Do I need to bleed the brakes after every track day?

[dparm]

Car: 2011 M3 sedan with ZCP
Tires: Yokohama AD08R
Front brakes: StopTech ST40, slotted rotors, SP pads
Rear brakes: OEM rotors, SP pads
Fluid: SRF

After my first full track day on the StopTech kit, I noticed that there's a little bit more pedal travel now when driving around town. Did a bit of air really get into the system after just one track day, and if so, do I need to rebleed them with fresh SRF before the next track event?

I understand from a performance perspective that having the freshest fluid possible is a good thing, but I'm still surprised that after just one full track day there is already a different feel to the pedal.

Also, is there anything special to know about bleeding the ST40 caliper?

[nholmes]

Did you boil the fluid?
How much material did you shed from the pads?

I always bleed after every event and flush once a year, but that's me. It's the only thing stopping the car at 130+MPH so why risk it?

[jphughan]

I've never bled with SRF, just flush annually, and that's not an uncommon practice with SRF. A bit of pedal feel change at the end of a track day is normal and totally fine. It won't keep getting worse.

[1MOREMOD]

No, even with lesser fluid

[Groundpilot]

No need to bleed with SRF flluid. I flush it once a year and never have problems.
However, if you just installed yout BBK, installation of new calipers and brake lines introduces a lot of air in the system.
I remember, when i did that, i had to flush many many times untill i got all the air out.
So make sure your brake system is free of air

[dparm]

Originally Posted by nholmes

Did you boil the fluid?
How much material did you shed from the pads?

I always bleed after every event and flush once a year, but that's me. It's the only thing stopping the car at 130+MPH so why risk it?

Nope, brakes were consistent all day long. We had 5 30-minute sessions with an hour of downtime between. Ambient temp was about 70 in the morning and 80 in the afternoon.

Unsure how much pad wear there was, I haven't had time to measure. I live in downtown Chicago and it's tough to work on the car here.

I will take the first session cautiously this Friday evening. I have an extra bottle on hand in case I need to bleed the lines at the track.

[M3 Number 86]

How much more pedal travel do you have? Might be because pad thickness or type of pad. I've noticed this even though internetz swear it's not a reason.

[dparm]

Originally Posted by M3 Number 86

How much more pedal travel do you have? Might be because pad thickness or type of pad. I've noticed this even though internetz swear it's not a reason.

Hard to say. It's noticeable, but not huge. It's not like there's no braking until it's halfway to the floor. I just have to push the pedal a bit more now.

I too assumed "less pad material, therefore it has to travel further". Everyone I talked to has said that's baloney and the piston location adjusts with pad wear. Dave Zeckhausen said the change in pedal feel means there are air bubbles.

I should probably pull the pads and inspect them. One theory is that they glazed or something, which might feel like less stopping power.

[M3 Number 86]

Originally Posted by dparm

Hard to say. It's noticeable, but not huge. It's not like there's no braking until it's halfway to the floor. I just have to push the pedal a bit more now.

I too assumed "less pad material, therefore it has to travel further". Everyone I talked to has said that's baloney and the piston location adjusts with pad wear. Dave Zeckhausen said the change in pedal feel means there are air bubbles.

I should probably pull the pads and inspect them. One theory is that they glazed or something, which might feel like less stopping power.

Yeah I never understood the self correcting for lack of a better term. How does that work technically?

If you have full pads at full fluid the piston doesn't have to press as much. As the pad wears down the piston doesn't retract as much assuming the edge of the pad is always the same distance to the rotor as it wears down?
(I butchered the choice of words but you get the picture).

Can someone explain?

Because when I swap back in new full track pads it feels instantly better - that's why I never understood this.

And when I put in stock pads it feels different too (initial bite because material?)

[dparm]

Originally Posted by M3 Number 86

Yeah I never understood the self correcting for lack of a better term. How does that work technically?

If you have full pads at full fluid the piston doesn't have to press as much. As the pad wears down the piston doesn't retract as much assuming the edge of the pad is always the same distance to the rotor as it wears down?
(I butchered the choice of words but you get the picture).

Can someone explain?

Because when I swap back in new full track pads it feels instantly better - that's why I never understood this.

And when I put in stock pads it feels different too (initial bite because material?)

Dave Zeckhausen's answer to me was:


The pistons don't travel any further in and out as the pads wear. Instead, the level of fluid in your reservoir drops over time and the pistons' new "home base" is slightly further extended than it was when the pads were new. But the piston location adjusts with pad wear, so there's no increase in piston travel. The longer pedal is due to air bubbles being compressed.

[jphughan]

Originally Posted by M3 Number 86

Yeah I never understood the self correcting for lack of a better term. How does that work technically?

If you have full pads at full fluid the piston doesn't have to press as much. As the pad wears down the piston doesn't retract as much assuming the edge of the pad is always the same distance to the rotor as it wears down?
(I butchered the choice of words but you get the picture).

Can someone explain?

Because when I swap back in new full track pads it feels instantly better - that's why I never understood this.

And when I put in stock pads it feels different too (initial bite because material?)

The pistons always retract the same amount from the pad backing plates. As the pad gets thinner, that means the pistons even when retracted are farther extended than they were when the pads were new. The extra space created by the pistons extending farther out as the pads wear down is taken up by the brake fluid in the reservoir dropping from the reservoir above the master cylinder down into the force path from the cylinder to the pistons. That's why they tell you never to top off your brake fluid while you have worn pads, because if you then swap new pads in, pushing the pistons back, you can have an overfilled brake fluid reservoir.

The pedal travel and initial bite difference between different has to do with differences in the compounds. I don't know the technical details around that.

[M3 Number 86]

Originally Posted by jphughan

The pistons always retract the same amount from the pad backing plates. As the pad gets thinner, that means the pistons even when retracted are farther extended than they were when the pads were new. The extra space created by the pistons extending farther out as the pads wear down is taken up by the brake fluid in the reservoir dropping from the reservoir above the master cylinder down into the force path from the cylinder to the pistons. That's why they tell you never to top off your brake fluid while you have worn pads, because if you then swap new pads in, pushing the pistons back, you can have an overfilled brake fluid reservoir.


The pedal travel and initial bite difference between different has to do with differences in the compounds. I don't know the technical details around that.

-makes sense
-regarding compounds i think it's just a "grabby" vs "modulateabler" compound lol

[g2]

If this was your first DE you were likely on the brakes longer than you should have been. Pretty common for folks new to DE's. You might have boiled the fluid or over heated the pads. Do you have another set of pads to swap in and check?

[dparm]

Originally Posted by g2

If this was your first DE you were likely on the brakes longer than you should have been. Pretty common for folks new to DE's. You might have boiled the fluid or over heated the pads. Do you have another set of pads to swap in and check?

Wasn't my first DE. It was the first full day on those brakes and the new AD08R tires. I did not have any change in brake feel over the course of the day, so I don't think the pads or fluid were overworked.

[silvergray545]

Originally Posted by M3 Number 86

How much more pedal travel do you have? Might be because pad thickness or type of pad. I've noticed this even though internetz swear it's not a reason.

I thought I was going crazy. I feel like I have way more pedal travel with the PFCs. I was going to bleed the brakes tonight thinking that might be the issue.

[nholmes]

Originally Posted by dparm

Dave Zeckhausen's answer to me was:


The pistons don't travel any further in and out as the pads wear. Instead, the level of fluid in your reservoir drops over time and the pistons' new "home base" is slightly further extended than it was when the pads were new. But the piston location adjusts with pad wear, so there's no increase in piston travel. The longer pedal is due to air bubbles being compressed.

This is why I had asked you if you boiled the brakes. Also, SRF is still hygroscopic and will leach moisture out of the air, which will contribute to boiling IIRC.

[dparm]

Originally Posted by nholmes

This is why I had asked you if you boiled the brakes. Also, SRF is still hygroscopic and will leach moisture out of the air, which will contribute to boiling IIRC.

Yep, understood, but this fluid is barely two months old and has only seen one full track day. The car isn't even a DD, it sits in the garage most days.

[swartzentruber]

Give a few more days. I've noticed sometimes that immediately after a track weekend, the pedal might feel a little softer, but goes away after a few days. If after a week it still feels a little soft, then as others said, probably with a new BBK, might need another bleed, just because it's a new system. But no, if you are running SRF, you should NOT need a bleed after a single day, and in fact, shouldn't need to bleed all year.

I just had Fall Line rebuild my Stoptech fronts, and they mentioned it would likely be a good idea to do one more hot bleed after putting a few miles one them, I'm thinking due to the air introduced by the reinstall.

[will.c]

I personally think SRF is waste of money. I've used them for past year or so, but I had to bleed them after every event, just as I had to with RBF - no tangible difference in performance nor longevity, yet double the price. I'm going back to RBF.

If you get your brakes hot enough, you need to bleed before every event. Everyday within an event may not be necessary, but YMMV.

[jphughan]

Originally Posted by will.c

I personally think SRF is waste of money. I've used them for past year or so, but I had to bleed them after every event, just as I had to with RBF - no tangible difference in performance nor longevity, yet double the price. I'm going back to RBF.

If you get your brakes hot enough, you need to bleed before every event. Everyday within an event may not be necessary, but YMMV.

Weird, you're definitely in the minority there on bleeding after every event. Most people don't even do that with Motul. Did you ever try just going to the next event WITHOUT having bled after your last one just to see how the SRF would behave?

[MFKN3]

I always bleed them before going to track. Even if its just an egg cup each. The front lines always bleed out a bit dirty. I use 600 race fluid

[jphughan]

Originally Posted by MFKN3

I always bleed them before going to track. Even if its just an egg cup each. The front lines always bleed out a bit dirty. I use 600 race fluid

Seeing dirty fluid doesn't justify a bleed. Oil would drain a bit dirty way before it should legitimately be changed too.