Causes of brake fade on a track day

[Ridowh 8]

Hello all,

I searched for this but couldn’t find anything specific. 

(The background):

I tracked my car at Goodwood last October/November. At the time my car was an auto GTS (Australian import) with an HKS Supercharger and Cobra Res Catback done by Fensport, plus some lovely ECUTek magic done by Adrian there. 

The rest of the car was stock (Australian) standard at the time (I’ve fitted Tein Flex As and EDFC Active Pro since, with GPS, and adjustable front and rear links etc.). Our next track day is booked for July. 

The car was running brilliantly and I was pushing more and more with each lap and the car was totally solid.  The only problem I had was a big fade under very heavy braking at the end of the long straight there. Probably coming down from close to 140mph to about 40mph. The brake pedal went straight to the floor and, even though the car did slow, it wasn’t sufficient to make the corner and I tried to demolish the plastic guide arrows along the left hand side of the track. Fortunately they were the rebound type so they just left a load of white marks all over the front wing and under the left hand skirt. No biggie. 

The friend I was doing the day with reckoned that just changing the pads to something more heavy duty would prevent this happening again. I have since purchased Goodridge braided lines, a master cylinder brace, DoT 5.1 fluid, and HPS Hawk pads front and rear. The pads have all been fitted and run in. The feel is massively better even though it’s only been for road use so far. I haven’t gone as far as to fit the lines, brace or change the fluid. I am keen to only make one change at a time, and since the last track day the car now has the Teins and EDFC units fitted, however I simply can’t afford to run a track day, even a half day one, every time I want to test a change. 

 

(The question) (*sigh* finally, I hear):

In your experience, to what extent do you think that fitting just the pads will have relieved the situation? 

 

Many thanks for your time,

 

Richard

[Kaltorak 111]

That's one hell of a braking zone. I can't think of another track that would be that brutal on brakes. Ignore that, missed the supercharger part in the description.

The pedal going to the floor suggests that the brake fluid boiled, fluid doesn't compress, but the "air" after it boils does resulting in a very long pedal. 

Did it remain long /spongy afterwards, if so that's probably the cause. 

If not, you probably overheated the pad material which would have resulted in it having a huge drop in friction so pushing the pedal would result in far less braking force. 

New pads will have a large impact, the stock ones just aren't up to heavy track abuse, particularly in a super/turbo car.  I think of those that track the car and have gone the FI route they all have a BBK. The dot 5.1 would help prevent the fluid boiling, depends which of the symptoms you had. 

Unrelated, but if you don't have an oil cooler you may want to keep an eye on oil pressure /temp when on track if you don't already. 

[Ridowh 8]

Thank you Kaltorak,

I agree with you, my first impression was that of a fluid boiling situation, causing bubbles in the lines, however within 30 seconds of it occurring they felt ok again. I pulled off the track at the pit exit and stopped to talk to an official (to see if I had left a trail of debris behind me on the track) and the brakes were cooking big time so he sent me off to drive out to the main road and back to cool then down. 
The way the pedal felt reminded me of the way a brake pedal felt many years ago (back in the Mini modding days of my late 20s and early 30s) and I was in the process of changing, and bleeding to a brake fluid. 
I haven’t experienced brake fade due to heat before though, so I wanted to ask. 
 

As for the speed, I had been totally flat out down the longest straight there before braking. It was an estimate. The car still had some more to give, just not enough straight left.  I totally love the track at Goodwood, it’s technical enough to be a challenge, and difficult enough to really teach yourself a lot. 

[Church 209]

Fitting just the track oriented pads will ensure good brake friction even on high temps seen on track (cons being that track pads are are less fit for dailydriving use, where they never get upto operating temps, wear off bedded in layer on rotors, after which they squeal and wear at extra rate. Hence reason, many use two pad sets and switch between/after trackday).

If you had brake fade, it was imho more because boiled fluid then pads. I'd just get some of much higher boiling temps one, eg. PMU G-Four 335, Endless RF650, Castrol SRF, Brembo HTC 64T. Replacing it costs less then pads and is simpler, and has no drawbacks then maybe need to change it quicker (due usually high boiling temp brake fluids being more hygroscopic, so they often absorb moisture quicker and may have their properties worsen by time)

But in general your problem was overall insufficient brake heat capacity for said track/supercharger/good tires combo. Track has long straight ending with very very heavy braking, supercharger accelerates car quicker thus from higher speed car needs to be braked down to speed it can take turn (and to be converted to heat with brakes kinetic energy is square(!) of the speed), grippier tires - one can turn quicker, exit from corners quicker, get higher speed .. and again more heat for brakes.
Ideal way for extra heat capacity of brakes would be fitting BBK. But it costs a lot, and may need some other spendings, eg. if currently used wheels don't clear it. You also can increase brake heat capacity with adding cooling solution, eg. brake cooling ducts. Or maybe even something like this . But cost & overall complexity of electric cooling .. i'd get "classic BBK" probably first.

[will300 812]

Your issue will be a combination of the brake fluid boiling and the pads overheating, as already mentioned by @Kaltorak

With regards to your mod plans, braided lines and master cyclinder brace won't make much difference as they affect pedal feel, not braking ability. From my own experience a strut brace with built in MCB is better for feel than just a MCB, having run both. 

Also assuming your on stock calipers, you probably want a better pad than Hawk HPS for track use as the Hawk pads are still a street biased pad. 

Which fluid have you gone for? In the past I've used ATE Type 200 and didn't really get on with it as I kept over heating it. I've since replaced it with Millers Racing Brake Fluid 300+ and not had any issues. 

Final point, when you bleed/replace the brake fluid, you also need to bleed the master cyclinder if you don't do this it can leave air in the system. 

[Rich196 103]

Pedal straight to the floor I would say means boiled fluid. I always use RBF600 on anything I track its just not worth the risk in my opinion. Its probably one of the bigger stops in the UK so fluid and better pads will tided you over. 

With the charger my experience was DS2500 didn't cut it and they faded after a lap or two. I then when to a carbotec XP10 and they didn't fade except on the ring GP, but that used to have the biggest brake in F1. I also added brake cooling ducts off a GT3. I think they are about £30.

2020-10-12_09-21-03 by Richard Beale, on Flickr

[MovesWithClouds 5]

Someone told me the thickness of the pads is part of the protection against boiling brake fluid, which is the real danger(brake fading is merely annoying): the risk is higher when the pads are worn.

[surrey86 352]

Fluid was your issue there, probably not helped by OEM pads. 

For track work fluid is the first thing you change. To be honest what happened to you was inevitable on a forced induction car on track with no braking upgrades. The standard brakes are barely adequate on an unmodified car on track, I wouldn't even do a day on standard fluid with that.

[Booboo 11]

I have Hawk HPS pads and used with DBA T3 4000 discs are sufficient for a few hard laps at Anglesey but I needed to back off due to fade if I pushed them much beyond that. Obviously Anglsesey does not have any long straights to speak of so they don't get much chance to cool without backing off. They are a great combo for road use but I suggest you look elsewhere for a more track orientated pad