Suspected brake fluid leak after track

[Mortis]

Hi everyone,

I'm back on the forum after a hiatus of several years, with a brand new to me 2017 M4 competition (I used to be on here with my 2015 M4). I took it to the track for the first time this weekend (Summit Point in W. VA) and had a blast. Learning from past mistakes and from all the advice on this forum I installed Pagid RS29 pads and dedicated track wheels (Nitto NT01s, staggered 275/305 setup).

When swapping brake pads I had slight leakage of brake fluid from the reservoir (which I understand sometimes happens when moving the pistons) - also had the cap unscrewed. It was very little and obvious to me what happened so I paid it no mind.

The car behaved amazingly on track, I rejoiced in the new brakes and tires, and was able to push the car harder than previous times. On my very last session I had brake fade, which I chalked up to either stomping on the brakes excessively or boiling my stock brake fluid. I plan to do a flush with castrol SRF this week just in case.

The morning after returning home I took the car out for errands and later that day saw a much larger leak of what I believe is brake fluid under the car, coming from somewhere in the middle of the undercarriage, just behind the front wheels. It has the same consistency and color as the brake fluid so I'm wondering if I sprung a leak somewhere.

Has anyone experienced this or have some advice? I checked the forum and while there have been plenty of posts on brake fluid reservoir leakages while swapping pads, I haven't seen anything matching this case...

Thanks in advance, and greetings to all the old friends on the forum!

[Suds]

I have never seen that on 2 M4 that I have tracked. Is it possibly brake fluid that leaked from over filling the reservoir?

I have always flushed the stock brake fluid with SRF before tracking a car.

[jfritz27]

If using a pressure bleeder, I'd imagine that if a leak is there somewhere, you'll provoke it when the system is pressurized. Keep your eyes peeled

[icegrill]

Originally Posted by Suds

I have never seen that on 2 M4 that I have tracked. Is it possibly brake fluid that leaked from over filling the reservoir?

I have always flushed the stock brake fluid with SRF before tracking a car.

I had a similar leak in my 135 and it was from the level being too high in the brake fluid reservoir.

[NYG]

Did the level in the master fluid reservoir drop?

Did you over tighten the bleeder and strip it maybe? (Real easy to do)

The hard line is visible in the back/top of the wheel well so you should be able to trace it. It's not likely that you're leaking before that so leave that for last.

[Mortis]

Thanks everyone. Turns out the fluid I found the day after my return from track was the original fluid from when I swapped brake pads. In my haste to get out the door I forgot to clean it and thought it had evaporated, which of course it had not. Now I feel like an idiot...

[jfritz27]

Originally Posted by Mortis

Thanks everyone. Turns out the fluid I found the day after my return from track was the original fluid from when I swapped brake pads. In my haste to get out the door I forgot to clean it and thought it had evaporated, which of course it had not. Now I feel like an idiot...

Be thankful for the easy win.

[Spun Crankhub]

Originally Posted by Mortis

On my very last session I had brake fade, which I chalked up to either stomping on the brakes excessively or boiling my stock brake fluid. I plan to do a flush with castrol SRF this week just in case.

In my experience brake fade usually occurs by using too much brake, ie riding the brakes, and not from hard short bouts of braking.

Glad you remedied this.

[Mortis]

Originally Posted by Spun Crankhub

In my experience brake fade usually occurs by using too much brake, ie riding the brakes, and not from hard short bouts of braking.

Glad you remedied this.

Originally Posted by Spun Crankhub

In my experience brake fade usually occurs by using too much brake, ie riding the brakes, and not from hard short bouts of braking.

Glad you remedied this.

Thanks. I suspect I was on the brakes too long going into turn 1 on summit point after the long straight. I was decelerating from 150 mph to about 45 mph for what is a very tight turn. I've heard this corner is tough on heavy cars like the m4. Next time probably need to back off on the speed a bit...

[NYG]

Originally Posted by Spun Crankhub

In my experience brake fade usually occurs by using too much brake, ie riding the brakes, and not from hard short bouts of braking.

Glad you remedied this.

Brake fade occurs from thermal loads. You're dissipating the same amount of kinetic energy into heat for both cases (with minor losses spread between other components/aero/etc). With more experience you can take corners faster and brake less - which helps but the lack of airflow to the brakes is a legitimate problem with the platform. The grippier the tire gets, the more obvious this will become.

Overtime, I'm starting to realize that my forward rake was probably a bad idea on the M4.

[r4dr]

Originally Posted by NYG

Brake fade occurs from thermal loads. You're dissipating the same amount of kinetic energy into heat for both cases (with minor losses spread between other components/aero/etc). With more experience you can take corners faster and brake less - which helps but the lack of airflow to the brakes is a legitimate problem with the platform. The grippier the tire gets, the more obvious this will become.

Overtime, I'm starting to realize that my forward rake was probably a bad idea on the M4.

I don't think that's correct.

Braking less means converting less kinetic energy into thermal energy because, well, you're slowing the car down less. Most people who aren't pro race drivers brake too much.

Also, braking harder for shorter time might convert the same amount of KE to thermal energy but if you do this over less time you have more time to shed that heat and manage it.

[NYG]

Originally Posted by r4dr

I don't think that's correct.

Braking less means converting less kinetic energy into thermal energy because, well, you're slowing the car down less. Most people who aren't pro race drivers brake too much.

Also, braking harder for shorter time might convert the same amount of KE to thermal energy but if you do this over less time you have more time to shed that heat and manage it.

If in both instances the initial velocity and the final velocity are the same then the work done from braking is equal - it's the same change in kinetic energy. The heat added to the system will not vary much because the impact of drag and other forces slowing you down don't contribute enough in such small increments. We're not talking about going from 150mph to 70mph between 1000ft and 5 miles - we're talking about 1000ft to maybe 1200ft.

It's true but it's not because they're braking earlier and lighter. They're braking later and harder, the difference is that they enter corners faster so there's less work being done by the brakes resulting in less heat.

[r4dr]

I think you're talking about rate of braking and I'm talking about the speed delta from braking...