WASHINGTON - Mack Trucks is recalling 329 model-year 2011-2012 trucks that are equipped with Gunite automatic slack adjusters, the National Highway Traffic Safety Administration reported. 

Because of incomplete "knitting" of the iron at the time of casting, the slack adjuster housing may lack structural integrity. There's a risk that the housing could break at the handle under normal operating loads, NHTSA said. As a result, slack adjusters with this flow notch could crack under normal braking conditions, leading to potential loss of braking. 

The recall, expected to begin at the beginning of July, affects Mack CHU, CXU, GU, LEU and MRU models. 

To remedy the problem, Mack dealers will replace these slack adjusters free of charge. 

Mack Trucks can be reached at (800) 528-6586.