Spongy brakes after track day, but not while on the track.

[SpeedracerIndy]

I did my third track day this past weekend. I still have a long way to go before hanging with the A and B groups, but I was very pleased with my progress. I was permitted to go solo by the end of day 2, so I took that as a good sign.

After the last session on day 1, my brake pedal was a little spongy but still had plenty of bite. Then, after the last session on the second day, and some very hard laps, the pedal would almost go to the floor.

I assume this is from boiling the fluid. What I found strange is that I never noticed any brake fade while on the track. I thought if you boiled the fluid, you would lose brakes on the track or begin to notice fade. Also, when I inspected the brakes after I got home, the dust boots on the rear calipers were almost completly burt off. The fronts looked ok.

The car is on standard SC brakes all around with ~5yr old rubber hoses, freshly rebuilt calipers and stock 30yr old rotors. I had fresh Motul 600 in there, and Hawk HP+ pads.

To begin to address my problem I have a set of Carrera rotors and calipers for the front, along with a caliper rebuild kit for the rear, new rotors for the rear and new rubber brake lines all around. I also plan on attending many more track days so that I become a better driver and am not getting on the brakes too soon and over heating them!

I was also thinking about taking off the baking plates (?) on all four corners and adding some kind of cooling, not sure what though.

Can anyone tell me if I'm on the right track, or am I trying to solve the wrong problem with my brakes? Thanks!

[wildcat077]

Any kind of brake cooling will definitely help ... Ajusa sells a bolt on brake cooling kit for the front of the 911's although with a stock 911 it's the rear brakes that generate more heat.
Removing the backing plates will help and if you look on the Rennlist forums there's a few threads regarding brake cooling !
You could also upgrade to Motul RBF660,i believe it has a higher boiling point ...

Track days are addictive,aren't they

Cheers !
Phil

[David in VA]

Don't forget to upgrade your fluid, ATE Gold or blue is a good alternative. Castrol SRF is even better but much more expensive. Everything else sounds good, I would suggest OEM for the rubber lines. Don't think stainless braided really gets you anything other than looks.

[djbrand1]

Yeah, for these brakes stock brakes get as much cooling on them as you can. I run some ducts that mount under the front control arms and have a backing plate with a hose that dumps the air into the center of the disc, so the cool air flows out threw the vented disc and not just on the inside pad area. For the rears, I don't know if I've seen a cooling kit, but im sure you can mount some kind of scoop. I've had the same problem with the rear caliper dust boots disintegrating quickly. I think part of the problem is it is very difficult to get those rear boots seated in the caliper correctly.

[aston@ultrasw.c]

I don't even bother to fit the outer dust seal any more. I do replace the inner seal with every pad change.

X2 on cooling ducts. Stock rotors are just fine with PFC97 pads.

In my experience vaporizing the brake fluid (or the water that is absorbed by the fluid) happens when you release the brakes and the pressure drops. You find out about it when you go onto the brakes at the end of the next straight.

Never had any issues with Motul 600.

[ivangene]

here ya go:
Pelican Parts.com - Brake Rotor Cooling

Motul most likely wont boil unless you are really riding the brakes. Try harder braking but less of it, get off the brakes as early as you can.

I am on Pagid Blacks and although I just came off stock Textar's i never had this issue AFTER I changed fluid to Motul

try a brake bleed, its simple and cheap to do...some people bleed after every session (seems excessive) - but after every track day isnt too much IMO

[aston@ultrasw.c]

Originally Posted by wildcat077

although with a stock 911 it's the rear brakes that generate more heat.
Cheers !
Phil

I didn't know that. Do they generate more heat or simply have less opportunity to lose it?

I made up some ducts for the rear but never installed them because I felt the scoops under the car were asking to be torn off.

However, I am about to install lexan rear quarter windows. Someone suggested that I install NACA ducts and route the air to the rears. Not a bad idea.

[michael lang]

I don't believe the problem is in your car's brakes. I believe the problem lies in your technique and I think Ed was on the right track when he suggest you make a change in your braking. With this having been only your third track day, you are not going nearly fast enough to really exploit the full potential of the stock brakes on your car. My suggestion would be at your your next event, talk with your instructor and have him watch your feet movement. Have him focus on not only application of the brakes but also on how you are releasing the brake pedal. I think you will find if you get someone to watch that part of your technique and make some suggestions for improvement, your brakes will hold up much longer.

[gchappel]

I have an 85 carrera and the first year I tracked the car I was SURE I needed a brake upgrade- was going to go all the way to big reds. My mechanic basically refused until I learned to drive. After about 10-15 track weekends my brakes were suddenly ok- yup in the A group as well. If your system is functioning properly- it is not the brakes. ( Although any cooling will not hurt)
Please do not take this the wrong way- but get an instructor back in your car. 2 days of training- you may be safe, but unless you are talented you will not be fast. Can't stay with the A group- how are you going to learn? Braking incorrectly? There are hundreds of little things to pick up. It is tough to do sliding around on your own.
Lastly- WHAT WERE YOU THINKING? Brakes spongy, almost going to the floor- and you went back out on the track? Our cars try to talk to us for a while- but if we do not listen...
Please, as soon as you start to feel your brakes fading, slow down and come in or at the end of one of the straights you will have no brakes. Spongy can go to nothing real fast. Learn to bleed your brakes- I can do it in 15min without removing the wheels (use speedbleeders)
Enjoy your car, but it wants to run with the A group as well.
Gary

[wildcat077]

Originally Posted by aston@ultrasw.c

I didn't know that. Do they generate more heat or simply have less opportunity to lose it?

I made up some ducts for the rear but never installed them because I felt the scoops under the car were asking to be torn off.

However, I am about to install lexan rear quarter windows. Someone suggested that I install NACA ducts and route the air to the rears. Not a bad idea.

We measured brake temps on the stock front and rear rotors and calipers with a pyrometer on my friend's 88 Carrera after a 30 minute run and compared with mine which has 996TT brakes all around and found the stock brakes to have generated more heat in the rear as compared to mine which generated more heat in the front due to the heavy front bias.

Stock brakes are plenty good enough but if you want trouble free weekends without having to worry about pad transfer and boiling brake fluid then an upgrade to larger brakes is a good idea.
After our runs i just contemplate the lovely hues of blue and purple on my buddies's rotors while i park my car and wait for the next session

Although i'll admit to being in the process of fabricating a front brake cooling setup for my car !

Cheers!
Phil

[911-32]

Originally Posted by gchappel

I have an 85 carrera and the first year I tracked the car I was SURE I needed a brake upgrade- was going to go all the way to big reds. My mechanic basically refused until I learned to drive. After about 10-15 track weekends my brakes were suddenly ok- yup in the A group as well. If your system is functioning properly- it is not the brakes. ( Although any cooling will not hurt)
Please do not take this the wrong way- but get an instructor back in your car. 2 days of training- you may be safe, but unless you are talented you will not be fast. Can't stay with the A group- how are you going to learn? Braking incorrectly? There are hundreds of little things to pick up. It is tough to do sliding around on your own.
Lastly- WHAT WERE YOU THINKING? Brakes spongy, almost going to the floor- and you went back out on the track? Our cars try to talk to us for a while- but if we do not listen...
Please, as soon as you start to feel your brakes fading, slow down and come in or at the end of one of the straights you will have no brakes. Spongy can go to nothing real fast. Learn to bleed your brakes- I can do it in 15min without removing the wheels (use speedbleeders)
Enjoy your car, but it wants to run with the A group as well.
Gary

Reread the original post Gary. He says the pedal went soft after he left the track. This is classic for SCs and 3.2s and was exactly what I experienced for years in my 3.2. The pedal is firm on the track and brakes are good, then you park the car for 40mins and find when you next get in the pedal is soft or goes to the floor. Pump the pedal and it firms up. In fact, get back out on the track and you have a firm pedal for the full session and great braking. I can only assume this is heat soak.

I had ducting to the rotor centres, hub block off plates, race pads (various) and SRF fluid. The brakes always worked and the pedal was firm on the track, but would get soft afterwards.

IMHO, sure you can struggle on with std brakes and you can bleed between session, use up the tiny std size pads in a couple of weekends and feel anxious about the soft pedal or upgrade. This is not only about braking technique - even the best racers with stock brakes drive around the issue and they are in race cars that are 100s of lbs lighter than road cars. There is no harm in the OP putting 3.2 rotors and calipers on the car. Its a cheap first step and might be enough. Personally, I gave in and upgraded to 964 size brakes - pads last more than a season, fluid is replaced beginning of the season and I never have to do anything else. Certainly worth the price.

$0.02

[Flieger]

It cracks me up how some people don't read the original post, or even the thread title.

( I have been guilty of this on occasion ).

[gchappel]

Oh,sorry. I actually did read the post. I have never seen brakes that were truly fine on the track but went nearly to the floor on the drive home. I stand by my statement however that if the brakes are spongy or the pedal nearly goes to the floor I would never take that car back on the track without at least bleeding the system. Pump up a soggy pedal and go back out on the track? Not this boy, anyway. Changing brake components is fine, and can clearly be a safety upgrade as long as you do not change the bias. It also can change your racing classification. When I tracked the Carrera we just bled every day and never had another problem.
Gary

[stuttgart46]

Good be worse if it was the other way around.
My 914 did that to me once after a DE weekend. I unloaded it and it sat in the garage for a few days before I drove it again. I jumped in and the brakes were spongy. Bled the brakes and they came back. I was running vented rotors and Super Blue with Pagid pads.
It never happened again.

[SpeedracerIndy]

Thanks for all the responses guys. 911-32 hit the nail on the head with my situation. Brakes are fine on the track and I had a nice high, firm pedal. After the last session of the day and the car had sat for a while the pedal became spongy. Heat soak sounds logical. I did my best to take the last lap as a cool down and not touch the brakes to let them cool, but the track is only 1.8 miles, so 2 minutes of cool down is probably not enough.

I am moving forward with replacing the fronts with Cerrera parts, and replacing the rear rotors. After 30 years and around 100,000 miles it can't hurt to start out with fresh rotors.

I also talked about it with my instructor and he didn't see a problem with my brakes. He said that with more practice I will be braking later into the corners and the problem would disappear.

What about the air deflectors that fit onto the A-arms and deflect air to the rotors. Where do you get those? They seem like a very simple but effective solution to get air to the brakes.

[ChrisBennet]

Over a decade ago, I ran a termocouple to the back of the front brake pad and discovered the greatest temps were in the paddack with it parked. It turned out that my codriver was using the brakes to stop the car in the parking spot. That leaves the brake pads up against that hot rotor.

To avoid this, coast slowly into the parking spot with the engine off, the car in gear and the clutch in. To stop, just let the clutch out and the drag of the engine will stop you. To recap:

1. Motor slowly toward parking space in 1st gear
2. Push in clutch
3. Turn off engine (but don't turn key so far that it locks the steering wheel)
4. When almost to parking spot, let clutch out and engine will slow you to a stop

Probably best to practice a few times someplace safe first.

[euro911sc]

LOL, Chris! Do you still let Mark drive your car?

Speedracer:

Braking systems are fun! Lots of good points here. SC's need all the cooling they can get. They have enough brake, but they need to be kept cool. I started out with some shop vac parts from home depot and now went to the full ducted setup. Search here and you will find dozens of DIY setups.

I am running a ROW SC and have moved to the Carrera fronts and rears. I was at Homestead 3 weeks ago and experienced what you have. I am running full front cooling ducts, HP+ pads, and RS683 fluid. Essentially, I was not loosing my brakes, but the pedal travel was getting longer. Post runs on the street the pedal is a lot softer.

After discussion with several guys , the general consensus is that the HP+ pad just doesn't hold up well at the track, but is great for auto cross. The DCTs (60/70) are awesome, but in Hawk's own technical book the HT10s and DCTs perform the same for the car's weight so save some $s and go with the HT10s.

I borrowed a set of Blacks (similar to HT10s) for a track day last year and did not have this issue at all. Though I was in a different susp. then, the only component in the brake system that changed was the pads. Additionally, there was a Carrera there running with me and he was on HT10s. He reported great brakes all the time.

So... given these data points I moved to HT10s on all corners. I'll be at Sebring this weekend for 2 days. We'll see how it goes!

On a fluid note, the Motul is good and so is the SRF. However, I am now running 683 and am very happy. It is the same stuff the Bullet car ran at Daytona.

-Michael