The SAE J2521 procedure is applicable to high frequency squeal noise occurrences for on-road passenger car and light trucks below 4,540 kg of GVWR. The procedure incorporates high temperature and low temperature test matrixes, but does not fully account for the effects of the environment on brake squeal. Much research is currently underway in this area and can potentially be incorporated in future revisions. For the purposes of this test procedure, squeal is defined as peak noise levels equal to or above 70 dB(A) between 1.25 kHz and 16 kHz for tests using a full suspension corners or full axle assemblies, or between 2 kHz and 16 kHz for brakes not using a full suspension corner. Before using this Recommended Practice for chassis dynamometer testing, review in detail the specifics related to at least (a) instrumentation including in-cabin microphones, (b) threshold levels for noise detection, (c) temperature control priority between front and rear axles, (d) vehicle loading and load distribution, (e) cooling air and environmental conditioning, and (f) detailed nomenclature and labeling of channels and sensors.
The current revision of the SAE J2521 includes updates and changes to (a) accommodate for modern testing technologies, (b) improve the squeal noise evaluation matrixes for disc and drum brakes, (c) bring the document into the new SAE format standard, (d) revise its formatting for clearer test sequences, and (e) improve and harmonize definitions, noise evaluation, test setup and conditions, test inertia calculations, and data analysis with other SAE dynamometer test procedures and recent standards and developments from the EKB/VDA working groups in Europe. Lastly, this revision uses lower final temperatures during the fade sections to better represent vehicle-level testing while offering a more severe fade schedule as optional.