Give me a brake!
Back to Tech

It seems that we’re often so concerned with how our
sports car runs and looks that we almost lose sight of
perhaps the most important part of it, i.e. the braking
system.  It stands to reason that no matter how well a
car accelerates or how good it looks, if you can’t get it
slowed down, everything can and usually will become
a moot point.  The braking system in also especially
critical in a sports/racing car as the deceleration
capability is as important as any other aspect of the
vehicle’s performance envelope and is frequently
pushed to the absolute limit.  
Brake systems have evolved from crude friction
devices, normally made of wood, acting on the rear
wheels or driveshafts of farm carts and early motor
cars, to the use of multiple piston, multi-caliper, multi-
hydraulic circuit,  vented disc brakes at each wheel on
some of today’s more sophisticated automobiles.  (TR-3
owners take pride since that model was among the
world’s first to use the new aircraft-type “spot,” or
“disc” brake.)  These two extremes and every other
type of braking system does the exact same things
albeit through different means, that being the
conversion of the energy built up in the momentum of
the moving vehicle into a different form of energy:  
heat, which is produced by the friction material
against the braking surface.  That’s right; it’s as
simple as that.  It also makes a little sense, since heat
is really what gets the vehicle moving in the first place
through the combustion of the fuel and resultant
power or energy produced by the engine which is
correctly called in engineering terms, yeah,, you
guessed it, a “heat” engine!  Modern day vehicles, and
even the not so modern ones that most of us take
great pride in owning and driving, have hydraulically
operated brakes at all four corners (3-wheeled BMW,
BSA, etc., owners take exception!).  These are either
drum type or the previously mentioned disc type, or a
combination of the two, that being discs in the front,
drums in the rear.
It is the hydraulic part of the brake system that I
would like to discuss first, the basic principle being
quite simple to understand.  Foot pressure on the
brake pedal mechanically pushes in on a piston in a
fluid chamber in the master cylinder, transferring that
pressure hydraulically through the brake pipes and
hoses to the wheel cylinders and/or calipers where it
is changed into mechanical movement through the
piston in that cylinder/caliper and ultimately moves
the brake pad or shoe against its respective disc or
drum.  When the brakes are used very hard, many
hundreds of pounds of pressure are generated in the
hydraulic system so it should be obvious how
important the integrity of the entire hydraulic system
is.  As a chain will fail at its weakest link, a hydraulic
system is only as good as its weakest point.  For this
reason I try to look at the overall brake system
whenever I encounter a problem such as a “swollen”
flex hose or a leaking wheel cylinder seal, etc.  Often
times a particular problem may be a good indicator of
the condition of the rest of the system, e.g. if the rear
wheel cylinders are full of the “black slime,”  then the
entire system is likely contaminated.
Back in 1968, when the Federal government took one
of the first major steps in enforcing requirements for
safety related equipment in all new cars sold here, one
of those that I personally feel made the most sense
was the requirement of a “dual” braking system.  This
consists of a split hydraulic system with two or more
separate circuits in order to provide a backup system
in the event of a failure of part of one system.  I have
had exactly one experience with the sudden and
immediate failure of the brakes in a single circuit
system in one of my personal vehicles years ago, and it
was truly one of the scariest moments of my life.  Only
through the grace of God and the fact that I had
serviced the vehicle three days prior, including
adjusting the hand brake, did I avoid hitting the rear
of a motorcyclist stopping for a red light.  
Dual circuit braking systems also allowed the designer
another variable in proportioning the pressure
between the front and rear systems by using different
sized bores in the master cylinder to produce different
pressures, this usually being done by changing
caliper/cylinder bore sizes and swept area of the
friction surface.  Some cars take proportioning a bit
further with a mechanism that determines the
amount of load on the rear wheels and restricts the
pressure on the rear brakes as the vertical load
decreases, which reduces the adhesion and would
ordinarily promote rear wheel lockup.
As far as the “nuts and bolts” of the brake hydraulic
system goes, I’ll leave that up to the workshop
manuals.  I do want to elaborate on what the
instructions all say in regards to cleanliness and the
condition of the cylinder bores.  The hydraulic fluid
used in most braking systems is very good in all
respects except for oneit absorbs water.  If you want
to see how well it mixes with water, put some on your
hand and then try to wipe it off.  It still feels oily,
right?  You rinse with plain water and it will come
right off.  (Not only does it make good hand cleaner,
but it is also an excellent paint remover!)  Anyhow,
due to its affinity for water, the fluid must be changed
at least every two years.  Please use Castrol LMA         
type fluid.  The fluid is designed for use in systems as
ours using natural rubber seals and the “LMA” stands
for its :low moisture absorption” properties.  Moisture
in the system will cause rust to form internally,
especially in the cylinder boxes.
This brings us to the next point that I would like to
emphasize.  If you all attempting to rebuild a
hydraulic cylinder and you get to the part in the book
that says something like “inspect the bore for pitting
which would render it unfit for further service,” I
would advise you to heed that advice.  Pitting of the
bore surface is not acceptable, period!  It will simply
tear up the new seals prematurely and ultimately
require correction.
An alternative to replacing a cylinder with a pitted
bore is the process of having it bored out oversized
and sleeve pressed in, this, in turn, being honed to the
original bore size.  The choice of material for the sleeve
is usually brass, due to the non-corrosive properties it
has and the relative ease of machining it.  The other
option is stainless steel which is virtually bulletproof;
however, it is rather difficult to machine properly
hence more expensive.  Long term tests that I have
done for over fifteen years have shown that brass is
quite satisfactory.   It does, however,  suffer from a
tendency to become rather heavily “burnished” over a
long period of use; whereas, stainless will certainly
outlast every other bit of the car.
Next month we’ll discuss the parts that do the actual
braking, the friction surfaces and related bits.

Safety FasTR