Track day soft brake pedal - what to do?

[stoli]

So that last two track days after 5 or 6 hard laps the pedal gets extremely soft. One or two cool down laps and it's right back to normal.

When I was running the oem Brembo pads and Motul 600 I didn't have this issue - it only started after I switched to Carbotech xp10/xp8 and am still on using Motul - it was 'fresh' prior to the last track day. I suspect this is merely coincidence, but figured it worthy of pointing out.

While I didn't bleed the brake before today's session, I did before the last one when I had the same issues.

Bad fluid? Something else? Any suggestions welcome. ;)

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[BlkGT3]

So that last two track days after 5 or 6 hard laps the pedal gets extremely soft. One or two cool down laps and it's right back to normal.

When I was running the oem Brembo pads and Motul 600 I didn't have this issue - it only started after I switched to Carbotech xp10/xp8 and am still on using Motul - it was 'fresh' prior to the last track day. I suspect this is merely coincidence, but figured it worthy of pointing out.

While I didn't bleed the brake before today's session, I did before the last one when I had the same issues.

Bad fluid? Something else? Any suggestions welcome. ;)

Are you running with the Nannies on, if so this can cause excessive heat. IMHO XP10 XP8 are marginal for a car this heavy. I run RBF660 and some will steer you towards SRF but IMHO it is not necessary to spend that amount of $$$. I bleed when I install new pads and have never had issues.

opcorn:

Peter

 

[stoli]

All nannies were off, including Advancetrac. I have Torque RT700 to swap out the Motul before my next outing.

 

[Brent Dalton]

Your fluid is boiling. Did you switch to a stickier tire? Bleed each caliper a little until it comes out clear and you should be good. While I think ATE, Motul, etc... are all great fluids(especially for the price), I've noticed a significant difference between the Castrol SRF and the others. To me, it's worth the extra money. You may be fine with the Motul fluid you have been using though. I flushed mine in Feb before COTA, did a little bleed after that event and it was still clear, and haven't touched them since(probably 7 more days at the track with Hoosiers and 4 or so AutoX's on RE71Rs).

 

[stoli]

Your fluid is boiling. Did you switch to a stickier tire?

That's what I figured but I thought the Motul would have prevented that. I'm still on the same flavor tires (Michelin PSS) but as my skills improve, the braking is much later and harder.

Thanks for the tips.

 

[redtrack]

Try installing brake ducts. You mention you improved your skills, so maybe you are using more the brakes, so ducts are suggested. It makes a hell of a difference.Motul 660 is good as the new Redline.

 

[BlkGT3]

That's what I figured but I thought the Motul would have prevented that. I'm still on the same flavor tires (Michelin PSS) but as my skills improve, the braking is much later and harder.

Thanks for the tips.

Don't think you are boiling your fluid as you stated your brakes came back after a couple of cool down laps. The air caused by boiling does not majicly disappear when the brakes cool down. Still think you need better pads with higher temp threshold.

Peter

 

[Brent Dalton]

Your pedal does come back after a few laps if your fluid boils (obviously if it is not too severe and not as good as fresh fluid that has been bled). If your pads overheat, your pedal does not get soft, it generally feels like your car is not stopping as well, but your pedal is not soft.

 

[stoli]

Your pedal does come back after a few laps if your fluid boils (obviously if it is not too severe and not as good as fresh fluid that has been bled). If your pads overheat, your pedal does not get soft, it generally feels like your car is not stopping as well, but your pedal is not soft.

How about a combination of both then? The pedal was soft/mushy and it wasn't braking as well. I was attributing the decreased brake response to the soft pedal.

 

[JamesinLittleSilver]

Do you have stainless steel brake lines? That was a suggestion our classroom instructor gave. Just a newbie thought.

 

[stoli]

Do you have stainless steel brake lines? That was a suggestion our classroom instructor gave. Just a newbie thought.

Sort of. On all but the left rear. Evidently the threads on the hard line were cross-threaded on the assembly line and we couldn't get the new lines to thread on. I just haven't gotten around to removing them and going back to stock lines on the other 3 corners.

 

[M3Convert]

When the brake system is hot, it will noticeably soften but still engage and you have to adjust your braking to accommodate. This will include a shorter, firmer braking rather than riding the brakes into the turn with increasing intensity.

Is it soft, or just keep going to the floor? [boiled fluid/brown boxers]

Next day, do the brakes shudder? [coated rotors/melted pad compound]
How long to do cool down in the parking area/skid pad/entry drive after each session?

I don't know if they have the size yet, but titanium shims slow heat conduction.

[Did you re-tap the factory thread?]

 

[M3Convert]

Your fluid is boiling. Did you switch to a stickier tire? Bleed each caliper a little until it comes out clear and you should be good. While I think ATE, Motul, etc... are all great fluids(especially for the price), I've noticed a significant difference between the Castrol SRF and the others. To me, it's worth the extra money. You may be fine with the Motul fluid you have been using though. I flushed mine in Feb before COTA, did a little bleed after that event and it was still clear, and haven't touched them since(probably 7 more days at the track with Hoosiers and 4 or so AutoX's on RE71Rs).

I used SRF in my M3 as the MDM mode used to really light up the front rotors - i.e glowing red. After turning TC off, this was less of a problem. In my Mustang, with advanced trac off and the better brakes, I am using Motul 600. To be honest two "shakedown" sessions in the new car, the stock fluid/brakes were just fine while I felt the car out. I switched to Motul as the the fluid needed renewing and as a good precaution

 

[stoli]

When the brake system is hot, it will noticeably soften but still engage and you have to adjust your braking to accommodate. This will include a shorter, firmer braking rather than riding the brakes into the turn with increasing intensity.

Is it soft, or just keep going to the floor? [boiled fluid/brown boxers]

Next day, do the brakes shudder? [coated rotors/melted pad compound]
How long to do cool down in the parking area/skid pad/entry drive after each session?

It was pretty much to the floor in a couple of instances; enough for a serious pucker moment and a run through my head of bailing straight or trying to make the turn, fortunately there was enough left to slow for the turn. ;)

For my cool down I do two full laps (3.5 miles) with minimal braking and then I usually take at least 20 minutes between sessions. The next day, even the drive home, everything is fine.

Did you re-tap the factory thread?

No, for the simple fear the if it gets screwed up I'm either replacing the whole line or, at the least, splicing it.

 

[steveespo]

Stoli
Here is my take on the brake issues you are having.
XP10/8 combo is not sufficient for for either S197 or S550 Mustangs. I have run Carbotechs on my Mustangs for 6 years now and currently run XP24/12 combination, you will not lose pedal to the floor because of these pads and they will be economical in the long run as they will last longer than the 10/8 combo.

Second invest in the Castrol SRF, it lasts longer than the Motul fluids which deteriorate when over heated and lose performance. This could be the problem you experienced in conjunction with the next item.

When bleeding the brakes you should engage the ABS before, then bleed the 4 wheels, then test drive and engage the ABS and then rebleed to check for trapped air. Ford procedure uses their computer system to activate the ABS solenoids in the shop, activating it on the street sort of simulates this. I have personally had good results from this. The extra bleed is a little over the top but I have gotten a bubble or two occasionally.

If you experience this problem after doing the above I would check that left rear brake hose connection that you say was factory stripped, under high temp/high load conditions it could be leaking enough to give you soft pedal then feel normal under daily driving conditions.

Good luck and be careful with the brakes, most important part of a road racing car.
Steve

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