Brakes vs. Heat - Hypothetical (sorta) situation

[MysticLlama]

So Saturday on the track I cooked my brakes real good and didn't get them back for a few laps until they cooled down.

The obvious fixes would be bigger rotors, more heat resistant pads, more heat resistant fluid, and more cooling.

So let's assume that we can't do all of these things and I need to get a little more capacity out of the system by hacking it.

The first thing I need to do is change my braking style and conserve them a bit more, did that the last half of the race and it was working okay, but I still wasn't getting as much available brake as I'd like between cool down sessions on the straightaway.

I already have the biggest rotors I can fit on the front, so I can't go bigger.

I can't put cooling ducts in the bodywork for the front, and they aren't vented anyways, so it wouldn't help as much as it would on other vehicles.

So it leaves me with technique, fluid, and pads.

Technique I'll be working on.

Fluid I'll go for something good.

Now some heat questions I have...

Does fluid boil immediately at the point of the caliper, or would having extra fluid help any? For instance, if I put in a couple of coiled hard lines to add fluid capacity and act to cool the fluid faster would it help any?

Pads will only help keep the heat out of the fluid a touch longer, and not actually make the braking create less heat, correct?

I can more efficiently cool my rear brake, and have dual masters, so I could adjust bias one more notch to the rear, maybe that would help a touch?

Now that the questions sound really weird, I'll mention that it's a shifter kart and not a 911, but some of the concepts have to be the same, right?

[GrantG]

What about those titanium insulators that go between the pad backing plate and the pistons in the calipers? That might help. They also make some cooling ducts (scoops) that attach to the A-Arms and don't require ducting from the body-work...

[MysticLlama]

The titanium backers is a good idea, I'll see if I can find something to cut down to size.

Scoops won't work, I already scrape bottom a few places around the track.

[GrantG]

Here's some info on Ti heat shields for brakes:
http://www.seinesystems.com/TiBrake-Home.htm

[Jims5543]

Technique is very important. Most think getting on the brakes earlier will enable them to run cooler and that is not true.

Braking deeper and for a shorter time is actually better. A long soft brake just creates moe heat in the system. Getting on the brakes and off them efficiently is the best practice, along with good treshold downshifting to help shorten the brake zone.

I also find bleeding the fronts after a spirited session is almost mandatory. It is not uncommon for me to bleed 3 times in one day just for insurance. I am also assuming your using good pads and fluid.

[Superman]

Rob, the Boeing Surplus store, which I think may be in Kent....or Renton.....sometimes has sheet titanium. Ti is AMAZING in terms of its resistance to transferring heat.

Of course, in terms of technique, you would stay away from touching the brake pedal except when it's time to brake. When it's brake time, brake hard. Then release. The heat should largely leave your brake parts before it has a chance to get into your caliper. And of course, really clean brake fluid is necessary. It is quite difficult, probably impossible, to evacuate all the old brake fluid from the calipers when you bleed them. The bleeding process should probably include either removing the pistons, or at least working the pistons in and out of the caliper. Otherwise water is likely to stay in there, and water is the problem. I'd guess your brake fluid is not boiling. My guess is that there is water in your calipers.

[MysticLlama]

I know my technique needs work, apparently most people do this their first 3-5 races. I was doing a lot better in conserving them towards the end, and I finished instead of pulling off like most do, so I still did okay.

If I get some time I'll check out Boeing surplus and see if I can find any Ti. I'm guess it won't be the easiest stuff to cut up, but I shouldn't need anything real thick.

I was trail braking a bit too much I think, and not getting off of the pedal fast enough. I was waiting a ways to get on the pedal hard to brake late, I just wasn't getting back off of it efficiently.

A spin and then fishtailing lockup in the practice sessions had me a little wary of mashing them too hard, so I had to get my confidence back up in that respect, which then made me lose them. Couldn't win.

The calipers are small and easily accessible other than having to take the safety wire off to get them unbolted. I should be able to do a good full bleed before next time I go out.

[coloradoporsche]

Can you lighten the car? Just a thought.

FWIW, a lot of club racers in G class (like your SC) do well with stock rotors and calipers. I use the "under A arm ducts", and my car is really low. But you might find the 964/993-style diverters give you more clearance.

EDIT: Nevermind...I see you are talking about a go-cart. Maybe there is a forum for such things where you can find some better advice?

[MysticLlama]

Nope, can't lighten it, I was already 10lbs underweight.

Wasn't the 911, was a kart. My 911 has GTP-LW brakes and it's lightened and I'm spoiled to having never had heat problems since they went in.

Technically should probably be in the racing forum since it's not directly 911 related, but just looking for clever ideas that someone in here might come up with that could maybe help out everyone.

[911pcars]

"Does fluid boil immediately at the point of the caliper, or would having extra fluid help any? For instance, if I put in a couple of coiled hard lines to add fluid capacity and act to cool the fluid faster would it help any?

Pads will only help keep the heat out of the fluid a touch longer, and not actually make the braking create less heat, correct?

I can more efficiently cool my rear brake, and have dual masters, so I could adjust bias one more notch to the rear, maybe that would help a touch?

Now that the questions sound really weird, I'll mention that it's a shifter kart and not a 911, but some of the concepts have to be the same, right?"

Shifter kart or 911, if the brake fluid is boiling and:
- there's no moisture in the system
- your braking technique is per suggestions
- it's not old and contaminated
- there's no air in the system

..... then I would suggest using a BF with a higher wet/dry boiling spec. The best is Castrol SRF, but you may not need something that good (or you might).

Yes, fluid boils that is closest to the brake pad; less so the further away it is. For example, BF in the reservoir will be at around ambient temp. Fluid location is pretty static in a brake system. Some racers use a BF recirculation system. Not sure one could be adapted to your system, but why not? Try a circle track supplier.

Try fabricating some ti brake shields. Use only Grade 4 ti. The lower grades aren't as good in their thermal conductivity specs.

Over biasing the rear brake, especially with a short wheelbase frame such as a kart, might create more end-swapping.

Sherwood

[MysticLlama]

The amount of brake fluid it would take is really small, so swapping it out to something better wouldn't be cost prohibitive, so it seems like the first thing to try.

Will the brakes themselves work fine as long as the fluid doesn't boil? If I put it better fluid, it'll obviously allow the brakes to run hotter, is that okay?

Same question for the shields too I guess, even more heat will be in the disc/caliper at that point.

The biasing would make it more likely to spin, although a lot of karts have smaller fronts than this one, or sometimes not any at all, so it's a normal thing to have to get used to. It does have a nice big vented disc back there, that's why I asked.

[Jay Auskin]

Why do you need dual master cylinders on a SC? I have a '78 with a 3.2L. I run Performance Friction PF97 compound pads and never lose my brakes. Everything else is stock on the brakes. I had x-drilled rotors (because the PO put them on), and finally cracked them after one year. We have a track here north of Chicago that is REALLY tough on brakes (Blackhawk Farms).


BTW, a guy I know who does W2W racing said the Ti sheilds are useless.

[911pcars]

Here's a brake fluid chart I put together awhile back. Updated, 4/06:

http://members.rennlist.org/911pcars/brakefluid.htm

There's a drawback in opening a container of BF and storing the unused qty. While SRF is the best in not absorbing moisture, sitting on a shelf with a partially used 1 liter container will allow moisture to be absorbed. I would fill the partially filled can with marbles to raise the fluid level/minimize the air space in the container, then seal it tight. Maybe put it in an air tight zip lock bag.

You could try Motul RBF first. While its specs are only slightly less than SRF, it's less expensive, can be purchased at most motorcycle shops and the container is only 1/2 liter.

Sherwood

[Superman]

Yes, Ti is hard to cut. The thickness of the Ti might make new pad installation difficult or impossible.

My best suggestions are in the "conventional wisdom" category. Especially making sure all the old BF is removed from the caliper and replenished. The best way to do this is to rebuild the calipers. Short of that, I recommend bleeding with the pistons pushed all the way in, and then pumping them out, and pushing them back in and bleeding again. Maybe repeat again. Otherwise, you will still have water in your caliper. Beyond that, just learn to use the brakes ALL THE WAY at the right time, and then get your foot off the pedal. You want to minimize the time spent with the pad in contact with the rotor.

[MysticLlama]

I think that Speedware has Motul for something like $16, so I can try that.

At that price point, it's easy enough to just toss if I don't use it all. Only one more race this season anyhow, and I'm not sure just yet if I'll even make it or not, just looking for ideas to tinker with.

[Bill Verburg]

Use absolutely brand new fluid, once it gets hot enough to boil throw it out and start w/ new high quality DOT 5.1 fluid

Nobody says the scoop have to go under the car(T)


Notice the plenum that accommodates the whole rotor

See if you can get ceramic pads, they help keep heat out and will probably have an extra integral thermal barrier, mist of the new gen pads do.

unless you have recirculaters it doesn't matter how big the reservoir is once it's capacity is sufficient to service the slave pistons.

Do use as much rear bias as you can get away w/. You have too much when the rear locks first, the exception would be if the rear lockup helps you turn(depends on driver and course< not for faint hearted>)

If the wheels are solid try getting open ones, often they can be had w/ a spoke design that will pump air across the rotors.

[Emission]

Originally posted by Bill Verburg
See if you can get ceramic pads, they help keep heat out and will probably have an extra integral thermal barrier, mist of the new gen pads do.

I'd take this approach - go with a high-temp pad (you don't seem to have any issues getting them hot in the first place).

You can always lose weight (you, not the cart).

[MysticLlama]

Thanks for the good ideas Bill.

It sounds like there isn't much to gain in the recirculation department except when the other options have been used. Don't want to add something else to break either.

I'll see if there is anything I can do bodywork wise, but it's not my kart, so I'm limited to reasonable stuff. I'm thinking maybe a central inlet by the steering wheel might work well, since it's already in the airflow it should'nt mess with the aero too much, and I already have to get my feet under there, so it wouldn't be in the way.

Wheels are solid, hadn't even thought of that, I'll look around next time at the track and see if anyone has open wheels.

Emission- can't lose weight, I'm already underweight for the class and have to bolt in lead.