Mack Trucks, Inc. is recalling certain model year 2013-2014 CHU, CXU, GU, MRU, and LEU trucks manufactured July 16, 2012, through march 18, 2013 and equipped with drum brakes. The clevis pin for the brake slack adjuster may be missing a cotter pin. If the cotter pin is not installed, the clevis pin may loosen and fall out causing a loss of brake function on the affected wheel.