There
are two types of brake upgrades- and many different levels of equipment. From the cheap aftermarket pads you can buy
at any parts store to the top of the line carbon pads (and disks!). You have to decide which suits your style of
driving the best.
Although
drum brakes are quite good for grocery runs, but lack the heat dissipation
abilities of a fair set of rotors. Drum
brakes are not discussed here; If you have to use them (like on my Spitfire)
the general properties of pad materials and disk material will stay similar but
obviously the different techniques used on rotors cannot be used on drums in
the same manner.
Most aftermarket braking equipment is cheap, readily
available, and not much good at all for anything other than getting
groceries. The pad material glazes
easily, wears at a high rate, fades massively under hard continuous braking and
basically isn’t of much use in consistent hard braking.
Since the pads are so soft, they do provide almost 100%
stopping power when cold, and are great first thing in the morning. Three hard stops or so, and that power is
reduced. Also, the softness of the pad
is noticeable when trying to make the pedal as hard as possible- the spongy
feel of the pad can never be removed.
Aftermarket disks, generally foreign made cast iron,
allow for cheap replacement, but are also formulated for the softer pads- a
hard pad (anything other than aftermarket) will destroy the rotor in a short
amount of time.
The factory Toyota pads and rotors are quite good. They offer a very good mix of performance
and longetivity. The pads are hard, as
well as the rotors, and wear for quite a long time. Heat fade is less than the aftermarket pads, but once they are
gone, you won’t get much out of them.
Sport pads, such as the KVR and PFC road formulations,
offer better stopping power and much more resistance to heat fade. As with race pads, they need heat to work-
cold stopping power is very reduced.
However, heat fade resistance is increased dramatically, and bite is
nice and sharp once heated up.
For any sort of prolonged spirited driving, this is a
must have.
Many different pad compositions are available to suit
your needs. Performance Friction offer
a line of pads, two of which stand out in my mind- the 82 and 93 pads. For full race situations, the 93 composition
seems to offer the best grip with most heat resistance. The 82 pads are a bit softer and more
suitable for the average racer.
The problem with race pads is that they do not belong on
anything other than a full race car.
Cold stopping power is negligible- you need to run them up to
temperature before they have any grip at all.
Which, in layman terms, means that when you are backing out of your
driveway in the morning, you will have no brakes.
Three types of brake lines are available- hard lines,
rubber hoses and stainless hoses. Hard
lines are used for most long lines that do not flex. These should be secured to the chassis and not allowed to move
and fatigue. Use flare wrenches when
working on these fittings to reduce the chance of rounding the nut edges, as
the lines are difficult to replace.
Rubber lines are perfectly adequate for the amateur and
club racer, as a good set of proper lines will last quite a while. Inspect regularly and often for cracks or
exposed braiding. Since rubber lines do
bulge out a bit under pressure, the pedal will never feel perfectly hard. This is a help for many drivers, as
modulation of the brake pedal is easier, and more control over locking the
brakes is available.
Stainless Steel lines (Aeroquip lines) are available for
many applications. FWIW, unless you
notice the difference between a completely hard pedal and a slightly soft one,
you won’t get any great benefit, and if you are not a practiced driver, this
may hurt you a little- modulation of the brake pedal is an extremely difficult
technique to master. Advantages of
braided stainless lines are less expansion, better pedal feel, resistance to abrasion
and cuts. If you rally, there is no
other way.
There are three main types of brake fluid- DOT3, DOT4 and
DOT5.
DOT3 is an older specification. Qualities include low boiling temperature, lower fluid properties
and cheap cost. Don’t use it for any
sort of spirited situation unless you have nothing else.
DOT4 is the current road standard in the US. Most cars come with this fluid from the
factory. It is cheap, and a higher
boiling temperature, and is hydrophilic.
Hydrophilic substances are water loving- if you have water in your brake
lines it must be flushed out, which means bleeding the brakes. This should be done every 6 to 12 months as
a matter of course. Exposure to
moisture allows water to mingle with the brake fluid, making the pedal soft,
and under high heat, the water will boil, causing bubbles in the lines and the
brakes to cease functioning.
DOT5 is silicone fluid, a hydrophobic substance- it
repels water. This means that the
fluid is more stable, does not collect moisture and has the same properties
it’s lifetime. Moisture in the system
will accumulate at the lowest point in the system and cause that part to
corrode. Flushing the system is once
again recommended every 6 to 12 months, but can be prolonged. When changing from DOT4 to DOT5, the lines
must be completely clean and free of both moisture and old brake fluid.
Several
types of rotors abound, starting with thin disks, progressing to vented rotors,
and working through the many different types of slotting and cross
drilling. Everything under the sun is
available, some of it looks cool, some of it works, and some is even worth the
money spent on it.
When the driver presses the brake pedal, the hydraulic
fluid pushes on the brake pads through the piston, creating friction between
the pads and rotor. The friction slows
the car by turning rotational energy into heat. This heat also causes the gaseous pad material and air trapped
between the pad and rotor to expand, which lifts the pad slightly off the
surface of the rotor and causes several things to happen. The first is that the air reduces the amount
of frictional surface available for stopping the car. Second is that the pad cannot transfer heat as effectively to the
rotor, where it can be dissipated- creating a buildup of heat in the pad and
reducing it’s efficiency.
This gas can be scraped from the surface of the pad by
either slotting or drilling, both of which are outlined below.
First
off, the standard thin disks that come with the TE72 in the front are quite
adequate for many different types of pads.
These are cheap enough that many different sets can be modified to see
what sort of slotting or drilling is most effective enough. The thin disks are small enough such that
they do not keep heat in them, and have enough surface area per volume that
they shed heat relatively easily.
For
an initial upgrade from stock situation, a set of pads with a set of standard
thin disks is a step up in the right direction.
These
are the next progression in the way of things.
Vented rotors have the advantage of having more than twice as much
surface area, allowing for better cooling and less overheating of the pad.
Supplied
standard on the AE86, these can be retrofitted onto the TE72 as a performance
upgrade. The entire strut assembly must
be moved over, but this is necessary for a spring upgrade anyway- and it also
provides an upgrade to twin spot calipers.
FWIW, this is an easy mod which provides a raft of benefits.
The most popular way of removing the built up gas from
the surface of the pad is by drilling holes in the surface of the rotor. There are many advantages in this technique,
as many small holes can be arranged to scrape the pad continuously and also
provide more surface area for heat transfer to occur.
The drawbacks of this technique are that too many holes
destroy the structural integrity of the disk, as well as cause problems with
crack propagation as the brake rotor fatigues.
If you change your rotors every weekend, or inspect and replace often,
then it works out OK. If you wait till
something fails, well, eventually something will. These holes are also excellent places for cracks to start, due to
their inherent heat loading cycles and the physical fatigue properties of a
hole versus an unbroken surface.
If you are going to cross drill your own disks, make sure
you start with brand new ones. This way
they will be easier to drill (not yet work hardened) and you will not be aggravating
current cracks in the material.
When looking for a method to reduce the gas between the
pad and rotor without the drawbacks of drilling, slotting comes to mind. A slot, milled such that the pad is scraped
from inside to outside as the disk rotates, allows for the gas to be removed
without disturbing the structural properties of the disk as badly or creating
such physical stresses on the disk.
Drawbacks to slotting are that you are again reducing the
frictional area of the disk. While
these losses are overcome by the amount of gas removed and the amount of
friction gained, this has to be kept in mind such that the slots milled are
just large enough to do their job- and no more.