Big Brakes On Track

[Keethos 842]

As some of you may know I've been running the K-Sport brakes on the front of my car for a short while now, after initial issues of the pads partially seizing and subsequently not wearing properly (outside pads wore out very quickly while the insides still had plenty of meat left, plus it managed to round the top outer edge of the disc), I've now had a new set fitted (well part worn, I know I know, cheap skate here but they were given to me) after the previous ones were literally hammered out, cleaned and new discs fitted.  I've now had my first proper track day in them at Cadwell part the other week and it really does stop, it doesn't have mega initial bite like the Stoptech pads I had on the stock calipers but they are very progressive, you continue to apply more pressure and they begin to stop even more.

 

Here's my query, after lunch and numerous laps around Cadwell, when I went back on track I felt that the pedal felt very soft, like it didn't want to do anything until you push the pedal a good 60-70% the way down, then it'll really start to slow you down (compared to roughly 40% the way down when it'll start to seriously slow you down during the morning), so it lost it's progression and required me to put my foot further down but it didn't lose it's braking power.  This because even more obvious as I started to struggle to toe heal because as my toes were having to travel further down, I was struggling to reach the gas pedal or modulate it properly.  Anyone know if this is normal?  (After the car had properly cooled down it returned to normal)

 

Another thing that I am noticing is that when I apply a little bit of brake (even when stationary), I feel the pressure behind the pedal initially but then suddenly the pressure suddenly drops.  Also when stationary, when I apply the brakes, I can push the pedals down about roughly 60% of the way down with a bit of resistance, but then if I lift off and apply the brakes again I get a lot more resistance and only travel roughly 50% of the way down.  Is this right?  Is there air in the system maybe?  I'm uncertain about how things should be since I've been driving around with them partially seized etc for so long that I don't even know what's normal and what's not any more.  Any info is much appreciated thanks.

[S18 RSG 429]

I'm no expert, but if I were to have that problem I would assume brake fluid. What DOT rating fluid are you running? If the DOT rating is a little low (i.e not DOT 5 or DOT 5.1) then you might find you're exceeding the "effective operating temperatures" (can't think of a better term), and therefore, in effect, thinning out the brake fluid (much like what happens when oil gets too hot).

Aside from that, perhaps a set of braided lines may be a worthwhile upgrade, as standard brake lines would be likely to expand as the fluid heats up, and obviously with a larger diameter pipe, you have less pressure, and therefore need more brake input for the same result.

Hopefully someone else has some first hand experience, as all I'm saying is based on fluid theory more than experience.

[Keethos 842]

I've recently had DOT 4 fluid put in by Mike@Tuning Development (I think) which he assured was great for track use and I think the brake kit came with braided lines too.

[Rich196 103]

@Keethos Sounds to me as though you either have air in the brake system, or you have boiled the brake fluid, can you tell me what brand of fluid you are using?

Have you do much track driving in the past?

Are you doing a cool down lap when you come off track?

How many laps are you doing on a track session?

What setting do you have the traction control set in?

What is the rear brake setup?

[Andrew Smith 156]

I spent the day at Cadwell yesterday and with Mikes brake kit (yellow pads, uprated lines and high boiling point fluid) I didnt lose much braking, in to Mansfield sometimes they faded but they soon recovered, the tyres gave in before the brakes. Never had a brake system that doesnt benefit from a pump

[Keethos 842]

No idea what brand of the fluid has been put in (can you answer that @Mike@TD.co.uk?), I do a fair bit of track driving but first time after a fresh set of discs and pads with the K-Sports, I usually do a cool down lap after about 5 - 8 laps roughly I think.  Traction control is usually in Sport mode (if I can remember to turn it on, still haven't built up enough courage to turn everything off yet) and the rears are still stock with Stoptech pads I think.  Again no loss in braking power, just requires more brake pedal travel and less initial response.

[Rich196 103]

Sounds to me like boiled or old fluid in the system, perhaps cycling the ABS pump has moved air or old fluid. I would try bleeding the brakes first. use a clear pipe on the bleed nipple and you will see air bubbles if that is the issues. Quick and cheap to find out!

If you are over braking, due to lack of track knowledge, and the traction control is using the brakes a lot it will lead to quickly to over heated fluids. Big multi pot brakes can make this a bigger issue as they contain more fluid, and can hold heat better.

[Keethos 842]

I believe the brake fluid is ATE DOT 4 fluid.  As for over braking, I've been to Cadwell Park a few times now (including tuition time there as well) so I'd like to think that I'm familiar with the track.  There are a couple of corners that required some big braking but most corners only require a little dab and the traction control would only really kick in severely when going over the mountain (even though you're pretty much straight, due to the hump, the car lifts a bit and the traction control goes mental cos it thinks you're losing traction). 

[Mike@TD.co.uk 467]

ATE Typ200 fluid was installed Keith. The full system flushed prior.

 

You mentioned a weep from a front caliper before bringing it in to us, have you ensured that isn't happening again? Also what pads are you using? (apologies if i've missed that info above) Same for the rears too...

 

We run the KSport kits front and rear on the Celica and the 86 and haven't had anything like your feedback Keith. Especially in the 86 as the ABS I feel is far to quick to kick in on these cars.

[Rich196 103]

8 minutes ago, Keethos said:

I believe the brake fluid is ATE DOT 4 fluid.  As for over braking, I've been to Cadwell Park a few times now (including tuition time there as well) so I'd like to think that I'm familiar with the track.  There are a couple of corners that required some big braking but most corners only require a little dab and the traction control would only really kick in severely when going over the mountain (even though you're pretty much straight, due to the hump, the car lifts a bit and the traction control goes mental cos it thinks you're losing traction). 

 

Sounds like air in the system to me then! Dont think from the sounds of its anything your doing, and I certain wouldn't expect this behaviour.

If what @Mike@TD.co.uk is saying is true, as leaky calliper would cause the issues as it will cause a pressure loss. Have you lost any brake fluid?

 

 

 

 

[Keethos 842]

Hi Mike, no the brakes aren't weeping any more and there the fluid is still at max (it might even be a lil over), the pads are K Sport ones again I think and the rear are Stoptech.

Is there a way to test if the pistons are travelling smoothly?  

[Ade 517]

Sorry if I missed it but what pad compound are you using?

[Keethos 842]

Hi Ade,

Are you asking me what make are the pads or the actual material composition?  Because if it's the latter I have no idea!

[Ade 517]

14 minutes ago, Keethos said:

Hi Ade,

Are you asking me what make are the pads or the actual material composition?  Because if it's the latter I have no idea!

Sorry jsut the pads themselves. Are they K sport or Ferodo or something? 

The reason I ask is you can lose initial bite with over heated pads.

[Keethos 842]

Fronts are K Sport BBK I believe and the rears are stock size Stoptech

[Ade 517]

11 minutes ago, Keethos said:

Fronts are K Sport BBK I believe and the rears are stock size Stoptech

What kind of pads are those k sport pads? If they are a street compound then it might be pad fade.

[Keethos 842]

I honestly have no idea, the first set came with the kit and the ones I've put in now were given to me so probably again came with them. But doesn't brake fade equal less stopping power? As the brakes only loss progression and required more pedal travel but still stopped well.

[MikeB 79]

Keith, I run Goodridge hoses and ferodo 2500 pads with higher boiling point fluid with no issues. Castrol React SRF racing brake fluid, it's expensive but worth it.

[Lauren 2259]

In all honesty, what you report is perfectly normal for what happens when you get brake fade. The drop in pedal when you are stationary is due to the servo. Happens on every car. 

[KevinA 695]

Just do what Lauren does........don't brake 

[Keethos 842]

Good plan Kev but I don't have the skills or the cojones. It's just strange as I don't remember experiencing the pressure drop on the pedal but then again the calipers were seizing/sticking for a long while. Thanks all for your inputs, I'm guna try some other pads maybe before my next track day but might stick with them for the next TSS since I shouldn't experience any fade on short sprints I hope.

[Lauren 2259]

Maybe you need a better choice of pads? 

[Keethos 842]

That's the idea, stick some ferodo pads on.

[KevinA 695]

I had DS2500 on for a while and didn't like them, no bite when cold / cool. Found both Stoptech and Hawk to be better, but guess you are limitrd to the disc set up. I have used Ksport a lot in the past and they were very good.

[Ade 517]

I really liked project mu hc800+ for rosd and track. Ill be trying them on my AP racing kit after I finish the streetmasters.