Navistar (Navistar) is recalling certain model year 2015-2016 International 9900 trucks manufactured January 6, 2014, to March 12, 2015, and 2015-2016 International Lonestar trucks manufactured February 20, 2014, to March 13, 2015. The affected vehicles are equipped with a 6″ diameter stack tail pipe, that may not have sufficient support. The unsupported weight of the upper stack tail pipe and vibration associated with normal vehicle operation over time may cause a crack of the weld joint between the inlet pipe and the flare expansion of the stack tail pipe, which may result in partial or full separation of the stack tail pipe from the vertical exhaust pipe.