure if that's exactly how it works, but it makes sense to my small brain.

it does make some sense that moisture could spread throughout the brake fluid even if the brake fluid doesn't really mix throughout the system (diffusion effect?), especially since brake fluid is hygroscopic (new fluid sucks moisture out of old fluid where they meet). This should also prevent pooling at the calipers, at least until the brake fluid is saturated.