System: brakes; hydraulic; master cylinder.vehicle description: school buses built with hydraulic brakes.note: if your vehicle IS presented to an authorized dealer on an agreed upon service date and the remedy IS not provided within a reasonable time and free of charge or the remedy does not correct the defect or noncompliance, please contact am tran service center at 1-800-843-5615. Also, contact the national highway traffic safety adminstration's auto safety hotline at 1-800-424-9393.