M Coupe brake fluid boiling?

[Z3eattle]

Perplexed by what is going on here. Maybe I just need ducting?

2000 M Coupe
Stock calipers rebuilt 2 years ago with brass bushings (pins re-lubed regularly)
SS lines
Hawk HP+ pads
Stock rotors (Brembo OEM)

Summer 2017 did 2 track days with fresh Motul rbf600; brakes worked great

Spring 2018 did 1 track day on the same rbf600 from previous year (fluid nearly a year old). Brakes worked great until the first corner of my last session (fourth 20 min session) at which point they went soft. Still 'worked' but lots of travel before significant braking, so I called it a day. The weird thing was that there was a latency from my previous session where the brakes were fine, sat for 40 min then experienced the squishy next time out. But I have never boiled fluid before so assumed the hot caliper sitting there waiting for the next session upped the fluid temp enough? I made this assumption given the near year-old fluid.

Bled brakes with fresh fluid and everything worked again. No other track days last year.

Fast forward to first track day of 2019 yesterday: I bled system with 2 qts of fresh rbf600 to avoid last year's problem but it happened again, even with fresh fluid, only this time I got four 20min sessions without a problem. Brakes worked great. They only went soft after I got in the car to go home after it sitting for another 40 minutes. So same latency-to-squishy observation.

Note that this is Pacific Raceways in Kent, WA which has a couple spots of very heavy braking.

The above sums up my track experience with this car so thought I would post here to see what people think. Has anyone experienced a similar situation?

Thank you.

[m3bs]

HP+ is still basically a street pad. Probably need to step up to a dedicated track pad like PFC08. They tend to be a bit hard on rotors, but in my experience they transmit less heat to the calipers.

We’re you able to do a proper cool down lap at the end of your sessions?

[Kondata]

I've been fighting this same issue all of last year. I used 660 fluid with G loc pads and same results as you experienced. After the brakes go soft on the track, they remain that way for almost the entire day. Very inconsistent brake pedal feel and random pedal travel. Makes it nearly impossible to threshold. I've tried bleeding brakes, replacing the booster and master, replacing calipers, tried bleeding ABS...nothing helped.

[m3bs]

My M3 has been a dedicated track car since 1999. The ONLY time I ever boiled fluid was when I decided to try G-Loc R12 pads. Just a data point......

[Kondata]

My M3 has been a dedicated track car since 1999. The ONLY time I ever boiled fluid was when I decided to try G-Loc R12 pads. Just a data point......

Interesting, those are the pads I was running.

[Bobkid]

Couple of things that've worked for me:

One is switch to Castrol SRF. Dry boiling point is similar to RBF600, but wet or used boiling point is much better.
Two is HP+ pads are only good up to the point where you're a solo or intermediate driver. Above that point they overheat quickly and just start smearing. I went from HP+ as a novice, to Carbotech XP12/XP10s as an intermediate, and now run PFC08s in advanced. All this still on stock calipers with dust shields replaced by ducted shields for just a bit extra airflow. Holds up well for hour long sessions and the PFC08 pads have a lot better life than anything else I've run.

[PbFut]

Suspect pads are more your problem than fluid. Chasing brake issues is never fun. Good luck.
My stock caliper set up uses the tried and true ATF super blue now gold thanks to the feds, Carbotech xp20 front xp12 rear. Ducts on front. Stoptech Cryos front and high carbon rear from Summit Racing.
This set performs well everywhere except Auto Club speedway where I probably should have a bit more rotor as I generally come home with too many cracks on the front to risk additional use if it was a good weekend. But no heat fades of any sort.
Auto club has a 160-165mph to 45-50mph turn 2 to turn 3 breaking zone along with 2 other 130-135 zones down to sub 50-60. Thats a lot of heat dynamic in 1 minute and 40 seconds for such a little rotor but if I am careful, it works. The pads and fluid are rock solid. I also have bass bushing in place of the soft silicon OEMs to help with taper. Hope this helps

[Z3eattle]

Lots of great info here. Thank you everyone for the replies.

I will try a dedicated track pad and probably ducting too as it does not seem too expensive. I'll share results to this thread later this season.

[Z3SpdDmn]

Make sure the ears on the pad backing plates are not getting hung up. You'd notice the backing plate bending if this was the case. I don't think this is what you're experiencing, but just check. If that's the case, feel free to grind the ears to create some additional clearance.

Make sure you're heat cycling your pads before you run them hard. Fresh fluid at the beginning of each season is recommended. I run Motul RBF 660. Much cheaper than Castrol SRF and very close. There's also a new LiquiMoly option I'll be running in the One Lap of America this year in a 500hp 1M. Dry boiling point: >320°C (608°F). Wet boiling point: >195°C (383°F). Right between the Motul 600 and 660.
https://www.fcpeuro.com/products/dot...i-moly-lm20156

Also, bedding and heat cycling are two different things. Bedding is done to establish a material transfer layer, while heat cycling is to align the molecules in the pads to better withstand the heat and wear better.
https://www.facebook.com/DriveFaster...15452895217816

[Z3eattle]

Turn of events, but I was rear ended recently and looks like insurance will total the car. I will cut my losses and use the money to put towards...

another coupe of course! I've always liked imola red.

But thanks everyone for their input here. My life is way to busy to turn this around quickly so this ruins my summer track season but I will try to update once I find a working brake solution on a new coupe.

[PbFut]

Well that sucks. Hopefully you will find a better one. Good luck with the search.