Since we had so much fun with cam timing..how about Brakes

[JeffYoung]

Kirk, thanks for making sure my precise (and self-chosen) dilemma is clear...lol.

Car is a 1980 TR8 that weighs more than a 240Z and has smaller pads and rotors (and nearly useless drums in teh back). I kid you not.

Chris, I hear ya. I do. Part of this is a driver issue. Last year I had no brake problems, but I was slow, and not really working the car. Now that I've gotten up to semi-speed, I am working the brakes much harder. And I need to learn to work within the parameters of what the car gives me. I've talked to a lot of people and we've run over the issue and over the issue and one thing is I do need to learn to brake less and more efficiently.

BUT..it is not like I'm resting on the pedal down the straights or braking for too long without much pedal effort. I've at least progressed past that point.

And, I'm using Motul 600, and just bought a can of that liquid gold Castrol SRF to try at Roebling next weekend. I've got Performance Friction pads and decent ducts and top hats. NOTHING is working.

I'm going to start carrying extra seals to races because I literally melt through the seals every race.

So, yes, Houston there is a problem and unfortunately Mission Control has not been able to come up with a solution.

But I'll keep working on it.

[Knestis]

I'm worried that you may just have a thermodynamic deadlock on your hands, Jeff. If the rotors simply don't have the surface area to shed heat energy fast enough, additional ducting may not make much of a difference.

The fact that the seals seem to actually be melting is not evidence that the fluid is pooping out on you.

If you do add more ducting, point it at the caliper.

How about some NASA thinking here, maximizing lots of little advantages to see if they measure up to a measurable benefit.

** Bead blast your calipers to rough them up - marginally increasing surface area - then apply a heat-shedding coating?

** Add a thermal barrier between the pad and piston?

** Thinking outside of the box again, how about brake pads with heat sinks built into the backing plates?

How do the rears hold up? Are you using all of the rear brake that you have available, as lame as they may be?

K

[Quickshoe]

Along the same lines as some of Kirk's comments.

A very smooth rotor surface does not have as much surface area as a "rougher" area. Don't know how much more agressive they would be on pads...never had the need to experiment that way. Heck didn't even need to duct my solid front rotors.

Perhaps someone with more knowledge than I can tell you how rough a surface you can tolerate before other issues arise.

Brake pads are free. Have you experimented with other brands?

How about wheels? Are there other styles of wheels that may allow more heat to escape? Is the problem worse with steel wheels versus aluminum wheels?

Good luck.

[m glassburner]

Rims...we havn't talked about those yet....what kind do you use?

[gsbaker]

Ducting is most effective when it maximizes air velocity.

A good friend is a mechanical engineer who does a lot of thermal work. He tells me the ability of air to remove heat from a surface varies with the cube of velocity.

Gregg

[JeffYoung]

Guys, many thanks for the thoughts. I'll try to answer your questions below:

1. Bead blasting the calipers -- never thought of that. They are off, so I might as well try.

2. Insulation between pad and piston. Kirk, I tried metal shims. HATED the pedal feel and besides, it didn't work. Had someone suggest smearing silicon on the back of the pad as an insulator. Will try that. Question for you: I'm a lawyer, not an engineer. I just sue people, and don't have enough experience actually doing somehing useful like building things. What is a heat sink?

3. I have not tried temp sensing paint on the calipers to see what is getting hot. Good idea, and I will try that.

4. Rims are Panasport Ultralights. About as good as you can get weight, air flow and heat transfer wise I suspect in 13" size.

5. I will duct the caliper, I have not done that previously.

6. I just installed a proportioning valve to make sure I am using the rears (I've gone a season and a half without significant wear on the rear shoes). So, up until mid-summer, I was not using the rears enough. Now, I am using them just short of the point of locking up the rears, and I'm still have the problems up front.

7. Pads. I've run Hawk Blues and the PFC. Much prefer the PFCs. Have not run the BLues since I started having these problems, maybe I should. Have not tried Carbotechs.

Back to the woodshed this weekend. Fortunately, Roebling is easy on brakes so I'm hoping I can make it through the weekend without a melt through.

Thanks again guys.

Jeff

[JohnRW]

Originally posted by JeffYoung:
I'm a lawyer, not an engineer. I just sue people, and don't have enough experience actually doing something useful...
Jeff

You guys ought to consider the wisdom of offering brake system modification advice to someone familiar with litigation procedures.

Some cars just have disadvantages 'built-in'. Unless we want a 'spec class', we'll all just have to live within the rules for fixed to the inherent problems.

[Knestis]

I wouldn't put much trust in Si gel behind the pads. I was thinking of dense Si shim material. We had samples that we used under integrated circuits a long time ago in a previous life, that came in different thicknesses and densities. Translating theory into a practical solution here would take some poking around.

A heat sink is a device with lots of surface area, intended to shed heat energy to the surrounding air. Since pads are free, you could have a backing plate - space and caliper design permitting - that put some metal out in the airstream, to cool the pads before they could transfer that heat to the pistons.

It's good to know about the lawyer thing, by the way.

K

[Tom Donnelly]

I use Hawk Black HT9 pads on my 240z. Ducts to rotors and calipers with a clamshell on the calipers (kinda like a tophat I guess).

And I have the pads riveted instead of just glued. The Blacks worked better for me than Blues. Brakes totally went away with the Blue. Still go thru rotors and pads and can have at least one 'Oh Shit!' per race.

Hawk phased out the HT9 so I'm going to need to find another. But that is what worked best for the 240.

Tom
'70 ITS 240z

[Tom Donnelly]

Kirk,

I was real interested in the velocity statement. If you could run a venturi of sorts in the ducting somewhere, that would increase the velocity, right? Like, scale down the ducting and scale it back out and that might create a low pressure area just after the 'pinched' part? Or is the air flow too erratic in flexible tubing or too dependent on vehicle speed to matter?

Tom

I looked back and saw it was Greg who mentioned velocity. Sorry about that Greg.

[This message has been edited by Tom Donnelly (edited October 01, 2004).]

[GKR_17]

Originally posted by JeffYoung:

6. I just installed a proportioning valve to make sure I am using the rears (I've gone a season and a half without significant wear on the rear shoes).

Where did you install the prop valve?

What compound pad have you been running from PFC?

[JeffYoung]

Prop valve is right after the master cylinder. I have two lines coming out of the master -- one that goes to the backs, and one that comes out, "tees" and goes to teh fronts.

I put the prop valve in the engine bay because I figured it was one less thing the driver could screw up from the cockpit. Adjust in between sessions and leave it.

On the ducts and venturis...so if I narrow the duct down right before the rotors...I might increase the velocity of the flow and the efficiency of the cooling?? Neat idea.

[JeffYoung]

Oh forgot -- compound was PFC 90, they've replaced it now with another compound..not sure what the new number is.

[GKR_17]

I'll have to check that shape to be sure, but it has probably been replaced with 97 compound - and is a lot better for IT than 90.

I should have been more clear with my question on the prop valve, what I meant was which circuit is it in? All it really does is limit pressure (while also causing some pretty nasty hysteresis). So if you don't have enough rear brake now, you don't want to add one to that circuit. And it's not a good idea to have one in the front circuit either.

Grafton

[Mark LaBarre]

Originally posted by JeffYoung:
..so if I narrow the duct down right before the rotors...I might increase the velocity of the flow and the efficiency of the cooling?? Neat idea.

Whilie the velocity may go up, you'll have a reduced volume of air due to the restriction. I'd opt for more volume any day for brakes.

[gsbaker]

I checked with my ME friend and discovered I was wrong: the power needed to move air, not the ability of air to extract heat, varies with the cube of velocity.

(We were discussing this one night during one of several recent hurricane parties here in central Florida. Alcohol was involved, which probably explains my error.

How geeky is that? "Hey, let's have a beer and discuss fluid mechanics!")

In any event, it turns out that Mark is right and velocity matters. Long story short, increased velocity improves heat extraction if all other things are equal but, as Mark mentioned, if you choke down the duct too much you begin to loose volume.

Sounds like a little is good and a lot is bad. I'll ask around more on this.

Gregg

[JeffYoung]

After pulling the calipers apart for the upteenth time, I decided to actually pay attention to what I found. Looks like the inside seal (meaning the seal on the inboard piston) is the only one that is failing....ducting to the caliper on the inboard side may solve this.

[Ron Earp]

I know that seal was crispy, but you might want to use those dust seals too. If a piece of crap gets between the piston and bore it'll cause the seal to fail in short order, in many cases.

[eh_tony!!!]

One guess I have is that the PFC pads are magnifying a marginal situation into a large problem. PFC pads tend to be very hard on rotors and generate high temps. We used crack a set of front rotors per race (and that's with a 6" duct and water spray) until we switched to the mintex.

Since your rotor/drum situation is marginal anyway, you may want to try something less aggressive (like a hawk black instead of blue).. Kind of an endurance pad with a lower torque.

Ducting to the calipers does make a big difference though

[apr67]

One other option.

Heat shields. Prehaps out of stainless. Bascialy a thin sheet of metal in the exact shape of the backer plate on the pad to discourage heat from travleing into the pistion. I belive it to be legal, because it is just an extension of the pad, a shim if you will.