Tech Stuff

Diagnosing and correcting brake life and performance issues

Cleanliness is vital for proper pad and rotor break-in and long-term life. Don’t just shoot the rotor with a cleaning solvent. Wash the rotor in a mixture of HOT water and an effective detergent such as Dawn dish washing liquid, scrubbing vigorously with a nylon brush.
<p>Cleanliness is vital for proper pad and rotor break-in and long-term life. Don&rsquo;t just shoot the rotor with a cleaning solvent. Wash the rotor in a mixture of HOT water and an effective detergent such as Dawn dish washing liquid, scrubbing vigorously with a nylon brush.</p>

When a vehicle’s brake pads and/or rotors wear faster than expected, a host of variables need to be considered, including materials, prior installation methods, driver abuse, etc. In this article, we’ll discuss potential issues and offer suggestions for checking and correcting customer concerns regarding brake life and performance.

Pad and rotor break-in

As Rick Kearns, Curriculum Training manager at the Federal-Mogul Technical Education Center in St. Louis noted, break-in is probably the top reason for premature wear. The need for proper break-in has become more important in recent years due to the use of lighter weight materials, rotor metallurgy and pads materials. The two mating surfaces (pad and rotor) need to transfer material (pad to rotor and rotor to pad) in order to seat together properly. Kerns recommends the tried ‘n’ true “30/30/30” method, involving 30 stops, each from zero to 30 mph, with a 30 second cool-down time between each stop.

As the pads mate with the rotor disc surface, and depending on the type of pad formula, a small amount of friction material is transferred to the disc surface, which increases braking efficiency.

Clean, clean and clean!

Proper washing of a brake rotor is all too often ignored. Any brake rotor, new or used, must be thoroughly cleaned prior to installation, in order to remove any and all contaminates.

New rotors are treated to a temporary anti-rust coating to prevent surface corrosion during packing, shipping and storage. This might involve a simple oil or a waxy-type coating. Regardless, this MUST be removed before installing the rotors. The common approach is to spray the disc surfaces with a brake cleaning solvent or a quick wipe-down with a rag and solvent (brake cleaner, lacquer thinner, etc.). While a solvent cleaning is done with good intentions, rotors should be final-washed in HOT water and an effective detergent. My favorite is Dawn dish washing liquid and hot water.

Once cleaned, the rotor should be handled while wearing clean latex gloves. During rotor, caliper and pad installation, do your best to avoid contaminating the rotor disc surfaces. Understandably, this is difficult to avoid, but if/when dirty or greasy fingerprints appear on the surfaces during installation, clean those areas again with a spray-on brake cleaner, preferably followed by a spot-scrubbing with hot soapy water and rinsing. Any contaminants remaining on the disc surfaces will quickly transfer to the pads, reducing the coefficient of friction that would be available if the rotor were properly cleaned at the outset.

In addition to rotor cleanliness, pay attention to the caliper mounting. Make sure that the caliper pins, guideplate and bridge are clean. That means eliminating all rust buildup on the bridge plate. Remove the bridge, wire brush any rust buildup, bead blast it and apply a protective coating (SEM etching primer and urethane paint for example). Rust tends to build up under the guideplate, which can easily affect caliper fit and movement. An example of common caliper hang-up issues involves some GM SUV models equipped with four-wheel disc brakes, where rust tends to build up below the guide plate causing the pads to lock in place and wear prematurely.

On-car brake lathes are preferred for today’s rotors to eliminate variables of tolerance stack-up, and because many newer vehicles’ lightweight rotors are difficult to properly secure in a traditional brake lathe.
<p>On-car brake lathes are preferred for today&rsquo;s rotors to eliminate variables of tolerance stack-up, and because many newer vehicles&rsquo; lightweight rotors are difficult to properly secure in a traditional brake lathe.</p>

Rotor warp

While rotor runout specifications may differ depending on make, model and year of the vehicle, generally speaking any rotor with more than 0.002 – 0.005 inch lateral runout should be either resurfaced or replaced. With the wheel removed, secure the rotor to the hub with at least three fasteners, torqued to 40 ft.-lbs. Mount a dial indicator (anchored rigidly to a non-moving surface) with the indicator gauge probe contacting the rotor disc surface at a 90-degree angle, about one inch from the outer edge. Preload the indicator about 0.050 inch, then zero the gauge. Slowly rotate the rotor and observe the gauge (rotate a full 360 degrees several times). Using a marker, mark the point of highest lateral runout and compare your reading to the manufacturer specification.

Remove the rotor, and clean the mating surfaces on the rotor and hub. Place the dial indicator on the hub itself and perform a runout check, and compare your reading to the factory specification. Check wheel bearing end-play (and replace or adjust as needed).

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