[mihaiilea]

I had a brake failure on track, something went wrong because no matter how hard i pressed the pedale of the car, it didn’t lost speed at all so I hit some barriers.
It is very strange that the car seemed to lost ABS and DSC at that moment. I found that 80.000 cars made for US, and 370.000 cars globaly have a defect at integrated Brake.
https://www.caranddriver.com/news/a4...nction-recall/
https://uk.marketscreener.com/quote/...lems-46251202/
Also 2 weeks before the incident i found some leaks under the car, it was a yellow liquid. I went with the car at the dealership and they have told me the car is ok, they checked it only for 5 minutes.
Anybody has any idea about these problems and what went wrong?
I would appreciate any idea or information.
Thank you in advance for your help.

[lizardx]

From the photos it could be brake fluid. Brake fluid is a bit of acidic and its easy to recognize if it comes into contact with your hands by how it feels.

Brake fluid can also boil on race track, rendering your brakes ineffective.

DSC works in conjunction with ABS unit - so without a functioning ABS, DSC can't operate.


Did you do an error scan? Drop in hydraulic pressure of ABS system should most likely be stored.



My hypothesis would be you had a leak in ABS/braking system; brakes worked until the fluid volume dropped too low, and brakes stopped working.

[mihaiilea]

[QUOTE=lizardx;31127243]I have 10 years of going on track with diffrent cars. Never had any problems.
Also the incident was after staying parked for 40 minutes, go for a warm up lap very slow and start a new lap, at the third braking point i have lost the brakes.
I never do more than 1 hard lap, then cooling for a lap and then i go and stay out at least 30 minutes to be safe.
The car also had the brake cooling air ducts covers removed for better cooling.
The tyres also where at 2.4-5 bar, 52 degress celsius.
I could not understand the situation. The car is curently at the dealer. So i have no acces of reading codes.
I feel that it was more a software error or because of the integrated brake system.
Thank you for your answer!

[CMW33]

Hard to weigh in without knowing more. The G80 M3 doesn't seem to be covered by the brake recall you're pointing to in your post. Describe the brake pedal when the incident occurred. Did any warning/error lights pop up at or just before the shunt?

Without knowing more, overheated brake fluid is a top potential culprit, followed by possible human error.

[mihaiilea]

It was on a normal lap at max 80% after 40 minutes beeing stoped. The car lost 60 km/h in 200 meters from 160 to 100 km/h. That is not a human error.
In 125 meters the car should stop from 200 km/h to 0.
I wish you could never experience that. It is a car problem 200%. The brake booster and integrated brake is the same in a lot of cars.
https://www.carscoops.com/2021/02/20...raking-issues/
It is not the first time for bmw m3!

[myaghi]

After the crash did you check the brake fluid level ? Also when you pressed the brake, did some errors / messages appeared on the dash ?
Did your brake pedal went all the way to the floor when you pressed it?

[mihaiilea]

It was happening so fast... The brake go a little deep from what i have felt. The most interesting thing was that when i touch the brake the car moved under braking ( left right) and my feeling was that front tyre on the driver side was blocked like Abs is not working.
I had a message on the driver front tyre that it has low pressure with 10 seconds prior, but the tyre had 2.5 bar ar 5x degrees, now cold the tyre has 2.0.

The problem is the car has Brake by wire, so you don’t have a connection like in the older car’s. From the pedal to the booster you only have a wire. And the feeling of the pedal is made by a vacumm.
I didn’t look at the liquid after the crash.

[Ximian]

Sounds like ABS "Ice mode" that's written about with some cars. Did you try pumping the brake pedal when the car wouldn't slow down?

Overheated pads would also not let the car slow down quickly enough. Were these the stock brake pads?

As for the 52 degrees Celcius tire temperature, did you get that from the tire pressure monitoring screen? If it's from the TPMS, that's an air temperature rather than tire surface temperature. 52 degrees C isn't particularly warm for track use so that's not an issue.

[mihaiilea]

The tyres are Michelin 4s so i prefer staying around 50-55 degrees when i start a lap to have enough grip at the end of it.
The intresting thing is the car brakes worked perfectly until that moment, the disc and the pads look normal, this was the 3 rd time on a track with the car.
And the brakes where really good for the first corner.
It was like the pedal was disconected from the brakes, i lift a little and than reapply but nothing change. The car was like a torpedo.
The thing is it felt like the car didn’t even try to stop at all.
The dealership is not even looking for a potential problem, i could not understand why is so hard to tell the factory looking after all the data they have! Maybe they can find an answer about what was going on! Thank you for your feedback!

[fl1by]

Could the brakes have been fine and a coolant hose failure or other fluid on the track have simulated "no brakes"?

[mihaiilea]

That is not a possibility, because other 40 cars from the event go past me with no problem and the track was open for a few hours from my event. The track look perfect and clean. Also the grip level was very good in that particular day.