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View Full Version : Brake advice - cooking brakes (not the usual question!)


boro92
12-18-2015, 10:54 PM
Hi guys,

Hoping someone can chime in and assist here.
I'm facing an issue with brakes (duh - per post title!). They work fine on the track. Pedal is firm, pads work out etc. I usually give the car 2 warm up laps and 2 cool down laps at the start/end of my run. When I complete my cool down lap, my pedal is still there. Now, I pit for maybe 20 minutes or so and let everything cool off. Jump in my car again and touch the brakes - pedal goes to the floor.

What's happening here is that my fluid is cooking when the car is in the paddock without any airflow going to the caliper. All the fluid in there is cooking. Give the brakes a few pumps to circulate the fluid, and the pedal firms up...but of course, by now, the pedal is no longer 100% and needs to be bled after the track day.

Should I simply accept this as the norm (read: required bleed before/after each event), or have u guys found a way around this?

I find it doesn't matter what I do - stock brakes. Use ducting. Stoptech 355's. Same problem after pitting. Sometimes it's better, and it takes a couple sessions before the fluid in the brakes just heat soak from sitting in the pits. But it always does -- and only ever does this in the pits!!! What gives? Should I give it more cool down laps? Is there a cool down lap technique? I tried not touching the brakes--i find this doesn't help, 'cause the fluid just stays in the caliper. So instead, I go at a slow and steady pace and only use the brakes sparingly when needed. No dice either way (although it is better when I dab the brakes during cool down). Help?

Slowpoke
12-18-2015, 11:37 PM
What car, what weight and horsepower, what pads, what fluid, have you trimmed your rotor splash shields to allow more heat dissipation (protecting only the ball joint and tie rod end), what diameter of ducting and does it come straight from the front bumper?

boro92
12-19-2015, 09:56 AM
Good questions!!

This problem occured on a boss302 with brake ducting to the ceter of the rotor with 3 inch hoses and ti pad shims. Ran motul 600 fluid but stock pads (yes, i know). Stock power and weight (3650)

Current car is s4 with stoptech 355 st60s. No splash shields, castrol srf. Pfc1038 pads. No ducting. I plan on adding some porsche brake scoops, however. Stock power aand weight (3890)

wings2k
12-19-2015, 11:41 AM
what track? This is very odd.

h-bomb
12-19-2015, 11:57 AM
When bleeding do you notice air bubbles in one caliper moreso than the rest? Perhaps it's one sticky caliper that's causing the issue?

I would expect an S4 with quality pads and fluid to be able to handle the abuse in stride.

Slowpoke
12-19-2015, 12:31 PM
1038 is an older compound and I don't have personal experience with it. But the one time I had an experience just like you describe was making a PFC 97 do far too much work for it's coefficient of friction. Pad didn't completely go away while on track but braking distances got really long.

You can confirm it with Brembo caliper temperature witness stickers.

Both cars are high horsepower, high weight. Is this happening on tight tracks like DDT? My guess is you're on the brakes too long. Need to have less time with pads engaged.

Other possibility was that pedal might not have been releasing completely because master cylinder engagement too aggressive. Once the fluid heats and expands, there would be constant drag. Might need more free play at the top of the brake pedal stroke.

boro92
12-19-2015, 02:21 PM
Good point on the MC pressure. Hadn't considered that.
What's the usual solution there? Run slightly less fluid (like 20ml less than full??). The issue primarily is on DDT and Shannonville. not really a problem at mosport gp. Shannonville I'm doing 2:03.1 on street tires. The worst part for the brakes is turn 13.

FWIW when I had this problem, the pad was dragging slightly on 1 caliper. The abutments were very tight on the pad and it wasn't releasing fully every so slightly - so that could be it.

But it sounds like from everyones experience, this should never be a problem? With some cool down laps and pitting, the fluid in the calipers do not heat soak? In general, I find I need to pump the brake pedal after the car has sat in the pits for a while. Otherwise, the pedal travel is very long.

10gt61
12-19-2015, 04:52 PM
Good questions!!

This problem occured on a boss302 with brake ducting to the ceter of the rotor with 3 inch hoses and ti pad shims. Ran motul 600 fluid but stock pads (yes, i know). Stock power and weight (3650)



I had a similar set-up on my Mustang GT; Ford Racing brake cooling ducts to the rotor, hi-temp brake fluid, no shield, good rotors and track pads (have used Carbotech and Hawk). I didn't have this issue, although the brakes did get soft after two long days at WGI a couple years ago.

An obvious question, but did you turn off your Traction Control and Electronic Stability System? With those on the car will be braking when you don't know it. I learned this the hard way a few years back, losing the rear brakes in one track day!

boro92
12-19-2015, 05:47 PM
Hi Kelly, yup everything is full off of course :) good to know you had luck with the Mustang setup. I will try other pads and go from there. The reality is that the pfc1038 us a street pad, so staying on the brakes longer indeed could be the problem.

10gt61
12-19-2015, 06:34 PM
Just so happens I have some Hawk HT10 front pads and Hawk Blue rear pads, new in the box. I'm not competing with the car next season, so if interested, let me know!

Grant Galloway
12-19-2015, 06:52 PM
I have the same problem with my car (2010 Civic si)

I run stock rotors, XP12 pads, SS lines and Motul 600

After a session I let things cool and pump the pedal with the engine off, to get the pedal hard. I wait about 5 mins to ensure the pedal is still hard!

I bleed the brakes every track day, and have done it between sessions at the track as well. My brake temps after a cool down are usually 700F on the Rotors, going to brake ducts this year..

Also have thicker Honda Accord Rotors, Calipers and larger pads for this year!

Grant

LVPBMW
12-20-2015, 11:56 AM
I had this problem on my E36 running several different fluids, Motul included. I found myself having to bleed frequently. I switched to Endless RF650 (Paragon Competition carries it) and did three weekends on the brakes without bleeding. Then I sold the car :).

Car was a 1998 328i, near stock weight, stock brake setup, running PF Z-rated pads with brake ducts to the back of the rotors.

Now, the Endless stuff isn't cheap, but it's somewhere between the Motul and Castrol prices. I have the stuff in my new track car and we'll see how far into the season it goes.

Dave Barker
12-20-2015, 03:38 PM
Certainly sounds a lot like a fluid issue. BTW, since switching to Castrol SRF, I rarely if ever bleed the brakes on my 04 Z06, even with the tiny 12.8 " rotors and my home made ghetto brake ducts. Doesn't matter if I am on Carbotech XP 10s or 12s or Raybestos ST 43s.

Don't have any idea how hot my rotors are getting but they sure crack with regularity.

Slowpoke
12-20-2015, 09:21 PM
Good point on the MC pressure. Hadn't considered that.
What's the usual solution there?

On my Subaru you adjust the free play behind the pedal. A Mustang guru should confirm if yours is the same. Running less fluid in the reservoir won't help at all.

boro92
12-21-2015, 12:45 AM
Ok thanks for the tips, everyone. For the record, i am currently driving a b8 s4. So thats about 3900lbs with 345x30 rotors in stock sizing. I have tried srf. Next up will be some ducting. But based on everones experience, this should not happen? Pedal will not get soft after sitting in the pits after a 20 minute session on smp long?

Slowpoke
12-21-2015, 06:59 PM
I have more hp, 700lbs lighter, ducting, Stoptech 355, SRF, pedal NEVER gets soft. It was back in my stock Brembo caliper days with inadequate pads, the only time that happened.

boro92
12-22-2015, 02:53 AM
Ok cool thanks for the update. Will be trying pagid rs19 next and some ducting. Fingers crossed it will work out! Ordered 4 bottles of srf. Fingers crossed i will only use 1 this season :D

10gt61
12-27-2015, 03:08 PM
my home made ghetto brake ducts

Dave, what did you use for the ducts? I've had Ford Racing brake cooling ducts on the Mustang since 2012, so the ducts themselves are pretty much shot by now and need replacing.

Dave Barker
12-28-2015, 09:10 PM
Dave, what did you use for the ducts? I've had Ford Racing brake cooling ducts on the Mustang since 2012, so the ducts themselves are pretty much shot by now and need replacing.

Just some cheap plastic ducting either from Cdn Tire or BusyBee tools. Crappy 2.5" but placed in a high pressure pick up area on the front of the car.

Doesn't seem to get hot enough to melt any of these cheapo ducts and is way cheaper than the fireproof stuff.

BTW, for my car, it seems to do better without a sealing type plate that keeps the air centered on the opening of the hub. I just use some metal pipe attached to the upright and aimed at the centre of the rotor. I had more trouble keeping rotors from cracking with the plates in place vs being open. Those sealing plates work great when you are moving but hold in heat when stopped. Seems for me that rotor cracking occurs during the cooling phase (you can sometimes hear the loud "ping" when sitting in the pits) and I assume that is due to asymmetric cooling of the rotor.

kmorris
12-30-2015, 12:40 PM
Just some cheap plastic ducting either from Cdn Tire or BusyBee tools. Crappy 2.5" but placed in a high pressure pick up area on the front of the car.

Doesn't seem to get hot enough to melt any of these cheapo ducts and is way cheaper than the fireproof stuff.

BTW, for my car, it seems to do better without a sealing type plate that keeps the air centered on the opening of the hub. I just use some metal pipe attached to the upright and aimed at the centre of the rotor. I had more trouble keeping rotors from cracking with the plates in place vs being open. Those sealing plates work great when you are moving but hold in heat when stopped. Seems for me that rotor cracking occurs during the cooling phase (you can sometimes hear the loud "ping" when sitting in the pits) and I assume that is due to asymmetric cooling of the rotor.

Aircraft Spruce (aircraftspruce.ca) is a good source for ducting - they have some pretty hi-temp stuff that is not too expensive. They are also excellent for hardware (mil-spec bolts, rivets, AN plumbing, etc) and composite supplies (cloth, epoxy, etc) and a myriad of other stuff catering to the aircraft homebuilder, which overlaps a lot with race car fabrication. Also they ship quickly from their warehouse in Brantford and sell in $Cdn.

Boekdrukker
12-30-2015, 01:04 PM
If the issue is boiling fluid, Castrol SRF will cure it.

Have tied, Motul, ATE, AP, Brembo,.. Always thought SRF was too expensive.

Previously, bleed brakes for each weekend, now I bleed it once per season.

Slowpoke
12-30-2015, 02:34 PM
I used semi-rigid dryer duct in the past. You can squish it to "oval" shapes to get around frame rails and tight areas without it completely collapsing.

https://www.lowes.ca/flex-duct/imperial-manufacturing-group-outdoor-exhaust-dryer-vent-kit_g1199044.html

TheJuggernaut
12-30-2015, 03:42 PM
One thing that might be worth trying is a tip I picked up from a Pagid racing engineer at PRI - try a ceramic pad, it insulates the caliper very well. But you may start cooking rotors.

Also if you can, try a thicker rotor or one with narrower vanes. He said at one World Challenge race in Montreal, one of the teams they were supporting had problems with the brakes where there are no significant straights to cool the brakes before the front straight and the brakes were overheating. They are limited by spec to brake sizes so they tried a rotor with narrower vanes (thicker rotor faces) and the brakes worked. They ended up winning because the others had the same problem they had and through the course of the race their drivers were able to brake consistently deep.

That was a bit of an eye opener for me too, looking at the rotor as a heatsink - its job is to store the energy from the braking until it can be dissipated on a straight.

boro92
01-06-2016, 12:30 AM
One thing that might be worth trying is a tip I picked up from a Pagid racing engineer at PRI - try a ceramic pad, it insulates the caliper very well. But you may start cooking rotors.

Also if you can, try a thicker rotor or one with narrower vanes. He said at one World Challenge race in Montreal, one of the teams they were supporting had problems with the brakes where there are no significant straights to cool the brakes before the front straight and the brakes were overheating. They are limited by spec to brake sizes so they tried a rotor with narrower vanes (thicker rotor faces) and the brakes worked. They ended up winning because the others had the same problem they had and through the course of the race their drivers were able to brake consistently deep.

That was a bit of an eye opener for me too, looking at the rotor as a heatsink - its job is to store the energy from the braking until it can be dissipated on a straight.

Ok wow interesting. Didnt expect this as 2 piece rotors usually have better air gap for the vanes but not necessarily any more thermal mass. Sometimes less thermal mass even. Here we have a team which opted to increase that aspect of the brakes at the expense of the ability to pump more air through the rotors. Hmm! Do you know if the races they were referring to restricted the teams to use stock size brakes?

TheJuggernaut
01-06-2016, 09:21 AM
Ok wow interesting. Didnt expect this as 2 piece rotors usually have better air gap for the vanes but not necessarily any more thermal mass. Sometimes less thermal mass even. Here we have a team which opted to increase that aspect of the brakes at the expense of the ability to pump more air through the rotors. Hmm! Do you know if the races they were referring to restricted the teams to use stock size brakes?

Yeah they were limited by the regulations (not sure if stock but he said they weren't permitted to go thicker). I'm sure given the choice they would have gone for a thicker rotor with the same gap but it turned out to be more important to have the thermal capacity than airflow (of which there is likely not much to speak of through the twisty, braking intensive section).