Why You Might Want to Rethink Your Brake System

[Last Indian]

I have stated this before, Carroll Shelby in 1963 in his ongoing battle with Enzo Ferrari, took his AC Cobra from zero to 100 and back to zero in just 11 seconds. He could stop nearly as fast as he could accelerate. The average car today accelerates from 0-60 between 4 & 9 seconds & most stop substantially better than 20 years ago. Yet every deficiency in the braking system can reduce that number by a factor of 2. 

So in the spirit of sharing a little more than 50 years of doing brakes and almost 40 years of building custom brake systems, I will attempt to depart some how to advice that might be different than you are use to.

  First of all the coefficient of friction is the number one thing you might want to consider. This mathematical equation in physics is what stops a car, along with the mechanical advantage of the pedal, master cylinder piston diameter and fluid characteristics. 

So coefficient of friction is needed for the selection of rotor material and pad material. The difference between them is what can make or break the whole system. Most nearly all rotors are cast iron and as far as American cars, they’re all cast. There are many places that will explain brake coefficients, but it’s not as simple as their explanation if you want the best performance, durability and longevity. If you want these elements, it takes a great deal more to make those optimal numbers work.

Any of you that are old enough to have run 4 wheel disk brakes from the 1970s through about the early to mid 80s knows what those systems were like, they stopped great, but more than one or two hard stops and brake fade became an issue. So manufacturers turned to semi metallic pads, but did nothing with the rotors, bad choice. Sure they handled more heat, but longevity took a hit big time as did durability. Rotor warpage, runout. This still exists today! 

Ok, so the best is soft against hard, not hard against hard! That said, soft against hard generates the most heat. Why? Because work is heat/energy, you know the whole physics thing. The problem is the soft pad materials starts to break down under that higher heat which causes out gassing. And it’s that out gassing that cause brake fade. Why? Well it is literally a gas, so the gas acts as a barrier layer. It acts as a lubricant and the gas must be compressed out of the way first before pads can contact the rotor. The pad material also breaks down, while this isn’t as big of an issue as it may see at first, since it is at surface level and will be abraded away in the long term it may lead to pad failure, so it too should be addressed.

So what can be done? Ventilating the rotor in some manner helps with out gassing. Depending on how the rotors are ventilated can help both out gassing and aid cooling of the rotors and pads, which can minimize out gassing. Changing the rotor material to say C1018 hot roll steel with say FE pads will Change the coefficient, help stop better, run cooler and wear less. If they’re ventilated the system will be even better. The variables are endless.  My custom made set of brakes for my “69” Z were C1018 rotors that were cross drilled ventilated. The pads were .2 coefficient pads which I don’t think you can even get today. The calipers were three piston calipers set in double shear. This system was incredible! It was like throwing a boat anchor out. The car would just flat stop, no sliding, no skidding and the first time I took the car out to test them I stopped 100 feet short of the red light, no kidding! This system used special silicone fluid. These pads and rotors and fluid saw more than 110,000 miles with out a single maintenance need. This system was installed in 1979 and stayed on the car till it was sold in 2004 with half of the original pad material left and no real obvious wear on the rotors.

Next the master cylinder. Believe it or not there are a lot of master cylinders from different GM cars that will fit your specific car. Some will have different size pistons, some larger some smaller, some will have different configurations of the bowls. In the end different size pistons deliver more or less fluid and change the amount of pressure you can apply. An example would be this. A 1” piston replacing a 7/8” piston will deliver 15% more fluid which basically delivers more pressure, and yes this makes the pedal harder to push, but that comes to the next component for possible change. The master cylinder I ran in the Z was huge 1 1/8 bore piston from a Chevy truck.

Pedal leverage mechanical advantage. Changing the length of the pedal with relationship to mechanical advantage to the master cylinder piston drive arm placement. The brake pedal swings on a upper pivot shaft. Somewhere below that pivot shaft is another hole to attach the master cylinder piston drive arm. Changing that location towards or away from the pivot shaft changes the mechanical advantage, making it easier or harder to push the pedal. Also lengthening the overall pedal length and leaving the drive pin hole alone or moving it changes the mechanical advantage. Now moving those location points is no small task, as alignment, room and angles play a key roll. So one of the simplest things is lengthen the entire pedal, but leave the pivot shaft and piston drive arm locations alone. So in essence lengthening the section from the piston drive arm down.
Example, is you increased the master cylinder piston size, changing the pedal leverage mechanical advantage from 6 to 1 and making it 7 to 1 would move more fluid theoretically causing increased pressure, but with no greater effort. The pedal configuration I ran in the Z was completely changed to give a 14 to 1 ratio on the master cylinder. 
I ran no check valves in the master cylinder. I ran no proportioning valve and the junction block under the master cylinder that used a shuttle piston to alert you for front or rear brake loss was changed to just a aluminum junction block.

Brake fluid. This fluid plays a key roll in transferring power or energy from your foot to the brake pads. Yes they are all different, some in small insignificant ways other in very substantial ways. 
All except Dot 5 fluid are ester based or mineral based. Which mean they’re hygroscopic, absorbs water as well as hydrophilic, mixes with water. Brake fluid has two boiling points, one dry, no water. Number two wet, with water absorbed. For example a Dot 4 fluid has a wet boiling point around 300F or higher, but water boils at 212F. When water boils it becomes steam, a gas, and gas unlike liquid water is compressible which can cause brakes to stop less effectively, even anti-lock. So change your brake fluid at least every 2 to 3 years or every 15,000 miles. If you live in a hot humid climate or winter climate and don’t garage the car at all, this too will shorten brake fluid life.

Official D.O.T. Edge Code    Coefficient of Friction (C.F.) 
@ 250 F and @ 600 F    Comments
EE    0.25 to 0.35 both temps    0-25% fade at 600 F possible
FE    0.25 to 0.35 @ 250 F  
0.35 to 0.45 @ 600 F    2% to 44% fade at 600 F possible
FF    0.35 to 0.45 both temps    0-22% fade at 600 F possible
GG    0.45 to 0.55    Very Rare
HH    0.55 to 0.65    Carbon/Carbon only.  
O.K. up to 3000 F where it glows

 

 

Edited March 26, 2022 by Last Indian

[indymanjoe]

Thanks for posting, real world experience is great. 

[Last Indian]

On 11/12/2017 at 6:16 PM, indymanjoe said:

Thanks for posting, real world experience is great. 

Thanks Joe! If it helps someone to see away to improve their braking system then the post will have made sense. To me a quick car is a nescesity, a fast car is great, but today most cars are fast; to me, to stop under control in the shortest distance possible is paramount!