Wilwood Brakes - Dem's Da Brakes Part 2

Rotors And Calipers-There's More To Them Than Meets The Eye.

Mike Harrington Aug 1, 2008 0 Comment(s)
Sucp_0808_01_z Wilwood_brakes Caliper_rack 1/9

We went to the CPP showroom and saw several types of floating calipers ranging from large, single, to dual piston, and of course, let's not forget the array of colors.

In the exciting May 2008 issue of Super Chevy magazine, we left off covering the fundamentals of braking and brake systems. As we mentioned, hydraulic drum brakes have been in use in most OE vehicles since the early 1930s. It wasn't until the 1950s and 1960s that the American OE manufacturers started offering disc brakes on their vehicles.

Disc brakes are commonly compared to a 10-speed bicycle's brakes. Pulling on a bike's brake handle is comparable to applying force to a vehicle's brake pedal. The pads on a 10-speed bicycle clamp down on the spinning wheel's rim and slow the bicycle down through the use of friction. Of course, a 25-pound bicycle and a 3,000-plus-pound car are very different, but the theory is still the same. Kinetic energy is transformed into thermal energy via friction. All vehicle braking systems work in this manner.

Welcome To The World Of Brake CalipersChoosing the right brake caliper for your needs can seem a bit confusing given the fact there are so many different types available to the average hot rodder. No matter the choice, all calipers are designed to function the same way: They convert the hydraulic pressure from the master cylinder into a mechanical clamping force.

Sucp_0808_03_z Wilwood_brakes Eight_piston_caliper 2/9

Some fixed-brake calipers can employ a radical amount of pistons, such as this Stainless Steel Brakes Company eight-piston caliper. (Photo courtesy of SSBC)

A floating caliper system is by far the most typical disc brake caliper found on vehicles. A floating caliper is usually equipped with one or two hydraulic pistons that apply pressure to the pad. The pistons are found on the caliper's inboard side, while the outboard side floats axially on a sliding bracket in relation to the rotor's position. When pressure is applied, the inboard pistons push the brake pad against the disc while the outboard pad clamps against the outside of the rotor.

If the intended vehicle is going to stay a street-driven vehicle, a floating caliper system would be a great upgrade. A floating caliper system is a more cost-effective route (due to its weight, size, and manufacturing costs) when considering a brake system upgrade. For vehicle owners who split their driving time between the track and the street or just for bragging rights, a rigid fixed-caliper system is the preferred choice. Either route-fixed or floating-will stop a vehicle equally well.

Sucp_0808_04_z Wilwood_brakes Wilwood_rotor_piston 3/9

A two-piece Wilwood rotor and six-piston fixed caliper.

Fixed brake calipers are easily identifiable from that of a floating caliper due to their size and unique shape. A fixed caliper is mounted to a rigid bracket that attaches directly to the spindle. A fixed caliper also houses the pistons on opposing sides of the caliper. Typically, pistons on fixed calipers will vary in size from the front to the back, such as 1.00 inch, 1.15 inch, and 1.30 inch. The reasoning behind this is based on pad wear. The smaller 1.00-inch piston is the leading piston (the point where the rotor enters the caliper), followed by the succeeding sized pistons. Theoretically, longitudinal pad wear (a subject we have no time or space to explore in this article) or tapered pads are the reason for the staggered piston sizes.

Fixed calipers are made of an aluminum alloy just like most floating calipers, but are constructed in two different ways: two-piece forged or one-piece billet blocks. Due to their construction, one-piece billet calipers run higher in production costs. Despite the costs, there is no denying the performance benefits of a fixed caliper on a road course.

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One benefit of a fixed caliper system is the ease of changing brake pads while out at the track. Most pads can be changed without removing the caliper.

Rotors: Round And Round They GoRotors come large and small, one piece and two piece, drilled, slotted (or both), and vented. What an array of choices. The American psyche is fixated on size and volume. Nothing looks quite so cool on musclecars as an open five-spoke wheel with large-diameter rotors filling the open space. Bigger is always better, right? Obviously, the answer is going to be yes and no, with subtle shades of gray in between. When upgrading rotor or wheel size, rotational inertia and static weight are two things to take into consideration. The larger the rotor, the more surface area for the pads to grab. And more surface area equals lower heat buildup and better heat dissipation.

Whether rotors are one piece or two piece, they can still be thought of as a two-component part. One is the friction disc, which performs all the actual work, and the second is the rotor hat, which joins the friction disc to the wheel hub and spindle. So why are there two-piece and one-piece rotors? Primarily, the reason is weight savings. The advantage of a two-piece rotor is weight savings out on the track. The hats on the two-piece rotors are usually made of an aluminum alloy, while the one-piece rotors are made of the same metal as the friction disc-gray iron. One-piece rotors will generally cost less than a two-piece and can yield the same results. Iron versus aluminum hats-you decide.

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Shown is a set of GM factory disc brakes. The front disc comes vented, and the unvented rear disc contains the parking brake within the hub. Simple and effective, yes-a great way to stop the car in a grocery store parking lot-but for performance and racing, no. They leave a lot to be desired.

Another rotor feature that immediately catches the eye are drilled and slotted rotors. These rotors don't even have to be moving to look mean and aggressive, but what is their true function? When it comes to modern brake systems, they don't make the vehicle stop shorter or cool off the rotors much faster. Is there a use besides looking cool? Back when brake pads used asbestos, they would generate gases and dust during braking. These gases had no avenue of escape, so they would reside between the brake pad and the rotor, causing a spongy feel to the pedal, otherwise know as brake fade. Cross-drilling the rotors gave these gases an escape route.

Today's brake pad formulas create very little gas, making cross-drilling unnecessary. Cross-drilling does have some advantages as well as disadvantages. Cross-drilling a rotor can add a bit more bite to the rotor's surface, which will essentially shave the brake pad's surface, exposing new material. Of course, this can result in reduced pad life. Another slight advantage is possible cooling by bringing more air into the vanes. But cross-drilling can create thermal stress risers, which can speed up rotor cracking.

On the other hand, slotted rotors have slight advantages over cross-drilled rotors. Should a brake pad become glazed, slotted rotors will help shave away the glazed particles and re-expose the pad surface at a slower rate than cross-drilling. Slotting creates a leading edge on the rotor surface, which helps carry away the minute amount of gases that build up between the pad and rotor surface as well as carry away any dust particles that contaminate the rotor's surface. Slotting doesn't have as much of an adverse affect on the rotor as does cross-drilling, just as in cross-drilling there is an increase in pad wear and brake dust accumulating on the wheels. The advantage is more bite for the pads. The choice is yours-reduced pad wear or better-biting pads.

Super Chevy magazine would like to acknowledge help from a few different sources in writing this article: Danny Nix of CPP, Mike Jonas of SSBC, Carl Bush of Wilwood, Ralph Lisena of ECI, and Rich Nossell of Master Power. These companies helped us with tech info and shed some light on braking technology.

Sources

Wilwood Engineering
Camarillo, CA 93012
805-388-1188
www.wilwood.com
Master Power Brakes
Mooresville, NC 28117
888-351-8785
http://www.mpbrakes.com
Baer Brakes
Phoenix, AZ
602-233-1411
www.baer.com
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