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TECHNICAL
INFORMATION
The following technical information will give you a better understanding
of disc brakes and their use as well as essential information
you'll need to make the correct choice of kits and/or components.
In the listings of recommended kits for specific applications,
we have provided basic recommendations for various car applications.
All applications are by no means limited to those shown. If you
have any doubt or questions about your particular application,
engineers are as close as your telephone. Our engineers are highly
qualified and helped "write the book" on disc brakes.
They'll be happy to answer your questions regarding selection
of components or kits and their use.
SELECTION OF
COMPONENTS
ROTORS: Generally, rotors are available
in two main groups -- vented and solid. For lighter cars racing
on dirt, such as midgets, sprinters, etc., we recommend solid
rotors, which offer the performance needed at a lower weight.
As cars get heavier and braking requirements more severe, (such
as on asphalt, etc.), we work up to our thicker, vented rotors.
These offer maximum performance and heat dissipation. For cars
racing in dirt and weighing approximately 1600 -2000 lbs., our
.810" vented rotors work very well. For vehicles weighing
up to 2800 lbs., we recommend our 1.250" vented rotors.
For asphalt racing, our Martinsville vented rotors in either
1.250" or 1.380" thickness are the sure ticket. The
Martinsville vented rotor offers the perfect combination of performance
and light weight.
CALIPERS: If you're using a SIERRA
kit, we have included the caliper for that particular application.
For Special applications, we recommend you consult our engineers.
To determine the proper caliper, they will need to know the following:
vehicle weight, type of racing (oval, drag, road race, etc.),
racing surface (asphalt or dirt), and the driver's tendencies
(i.e. whether or not the driver is exceptionally hard on brakes,
etc.).
BRAKE PADS: We stock a wide range
of pads suitable for all racing needs for each of our calipers.
We've selected pads that are commonly used and readily available
throughout the racing industry. This makes it easy for you to
obtain replacements and spares whenever and wherever you need
them. Softer pads are used where high friction is desirable and
racing conditions are less severe, as on dirt tracks. The harder
pads will withstand higher temperatures, but the friction is
somewhat lower. For a generalized table of brake pad characteristics,
ranging from soft to hard, see the chart.
HATS: To the average brake manufacturer,
hats are nothing more than a means of adapting the rotor to the
hub. We've gone a few steps further. Our hats are not only extremely
light, but they are designed to provide maximum airflow to the
outboard face of the rotor -- normally a dead spot for air flow.
SIERRA hats are available in a wide variety of offsets and bolt
patterns.
MASTER CYLINDERS: Using
two master cylinders, in modern oval track racing and road racing
cars, has become extremely popular. It is the optimum configuration,
providing added safety and the opportunity to adjust the balance
of the system from front to rear. This is very necessary for
precise chassis tuning. As a general rule, we recommend using
a pedal ratio of approximately 5.5:1 for master cylinder bore
size. For pairs of Mini GN single calipers, we recommend the
use of a 3/4" diameter bore master cylinder. For Mini GN
Dual, XL Series, and GN 200 caliper pairs, we recommend 7/8"
diameter bore master cylinders.
PRESSURE GAUGES: It is recommended
that in-dash pressure gauges, or gauges adapted to temporarily
screw-in at the bleed screw be employed in your brake system
so that you can accurately work with the balance bar pedal assembly,
or adjustable proportioning valve, until the pressures are precisely
where you want them. These also provide you with factual data
which will help you set the car up properly each time you return
to a particular track. A chart is routinely kept from past experiences
so that you can be lapping with the ultimate setup while others
are "getting dialed in."
INSTALLATION
ROTOR INSTALLATION AND RUN OUT:
We highly recommend rotor attaching bolts be lock-wired. Rotor
run out should be adjusted upon installation to be less than
0.005". Adjust by shimming between rotor and mounting face
of hat or hub with decreasing thickness shims, from the thickest
point to the point opposite. Run out should be checked periodically,
but can be assumed to be acceptable if no other problems such
as brake drag, pedal oscillation or piston knock-back are encountered.
CALIPER MOUNTING BRACKETS AND
POSITIONING: If caliper mounting brackets are not available
from your chassis manufacturer, they may be fabricated from mild
steel. We recommend 5/16" (minimum) for dual piston calipers.
Be sure that the bracket is sturdy and will not deflect when
the brakes are applied. A weak bracket can cause tapered lining
wear, cocking of the pistons, ejection of the pads, fracturing
of the caliper mounting ears, or bracket failure. Saving a few
ounces on a caliper mounting bracket may not be worth it! The
mounting surface on the caliper mounting ears must be parallel
to the rotor within 0.020", when installed. The caliper
must be centered on the rotor to the extent that new pads can
be easily dropped in when the caliper pistons are fully retracted.
AIR DUCTING: When ducting is
necessary, we recommend at least 3" diameter ducts, directed
to the inside diameter of the rotor. Ducting is usually required
for heavier cars on asphalt, such as late model and modified
cars. In some very severe short tracks, it is not uncommon to
run a second, smaller-diameter duct directly to the caliper.
MASTER CYLINDER: Always
be sure to mount your master cylinder as rigidly and as high
in the car as possible. When running fluid lines, keep them running
downward from the master cylinder. Always make sure that the
master cylinder diaphragm is in place and in good condition.
If you use a remote fluid reservoir, be sure to mount it as high
as you can in the car. CAUTION: Be sure the master cylinder does
not have a residual pressure valve.
 PEDAL
RATIO: Pedal ratio is distance "A" divided by distance
"B." (See illustration at right -- the distance from
the pedal pivot point to the center of the foot pad, divided
by the distance from the pedal pivot point to the master cylinder
actuating rod attachment point.) It is a method of pushing harder
on the master cylinder rod and gaining brake pressure by mechanical
advantage. As the pedal ratio is increased, required pedal pressure
is reduced. Also, keep in mind that the stroke of the pedal will
increase as the pedal ratio is increased. In our application
selections, we've given specific pedal ratios/master cylinder
combinations. If, however, you are uncertain about any other
situation, a good starting point is about 5 to 1, which is average
for automotive purposes.
FLUID: When choosing a brake fluid,
dot standards do not tell the whole story. Choose a fluid based
on its maximum dry boiling point. It should be at least 450 degrees
F. We recommend SIERRA Z-10, 570 degree automotive racing fluid.
Due to the nature of the brake fluid and its tendency to absorb
moisture for the atmosphere (thereby reducing its boiling point),
we suggest you get small cans, which remain sealed until you
need them. This way you can ensure a higher boiling point of
the fluid in your car's system. NOTE: We strongly recommend you
do not use silicone brake fluid with any of our products. We
have tested extensively and found silicone fluid has properties
that may cause seal swelling and may not be appropriate for racing
use.
BLEEDING: If you are serious about
your racing plan to be involved for more than one year, we highly
recommend using a pressure bleeder with a rubber bladder separating
the air side from the fluid side; you'll save yourself a lot
of problems. When using a pressure bleeder, set the pressure
at approximately 30psi, and be sure all of the air is out of
the fluid side. Use hoses from the bleed fittings to a bottle
with fluid in the bottom. Make sure the end of the hose is submerged
in the fluid. This will prevent air being sucked into the system.
Never pump the pedal when bleeding. Pumping will only aerate
the fluid and prevent complete bleeding. Follow this procedure:
- Push and hold down the pedal.
- Open the bleeder valve until the fluid is released.
- Close the valve and release pedal.
- Wait 3-5 seconds and repeat steps 1-3 above. Bleed until
clear, airless fluid is observed.
Have someone watch the fluid level in the reservoir and add fluid
if the level drops to within 1/2" from the bottom of the
reservoir. Complete your bleeding procedure all the way around
the car at least two times. Additional bleeding may be helpful
after running the car for several laps. For the serious racer,
we recommend a quick-bleeding of the system prior to race weekend.
This will replenish the fluid in your system and maintain a high
boiling point.
FREE RUNNING: After all phases
of installation and bleeding, test the free-running condition
of each wheel for correct operation. Any drag is a sign of a
non-standard situation somewhere in the system.
PAD AND ROTOR BREAK-IN: In some
cases, pads require some preliminary break-in to achieve their
maximum friction. Likewise, new rotors may require similar treatment
to prevent premature and excessive wear. New pads should first
be brought up to elevated temperature to a point of experiencing
fade. At that point, the car should be brought back into the
pits and the pads and rotors should be allowed to cool to the
point where the rotors are cool to touch. New rotors should be
broken in more slowly and not overheated on the first application
of lapping.
TUNING AND BALANCE BAR: In most cases,
the front brakes will do the majority of the work. A main concern
is that the front brakes are not over-worked. Therefore, it is
advantageous to make sure that the rear brakes are doing as much
as possible, without causing any handling problems. The simplest
and most effective method we recommend is to keep "dialing
in" more and more rear brake until you reach a point where
it is too much. Then return the adjustment to the point prior
to being too much. On heavily rear-braked cars, simply reverse
this procedure.
USING THE BRAKES: When using
the brakes, use them hard, then release the pedal. A foot on
the pedal, regardless of how light the pressure, will cause the
brakes to drag slightly, robbing them of their normal cool-down
time on the straightaways. It also temporarily locks up the fluid
system and can cause fluid overheating and boiling. Either of
these conditions can result in total brake failure. On some cars,
a stop light switch can be adapted to a small dashboard light
as a reminder.
MAINTENANCE: Prior to each racing
event or weekend, it's a good idea to follow the checklist below
to make sure your car is up to its maximum potential:
- Check for leaks around: calipers, pistons, fittings and lines
- Bleed once around the car to replenish the system with fresh
fluid
- Check air ducting to make sure that it is properly directed
and free from obstructions
- Make sure all four wheels rotate in a drag-free condition
WHEN REPLACING PADS:
The exposed portion of the piston must be cleaned with a suitable
brake cleaner, or brake fluid, before the piston is retracted
into the caliper housing. This will avoid damage to the piston
seals.
WHEN THE CAR IS RACED WEEKLY: We
recommend replacing the seals once at mid-season and rebuilding
between seasons. For lesser-used cars, seal replacement between
seasons or as necessary should be fine.
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MAINTENANCE
AND TROUBLESHOOTING
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BRAKES DRAG
- Bad master cylinder
- Tapered lining wear caused by improper caliper mounting
- Residual pressure valve in system
- System hydraulically locked up from lack of free play in
pedal linkage
- Weak, deflective caliper mounting brackets
- Caliper not mounted square to rotor
- Excessive rotor run out
THE PEDAL GOES TO THE FLOOR DURING A RACE
- Fluid boiling caused by:
- Overheating from brake drag
- Old or inadequate fluid
- Undersize brake system for application
- Master cylinder failure
- Leak in caliper or hydraulic lines
- Pedal linkage failure
- Excessive spindle deflection in cornering causing caliper
piston knock-back
TOO DEEP A PEDAL
- Air trapped in fluid (incomplete bleeding)
- Master cylinder too small
- Pedal ratio too great
- Excessive spindle deflection in cornering causing caliper
piston knock-back
- Rotors warp
- Calipers not mounted square to rotor
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HAVE TO PUSH TOO HARD (CAR WON'T STOP)
- Master cylinder too large on the pedal
- Insufficient pedal ratio
- Inadequate caliper piston area
- Oil or grease on break linings
- Frozen pistons in caliper
- Fade caused by improper brake lining compound for application
OSCILLATION FEED BACK
- Excessive rotor run out in pedal
- Rotor faces not parallel
- Cracked rotor
- Loose or improperly mounted caliper
- Lining build up (welding) on rotors
- Excessive front bearing clearance
CAR PULLS
- Oil or grease on brake lining
- Frozen pistons in caliper or rotor
- Front end alignment
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