Wednesday, September 28, 2016
Calipers - Tech Tips

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Caliper Pad Wear

As long as your pads are wearing evenly across the pad surface, the pads can be used almost down to the backing plate. Spacer plates may be added behind the pad backing plate as it wears so the caliper pistons will not have to be exposed to the abusive track dirt and grit.

A regular check of the brake pads for excessive wear and taper is necessary to ensure proper disc brake performance.

Caliper Bleed Screws Pointing Up

When bleeding the brakes, make sure the bleed screws on the calipers are pointing straight up so there is no possibility of air bubbles getting trapped. If the calipers are mounted on an angle, you will need to unbolt one ear from the bracket. Pivot the caliper so it points straight up and place a spacer between the pads to prevent the pistons from coming out of the housing.

Weight Reduction

Finding areas to cut weight is becoming increasingly more difficult, so if you are evaluating whether or not to take weight out of your brake system, here is something to keep in mind: A caliper’s size (and weight) is largely affected by the size of the brake pad it needs to hold. If you can go to a smaller brake pad (without running out of pad before you run out of event) then a smaller lighter caliper may be for you. For example, if your pads last about 10 races, consider going to a smaller pad that will require changing a bit more frequently. Remember, if you go to a smaller caliper, you won’t affect stopping performance provided piston sizes stay the same. Also keep in mind that pad wear is heavily dependent on operating temperature, so if you are going to experiment with downsizing, make sure you have adequate cooling.

Caliper Mounting

Brake calipers should be mounted square with rotor to prevent excessive piston knock-back and uneven pad wear. While looking at brake area, have someone apply brakes. Caliper should not move (square itself to rotor): only the pistons and pad should move. If caliper is not parallel with rotor, shims should be used between mounting bracket and caliper ears for proper alignment. Caliper brackets should be strong enough not to deflect under heavy braking. All caliper mounting bolts should be of the highest quality and lockwired for safety.

Caliper Selection and Mounting

Most Wilwood extreme performance calipers are one directional because of the differential piston bore design (one end of the caliper having larger pistons than the other); the caliper must be mounted in a specific position relative to the rotor rotation. All Wilwood Ordering Information calipers are marked with a rotor rotation arrow on them. The caliper should be mounted so that the smaller piston end is closest to the rotor entrance, and the larger piston end toward the rotor exit. The larger piston end provides slightly greater clamping force to compensate for pad taper that can occur under extended severe use applications. An improperly mounted caliper (reverse rotation) will cause increased pad taper and reduce overall braking efficiency.

Note that differential piston bore calipers cannot be used interchangeably from side to side - there is a left hand caliper and a right hand caliper. Also, calipers differ depending on whether the mounting is behind or in front of the spindle - this affects bleed screw position. Make sure to properly analyze these criteria when ordering and mounting or replacing Ordering Information calipers.

Pad Selection

Proper selection of friction pads is a critical part of a high-performance disc brake system. It is important to analyze your vehicle’s braking requirements based upon track demands and driver braking tendencies, then select a pad compound which satisfies these needs. The proper compound for you can be found through a trial and error process, or contact Wilwood’s technical department for recommendations.

Pad Bedding

Begin with a series of light decelerations to gradually build some heat in the brakes. Use an on-and-off the pedal technique by applying the brakes for 3-5 seconds, and then allow them to fully release for a period roughly twice as long as the deceleration cycle. If you use a 5 count during the deceleration interval, use a 10 count during the release to allow the heat to sink into the pads & rotors..

After several cycles of light stops to begin warming the brakes, proceed with a series of medium to firm deceleration stops to continue raising the temperature level in the brakes..

Finish the bedding cycle with a series of 8-10 hard decelerations from 55-65 MPH down to 25 MPH while allowing a proportionate release and heat-sinking interval between each stop. The pads should now be providing positive and consistent response..

If any amount of brake fade is observed during the bed-in cycle, immediately begin the cool down cycle..

Drive at a moderate cruising speed, with the least amount of brake contact possible, until most of the heat has dissipated from the brakes. Avoid sitting stopped with the brake pedal depressed to hold the car in place during this time. Park the vehicle and allow the brakes to cool to ambient air temperature.

Caliper Piston Area

A calipers piston area is calculated by finding the total piston area from one side of the caliper (this is true for a single piston caliper also). The graph provides the piston area for individual piston diameters. Note that differential piston bore calipers will be the total piston area of the different size pistons.

Caliper Piston Area

Caliper Rebuilding

If you race on dirt or drag race on a weekly basis throughout the year, you should disassemble your calipers mid-season and inspect the caliper seals for excessive wear or hardness caused by heat. Asphalt racers generally experience more heat and should do inspections more frequently, especially after racing on a track where high temperatures are reached. NASCAR’s Winston Cup, Busch GN, Craftsman Truck and Road Race teams usually replace caliper seals after each race to ensure proper disc brake performance. Disassembly and replacement of the seals is a simple process and can prevent catastrophic brake failure.

Air Ducting for Short Track Stock Car Racing

Proper air ducting has become critical for effective performance of short track stock car disc brake systems. Short tracks, and most road courses, require specific air duct considerations to maximize the brake systems effectiveness. For complete information on stock car air ducting for short track and road racing.

Wilwood Engineering, Inc
4700 Calle Bolero
Camarillo, CA 93012
Phone: (805) 388-1188
Fax: (805) 388-4938