Inertia Dynamometer Rotor Crack Test Procedure for Air Disc Brakes


This Recommended Practice applies to commercial vehicles equipped with air disc brakes and above 4536 kg of Gross Vehicle Weight Rating. Other assessments on the friction material or rotor related to wear, durability, correlation to product life, noise, judder, compliance to specific regulations, etc. are not part of this RP (Recommended practice).


Brake rotor cracks on commercial vehicles can compromise the structural integrity of the foundation brake. These failures can amount to significant maintenance and downtime costs. In order to provide an early assessment of this failure mode, vehicle manufacturers as well as brake suppliers have developed multiple laboratory test procedures. These procedures determine (using different test methods and test approaches) the propensity of a given friction couple (brake rotor and friction material) to develop cracks which can render the brakes out-of-service. It is the objective of this Recommended Practice (RP) to establish a uniform and industry-endorsed laboratory method which reflects the most commonly used inertia dynamometer test procedure. This RP harmonizes the test conditions when applicable, and determines the minimum requirements for the test system used to conduct the test. The two methods included on this RP reflect the two main approaches to rotor crack testing. Method A uses a bedding cycle at 200 °C and 300 °C; incorporates performance (torque output) versus pressure during the bedding; Method B uses a single bedding cycle at 150 °C. This RP also presents the method and criteria to assess and report rotor cracks. This RP applies when comparing test results to a baseline, a product specification, or a legacy product design.

  • SAE J 3080
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