Pedal travel can be attributed to pad taper, air
or moisture in the brake fluid, boiled brake fluid, caliper deflection,
cocked pads in the calipers, incorrect pedal ratios, and accelerated
pad wear. Use hard brake line as much as possible and keep stainless
flex line to a minimum. Even a stainless flex line, while better
than a rubber hose, will still expand under pressure. Also, check
the hard line, all connections, and piston seals for leaks. Stiffer
calipers can reduce pedal travel. Also, remove tapered pads, as
they will cause the piston to cock and make the pedal feel long.
There are two types of brake fluids, glycol bases
and silicone based. Glycol based is most commonly used in racing
applications. While glycol based fluid does have a tendency to retain
moisture, at high temperatures it is less compressible than other
types of fluids, and thus gives the driver a less spongy pedal.
Racing brake fluids tend to retain moisture if left exposed to air.
The moisture (water) trapped in the fluid bubbles when heated and
forms small air pockets. These pockets are compressible and result
in a spongy brake pedal.
Caliper Deflection and Twist
caliper deflection is the spreading motion of the
caliper as pressure is applied on the pistons. As calipers wear
out the spread tends to increase, thus forcing the pistons to travel
further before the pads engage the rotor to the full extent of the
line pressure. Sometimes caliper twist occurs when the racer is
using very high coefficient racing brake pads, which result in an
increased output of torque and causes the caliper to twist and/or
thrust forward. The twisting effect causes the caliper to deflect
away from the rotor and bend the bridge between the inboard and
outboard sections of the caliper. This increases the pressure on
the calipers and may cause them to bend out of shape; if they are
not reinforced or designed to absorb this constant stress.
Calipers and Pad Shear
caliper shear is when the bolts that hold the caliper
to the mounting brackets fail. This can happen in three ways: 1.
The bolts are defective, 2. The bolts have very low shear strength,
& 3. The caliper is not properly installed.
Pad shear is when the friction material tears away
from the pad backing plate. This is due to a failure of the adhesive
or other retention devise between the pad and backing plate.
The primary role of the master cylinder is to transfer
kinetic energy from your foot to the caliper, via the brake line.
The secondary task of the master cylinder is that of brake line
fluid displacement. If the master cylinder is working well this
displacement is minimal. The master cylinder reservoir stores the
brake fluid, which is transferred to the master cylinder if necessary.
There is a piston in the master cylinder, which is connected to
a rod that is attached to the brake pedal assembly. Applied pressure
on the brake pedal moves the master cylinder piston, which generates
pressure through the bore hole, down the brake line, into the caliper,
causing the brake pads to clamp down on the rotor.
Brake ducting is done to cool the brake system.
The focus of the ducting should be to force heat away from the brake
system. Cool air should be forced in the most direct manner across
or up through the center of the rotor and then away from the brakes
and out of the area. The less bends and turns in the ducting the
better the system. Duct size should be as big as the application
will allow and directed in the shortest and straightest route possible.
If racing on dirt, screens should cover the ducts.
This stands for Root Mean Square, which is the standard
for measuring the finished surface of an object. This is mostly
used in reference to rotors when judging the suitability of their
Bleeding the Brake System
There are numerous methods for bleeding your brake
system. There is the pressure bleeding, manual bleeding, gravity
bleeding, and vacuum bleeding methods. All four have their advantages
and disadvantages. We recommend that you bleed your brakes as often
as possible, never reuse brake fluid, and always replace the fluid
with high temperature brake fluid.
The primary materials for pistons are titanium and
stainless steel. These materials are used as insulators between
the hot brake pads and the brake fluid because of their low thermal
This allows the driver to alter the line pressure
differential between the front and rear brakes. The goal is to balance
your braking system so both front and rear systems reach lock up
simultaneously. The best way to tune your brake bias for pavement
is to start with the front bias. Keep moving the bias to the rear
until the rear brakes lock up, then back off towards the front brakes.
The opposite is used for dirt applications.