Car Craft brake series/how to design a braking system

[Last Indian]

When I was in high school Carrol Shelby had a huge impact on me! Especially about braking & handling! But of the two braking! The story of his feud with Ferrari is well known. In that feud the story of the brakes is what impressed me.
So If you folks have an interest I could present a post about how to determine & or design the braking system you want! This will be an extensive article that has all the math & explanations that are very helpful. All of this is from a series of articles that came from Car Craft in 1981. If there is an interest it will take some time to digitize the information. All of this is what I used to design & build my own system from scratch for the “69” Z. As well as the system I have on the Indian.

 

Step-by-Step Guide: Upgrading Brakes with CTS-V Calipers

Brake upgrades for Gen2/3 W-Body Vehicles - MORE TO BE ADDED

[Jasmindont]

there's always an interest of the archival and preservation of information on here! Especially for a youngin such as myself who wants to learn this stuff

 

[Last Indian]

Braking! Now here is a subject that has as many opinions as there are systems that can be adapted to one platform. So it’s not a case of better or worse, but of fact from fiction when compared in relative comparison!
This can be defined as a simple case of math, money & looks!

I’ll explain it like this. In nearly all, if not all of these systems there are no plug & play choices, except for the OEM setup! Which arguably needs help, as it is inadequate even with ABS. So they all require an additional change to be completed, I.E. bigger wheels, different hardware beyond the calipers & rotors. In many of the cases when you do the math the stock system with some well planned upgrades will accomplish the same thing! Literally the same stopping power!
So bigger isn’t better necessarily! If you are adding larger wheel diameters & you what to fill that added space for looks, than bigger looks better, but the added weight won’t help anything for the unsprung suspension! And that increased unsprung weight impacts stopping distance as well as handling. If handling isn’t your goal & looks only is; than bigger is the way to go! Still if stopping in the shortest distance is your goal & handling is part of that goal than bigger is only better if you can make the added unsprung weight a non issue. Otherwise you might want to consider other options, like making the factory system way better by a few modifications that will shock you by their results.

So using the series’s of articles from Car Craft you can actually sit down and build a system different ways & see exactly how they compare & never spend a dime before you decide.

In this post is a series from Car Craft Magazine that was published starting in late 1981 & finished in early 1982. In early 1981 I had started designing a completely new, from the ground up brake system. This was to be a four wheel disc brake system. Of which few existed at the time. The Camaro, ironically was one with a RPO JL8 option, but I wanted something different! Something with less weight, but stronger, with better stopping power, more reliable & most of all less brake drag! This series, High Caliper Braking was a most timely article for me & helped me do the real upfront engineering work I needed to complete that task.

One last thing. I’m not making an argument for anyone else to do what I did That said the braking system in the Indian is a modified version of the stock OEM factory setup. I made this choice based upon what I knew I wanted to change. Then comparing those changes to both the GXP setup as well as the F body setup. After which I found there to be no negligible difference except in unsprung weight! The factory setup is lighter. I mentioned this before elsewhere on this site. That once I finished this systems modifications the Indian stopped nearly 40 feet shorter @ 70 mph & even hitting the brakes at lower speeds really hard the car would just stop! No ABS would come on.

Here is a comparison of the front GXP caliper square inch area Vs the stock caliper square inch area. Also included is the weight of each caliper & bracket, as well as the weight of the rotor for each. You will notice the sq inch are virtually identical & the total weight of one front wheel assembly, caliper, bracket & rotor is almost 9# per wheel.

GXP caliper (2 piston @ 45mm =4.93 sq.”)(10.8#) rotor (vented 23.8#) per side
97-03 caliper ( 1 piston @ 2.5 (63.5mm = 4.91 sq.” )( 13.2# ) rotor ( solid 17# ) per side

There were other modifications to the system, but that in general is not the intent of this post.

 

[Last Indian]

High Caliber Braking part 2

I will add this caveat to the last post. While I doubt anyone else will be crazy enough to attempt to do the things I did with this, it may offer some insight as to just how much effect can be had on braking, among other things, simply by looking at what can be done as opposed to what did everyone else do.

Back in the day I asked the simple question; why a square O’ring? That literally defies logic as well as the whole principle of O’ring physics! The GM engineer said it was to help in retracting the piston after release. That statement made no sense to me. What keeps the pistons from retracting are the residual check valves in the master cylinder. So the system I built for the Z used round, small cross section O’rings! I also eliminated the check valves from the master cylinder.
So why square? Well one reason would most likely be what I explain below.

My father in law worked for Gould Ocean Sea division. In the day they made the Mark 48 torpedo, a very sophisticated piece of warfare. This piece of equipment used lots of O’rings. This piece of equipment when being assembled mandated the use of thimbles for O’ring installation! If a employee, which was union, was found to not use a thimble, it was cause for termination. In this way the use of standard O’rings could present an issue for manufacturers of brake calipers. Square O’rings do not present this problem.

(Side note) O’rings in general are thought of by most folks as a gasket! They are absolutely not! They are actually a mechanical device! Not a butyl seal! Look at a actual O’ring sometime & notice the thin line that runs around it’s outside& inside diameters. This is not a mold parting line as most believe! It is the actual sealing point of the O’ring! If you look at a engineering print of an O’ring this projection line is defined as .005 wide by .003 high! You do not define a mold line! If you ever delve into to the mechanical application side of an O’ring in detail you will soon fined out that there is specific manner in which you install an O’ring! If you don’t pay attention to how they are installed, & you twist the O’ring, I.E. spiral it because you don’t use a thimble; they will leak like a sieve. Additionally you should always use the smallest cross section O’ring you can for an application. There are certain considerations for larger cross section O’rings! Heavy horizontal applications is one!

So my approach for the OEM brakes on the Indian was straightforward! Make the piston size bigger! When you start compounding surface area, even small increments add up quickly. Going from a 2.5 inch piston to a 2.75 inch piston took the square inches from 4.91 to 5.94. At that bore diameter that just barely gets rid of the groove from the square O’ring, .125 of an inch on a side. So there is plenty of wall thickness left! Now we make a stronger, more stable piston! How? Well now the piston will carry the O’rings instead of being cut into the side wall of the bore. And I used three of them! The first one .425 below the top edge where the dust seal sits. The bottom one .250 from the bottom & the middle one, well mid way between the two. This along with .35 coefficient friction # pad & special cross drill rotor, a bigger bore master cylinder & last but not least a 6.5 to 1 pedal ratio made for a phenomenal braking system. All of this without changing brackets or rotor size. And while I did eventually go to 18” wheels I did this originally using stock 16” wheels & tires.

 

[Last Indian]

My last two cents on brakes, then I’ll stop! Oh I kill myself ! I’m not arguing for or against any brake changes, upgrades! Whatever someone determines they want or need, they are in the best position to do so. They know what they’re going to do with the vehicle.
That said, I do believe a lot of folks who do them fall into one of three categories.
1. This sounds great! Bigger is better! Well, its actually not! I’ll get to that in a minute.
2. Their OEM system was never designed right & they don’t know that they can make it a completely different system through a few changes.
3. They understand the physics, AKA, math of the whole thing, including coefficient of friction for the pads as well as the tires, plus they know the metallurgy of the rotors to determine that the coefficient differential of pads & rotors is right, etc. etc..

Here’s a question, does anyone know the purpose of cross drill rotors? And are slotted rotor, whose slots don’t actually go all the way through the rotor, as effective as cross drilled?

Why bigger is only better under certain circumstances. Racing or continuous hard braking applications. Why? As I said before, because of the weight! That weight actually increases the distance needed to brake! So it is to a degree a trade off. You can actually find lots of articles that address this.

Once manufacturers went to semi metallic linings coefficients went out the door. They did this to CYA! For brake fade! Yet the problem was, until recently, rotor composition. Coefficients are based on dissimilar materials & coefficients, but semi metallic pads are virtually the same hardness as cast iron rotors. Anybody who knows anything about motorcycle brakes knows what works with semi metallic pads! Hardened rotors! Yet these don’t stop better! They simply holdup way longer against brake fade! That’s it! That’s the caveat! OEM’s went to bigger systems for this one reason! Coefficients are a brake killer. Coefficients can have as big of an effect on brake physics as rotor size or piston diameter. So to compensate for poor coefficients, I.E. pads & rotors are nearly identical in hardness, they went bigger. What they accomplished was to greatly reduce brake fade by semi metallic pads, bigger rotors compensate for poorer stopping power & who cares about warped rotor or worn out rotors! The car will be out of warranty in most cases before there’s an issue for the factory warranty. Additionally this why aftermarket warranties don’t warranty brake issues like wear or warping.
Case in point, I have two Lacrosses with the bigger rotors & the calipers appear bigger, but the piston in those calipers are the exact same size as the Grand Prix’s! They in stock form stopped no better than the Indian in stock form! With the changers to the Indian’s brakes, they don’t come close to stopping as well. Three years ago I redid both Lacrosse brake systems. New OEM rotors, which are the cryogenic treated rotors & different pads, a little softer, but still ceramic. Now they stop more like the Indian.
So basically it goes like this. X mass takes X frictional resistance to stop in X distance! In the case of braking systems that frictional resistance is pad & rotor metallurgy coefficient differentials.
Attached is a picture of the brake rotors I built for my Z back in “81”. These rotors were built from 1060 hot roll plate. These rotors & pads had 100,000 miles on them! Believe it or not. The rotor were never turned. The was next to no wear on the rotors & the pads were still had about 3/8s of their life left. This is how brakes should work.

 

[Last Indian]

The final part in the series is probably one of the most overlooked. Master cylinders & their configuration. A change in a system of any of the components can be impacted by the master cylinder. Say you change to harder pads & nothing else changes! Let’s suppose for the moment that those new harder pads will work just fine with the rotors you have, but the fact is if you go back to the previous parts of this series you’ll see that you know need more PSI!! Yet your old master cylinder is still delivering the same pressure as before. Just one example.
I hope you all enjoy this series from Car Craft! In the day they were right up there with Hot Rod & Popular Hot Rod.magazines.