Soft pedal after almost every track day

[Earendil]

I've done 4 track days so far this year, and after almost every one I end up with a much softer pedal by the end of the day, regardless of the brake temps. This is the sort of problem I can feel driving home. The one time I didn't change the fluid immediately before an event, was after my first HPDE of the year (it was raining hard, rarely used brakes), but by the end of my second HPDE I don't think I could lock my tires up. Since then I've changed fluid before every event and have survived.

Completely flushing the brake fluid (using superblue) makes the pedal feel a lot better. Not to anything you'd call the firmest pedal in the world, but safe feeling. The fluid seems to me the issue, but what is causing the issue?

What concerns me is that I can do a flush, and during the course of a track day I can feel the brakes getting worse. While I know regular changes are advised, certainly the guys doing enduros aren't changing brake fluid every hour or two? I'm not even a heavy brake user. I'm still focusing on other areas of my technique and using slow-in-fast-out. I rarely brake past 80% of the car's ability. I'm moderately concerned that the day I start doing the local tracks at 90+% that my brakes won't last the day.

So what might be killing my fluid? Or perhaps exaggerating the feel of bad fluid? Remember, the issue continues after the brakes have cooled off, and doesn't ever improve. Thanks for any sage wisdom you guys can provide! :)

In case it matters:

• Hawk+ pads front and back
• Blank rotors
• Calipers rebuilt 6 track days ago.
• Z2 tires (When I say I can't lock the wheels, these are them)
• SuperBlue or Type 200 (alternating)
• SS lines installed 6 track days ago
• Hard brake lines are original.
• No brake cooling.

[athayer187]

Hawk+ pads front and back
SuperBlue or Type 200 (alternating)

These are your two issues. I would recommend ducting and/or better fluid. I like Motul RBF 600 or 660.

[Earendil]

These are your two issues. I would recommend ducting and/or better fluid. I like Motul RBF 600 or 660.

Since you seem so sure, could you explain to me why you think the hawks would produce a mushy brake pedal even after the car is cool? My understanding is that would only happen if they were cooked, but that they would recover as soon as brake temps dropped within their operating range.

[Massive Lee]

Since you seem so sure, could you explain to me why you think the hawks would produce a mushy brake pedal even after the car is cool? My understanding is that would only happen if they were cooked, but that they would recover as soon as brake temps dropped within their operating range.

Brake fluid has gotten hot. Whatever moisture in the fluid has produced vapors. Some of it has condensated back to water when cooling down, some of it is still air.

The cheapest fix is to get much better track pads. Hawk HT10 would be a good start... and ducting.

When you realize the limitations of the stock e30 brakes, then look at improving the brakes themselve.

Some racers can do with stock brakes just because they use way more momentum than most HPDE drivers. But stock e30 brakes still suck... ;-)

[Earendil]

Brake fluid has gotten hot. Whatever moisture in the fluid has produced vapors. Some of it has condensated back to water when cooling down, some of it is still air.

The cheapest fix is to get much better track pads. Hawk HT10 would be a good start... and ducting.

When you realize the limitations of the stock e30 brakes, then look at improving the brakes themselve.

Some racers can do with stock brakes just because they use way more momentum than most HPDE drivers. But stock e30 brakes still suck... ;-)

So I see an argument for better brake cooling there, but not more track oriented brakes. Unless you are telling me that a set of race pads will keep my rotors significantly cooler and thus prevent my brake fluid from ever getting hot enough to boil water? That seems unlikely?

But let's say I add better pads and more cooling. Will this really keep the fluid below 212? Because if you're right that my brake system is pulling/letting in more moisture than most it seems like those two things wouldn't help?

My car is lighter than most E30s, and I never shoot for top speed on the straights. I'm not even half way through the HawkHP+ after 4 track days on them. I'm inclined to think I'm not cooking the pads, especially when braking power never returns.

I'm sorry, I don't mean to be dismissive. I'm just trying to understand completely, partly because I enjoy understanding, and partly because I'd like to be able to diagnose similar issues in the future using a better upstanding of the system :)

[Massive Lee]

The problem on the e30 is twofold. Flexy calipers and tiny rotors. Improving anything costs. Sure, I could have told you to get a BBK with 11.75"x1.25" discs and stiff calipers. But before you get there, perhaps you could improve what you have.

BTW If you drive hard, you will NEVER keep your brake pedal stiff more than half a session. Unless you bleed your brakes every session. ;-)

[Earendil]

The problem on the e30 is twofold. Flexy calipers and tiny rotors. Improving anything costs. Sure, I could have told you to get a BBK with 11.75"x1.25" discs and stiff calipers. But before you get there, perhaps you could improve what you have.

And I would have pointed to the SpecE30 and Pro3 guys that run stock rotors and calipers ;-)
They do however use proper race pads and some (most?) use good ducting. I was going to make that bump when I started out driving my current setup. I suppose I'm just not convinced that I'm overheating my pads.

BTW If you drive hard, you will NEVER keep your brake pedal stiff more than half a session. Unless you bleed your brakes every session. ;-)

Well, it's more than just a lack of stiff pedal, as I don't think in at least one of the session I could locked the wheels if I tried ;)

Since I'm not experiencing brake pad fade, I'll hole off on getting something higher class until after I'm done with the HP+. I'll look into good brake ducting though in hopes that protects my brake fluid. I'm still not sure I understand that though...

[Massive Lee]

And I would have pointed to the SpecE30 and Pro3 guys that run stock rotors and calipers ;-)

And they only do that because of rules. Everyone has the same handicap. The day the rules allow that brakes are free, within a year nobody will run stock brakes... ;-)

[Earendil]

And they only do that because of rules. Everyone has the same handicap. The day the rules allow that brakes are free, within a year nobody will run stock brakes... ;-)

While I do not doubt that many would choose to upgrade, I've also crewed and watched enough races to know their brakes don't function as poorly as mine, and certainly not on a downhill sliding scale over time. I'll try the ducting and leave the BBK for individuals that feel they need them.

[Massive Lee]

Duct to the center of the rotors, so air air is equally spread out, and it will cool the bearings. Don't just direct air at one face. That would be counter-productive.

Cooler rotors means cooler brake pads means not as much heat gets to the brake fluid. Containing heat matters.

[mlytle64]

And they only do that because of rules. Everyone has the same handicap. The day the rules allow that brakes are free, within a year nobody will run stock brakes... ;-)

yes, it is because of the rules, but that does not mean the stock brakes suck. I race an E30 in SCCA. stock brake system with PF01 pads, blank stock rotors, ATE Blue and cooling ducts. I push the brakes WAY harder than any HPDE car. ZERO issues. no fade, no problem hauling car down from 120+ lap after lap after lap. all weekend. same situation in my lap record holding E36 race car. the stock brake systems on E30's and E36's are more than capable of handling a racing environment.

IF

you run pads that can handle the heat and keep the rotors cool. that is the key. as Lee said, containing the heat matters.

in OP's case, your Hawk +'s suck on track. get real pads. and add cooling to the rotors. you will be amazed at the difference.


i am not saying you can't improve on a stock system, just saying that the stock system can run very well with no issues in conditions far harsher than a HPDE driver could ever subject it to.

[Earendil]

yes, it is because of the rules, but that does not mean the stock brakes suck. I race an E30 in SCCA. stock brake system with PF01 pads, blank stock rotors, ATE Blue and cooling ducts. I push the brakes WAY harder than any HPDE car. ZERO issues. no fade, no problem hauling car down from 120+ lap after lap after lap. all weekend. same situation in my lap record holding E36 race car. the stock brake systems on E30's and E36's are more than capable of handling a racing environment.

IF

you run pads that can handle the heat and keep the rotors cool. that is the key.

in OP's case, your Hawk +'s suck on track. get real pads. and add cooling to the rotors. you will be amazed at the difference.

They may suck on track for some (or most) but they work for me likely because I push the brakes way less that you do :)

Given my description, you'd say that my brake fluid is being destroyed, yes?
But I'm also not experiencing brake fade.
So how am I cooking my brake fluid and not fading my hawk "suck" pads?
If I was getting brake fade and then afterwards my fluid was shot, I might understand.

I'll add cooling, but this still baffles me.

[mlytle64]

well, the hawks are clearly NOT working for you. you are cooking them. the compound is not designed to operate at the temps you are getting them to. soft pedal is because they are in a downward spiral. overheated, glazed, you push pedal farther, generate more heat, vaporize any moisture in fluid, pedal goes down more, etc.

you have two very experienced racers, and lee is also a brake expert, telling you the same thing. get better pads and more cooling. keep the HP+'s on the street where they belong.

[Earendil]

well, the hawks are clearly NOT working for you. you are cooking them. the compound is not designed to operate at the temps you are getting them to. soft pedal is because they are in a downward spiral. overheated, glazed, you push pedal farther, generate more heat, vaporize any moisture in fluid, pedal goes down more, etc.

There is a word I haven't seen associated with brake pads before, "Glazed". Perhaps my lack of understanding of what that term implies is where I'm going wrong here.
My assertion that my brake pads weren't failing was based on two things

1. Brakes exhibit a slow progression towards not working over the course of four 20 minute sessions. Slowing down or the start of a new session (reducing or eliminating heat) does not improve the characteristic.
2. By all accounts the HP+ pads when overheated fall off a very scary cliff leaving the driver with little or no stopping power, which I haven't experienced yet.

Perhaps if someone can explain the characteristics of a glazed brake pad to me I could identify that as an issue. For example, can the pad be de-glazed and function again normally after using it on the street? I'm still perplexed by why driving it home, changing the fluid, and driving it back to the track gives me better brakes.

you have two very experienced racers, and lee is also a brake expert, telling you the same thing.

And I mean no disrespect to yours, or anyone else's experience. The last 20 years on the internet has taught me to not blindly believe everything I read, and my engineering brain flat out won't let me. It's probably a handicap so please forgive me :)
Owning an E30 has also taught me not to throw parts at a problem, and r3v has taught me that you can find an opinionated person to tell you just about anything. I only seek to understand exactly what is going on at whatever detailed level people are able or willing to explain.

As I said, ducting will be done as the next project. A set of PF08 were going to be my next pad, so perhaps I'll pick them up early. What about ATE 200? The first guy told me it wasn't good enough and to use Motul, and you said you use it in your race car. From what I've read from the Pro3 guys out here, they tend to use both, with a few people swearing by one or the other.

Get better pads and more cooling. keep the HP+'s on the street where they belong.

Heh. I'd never use HP+ as a regular street pad, and I wouldn't suggest it to anyone either. Head turning noisy when cold, and while acceptable, their cold bite isn't confidence inducing. By going with PF08 I'm probably looking at buying a set of street pads and a second set of rotors just for track days. Oh well.

Thank you everyone for your time :)

[Bimmerman325i]

First, HP+ pads suck. They do. They are autocross pads, and they do not work well at track temps. I've had the exact problem you're having, and the issue is twofold.

First: your pads suck. Get something that doesn't outright give up above 600F, i.e. a real track pad. Lee's suggestion of HT10 is an excellent one, PFC pads are also good.

your fluid is good enough for now. What you mention consistently is that you're not braking hard, abut you're going slow in fast out, and that means you're braking LONG. Braking harder over a shorter distance does not transmit as much heat into the pad and the fluid as a long drawn out braking at less intensity. Heat flow is a function of time.

Ducting is good, and changing pads and fluid will help improve the time before heat gets in, but your technique sounds like you could use more braking intensity over a shorter distance, meaning less time for the same amount of released heat energy to go into your system.

You're an engineer. Mechanical? Heat flow and flux is a differential equation wrt time. While you are converting the same amount of kinetic energy into heat via the brakes regardless of the distance(aka time) spent, you are drastically reducing the amount of time over which that released energy will be able to go into the pad and the fluid and boil things.

My take. I was doing this exactly, braking too long and cooking the brake fluid. Braking harder (much) over less distance solved it right up, changing absolutely nothing. I still use ATE Blue or Typ200 fluid without problems. Still haven't added ducting, still using stock rotors and calipers. Had the same problem on an E30 and my current E36 M3, same solution.