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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


MAINTENANCE AND TROUBLESHOOTING

INSTALLATION



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:

  1. Push and hold down the pedal.
  2. Open the bleeder valve until the fluid is released.
  3. Close the valve and release pedal.
  4. 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:

  1. Check for leaks around: calipers, pistons, fittings and lines
  2. Bleed once around the car to replenish the system with fresh fluid
  3. Check air ducting to make sure that it is properly directed and free from obstructions
  4. 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.

 

MAINTENANCE AND TROUBLESHOOTING



BRAKES DRAG


  1. Bad master cylinder
  2. Tapered lining wear caused by improper caliper mounting
  3. Residual pressure valve in system
  4. System hydraulically locked up from lack of free play in pedal linkage
  5. Weak, deflective caliper mounting brackets
  6. Caliper not mounted square to rotor
  7. Excessive rotor run out



THE PEDAL GOES TO THE FLOOR DURING A RACE

  1. Fluid boiling caused by:
    1. Overheating from brake drag
    2. Old or inadequate fluid
    3. Undersize brake system for application
  2. Master cylinder failure
  3. Leak in caliper or hydraulic lines
  4. Pedal linkage failure
  5. Excessive spindle deflection in cornering causing caliper piston knock-back



TOO DEEP A PEDAL

  1. Air trapped in fluid (incomplete bleeding)
  2. Master cylinder too small
  3. Pedal ratio too great
  4. Excessive spindle deflection in cornering causing caliper piston knock-back
  5. Rotors warp
  6. Calipers not mounted square to rotor
 



HAVE TO PUSH TOO HARD (CAR WON'T STOP)

  1. Master cylinder too large on the pedal
  2. Insufficient pedal ratio
  3. Inadequate caliper piston area
  4. Oil or grease on break linings
  5. Frozen pistons in caliper
  6. Fade caused by improper brake lining compound for application


OSCILLATION FEED BACK

  1. Excessive rotor run out in pedal
  2. Rotor faces not parallel
  3. Cracked rotor
  4. Loose or improperly mounted caliper
  5. Lining build up (welding) on rotors
  6. Excessive front bearing clearance


CAR PULLS

  1. Oil or grease on brake lining
  2. Frozen pistons in caliper or rotor
  3. Front end alignment






 

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