Brake Pads & Break-in Procedures

Brake pads wear out as part of their normal operation. Newer vehicles are typically equipped with sensors that notice when pads are becoming thin; the sensors switch on an indicator light in the dash so the driver knows the assembly needs attention. Vehicles without sensors often provide clues in the form of a burning smell on harsh braking; created by the dust brake pads leave on the rotor. As the pads get closer to being worn out, they generate more heat, burning the dust in the process. All four braking assemblies should be checked regularly.

Why Bed In

Brake performance is adversely affected by a poor pad/rotor match. New pads are not matched to the rotors they grip and a break-in procedure, called bedding-in, allows the new combination to function together. If this procedure is not followed strictly to manufacturers instructions, braking performance will likely be severely diminished. Failure to properly bed-in new pads can also lead to a juddering sensation -- often called shimmy -- when braking. Shimmy is very uncomfortable; it transmits through the steering column to the drivers hands and through the suspension to the entire car.

The Importance of Bedding-in

Bedding-in must be done gradually and cautiously. Dave Zeckhausen of Zeckhausen Racing observes, The first few applications of the brakes will result in very little braking power. Gently use the brakes a few times at low speed in order to build up some grip. New pads deposit a microscopic layer of a material called transfer film, which aids in the matching process. Done too aggressively, the process of building up heat to transfer the film can actually cause perfectly good rotors to warp and can also lead to an uneven deposit of the transfer film and the shimmy that is symptomatic. Good bedding-in procedures can also reduce squeal.

Rotors

Rotors wear out comparatively rarely, but they can be scarred by heavily worn pads, and they should be refinished -- or turned -- to make their surfaces as smooth as new when fitting fresh pads. The turning process also removes any trace of transfer film left by the previous pads. The experts at Tire Rack write, Residue from the previous pad compound on the surface or an irregular surface on a used rotor will cause the pads to grip-slip-grip-slip as they pass over the rotor surface under pressure. It is industry practice that pad guarantees are invalidated if rotors are not replaced or resurfaced; the rotors must also be professionally checked to ensure they are free from even microscopic warping.

Bedding-in Procedures

Different manufacturers recommend different procedures specific to their products; observe the instructions provided with your new pads. Do not tow a trailer or have any excess weight aboard while bedding-in. Be aware some degassing occurs from the new pads while bedding-in, so an unusual smell and even some visible smoke is not cause for concern. Typically, the process involves moderate driving for between 300 and 500 miles -- moderate means the avoidance of heavy braking -- and then, in a safe location, deceleration from around 60 mph to around 30 between five and 10 times. Firmly apply then release the brakes during this process, rather than dragging, and wait at least 30 seconds between each application to allow some cooling. The heat generated by braking is exponential; far more is generated when braking from 80 to 60 mph than from 60 down to 40, so observe the directions accurately. Avoid coming to a complete stop; this can leave an imprint of the pad on the rotor that will negatively impact future performance. Some manufacturers recommend making two or three emergency stops from around 45 mph. The vehicle should then be parked, without deploying the parking brake, for as long as it takes for all the brake assemblies to cool completely. Full matching up and optimal performance can be expected within 500 to 1,000 miles of regular driving.