Abstract: The balance bearing hub of a truck cracked at storage time after final assembly. To make sure the mode and causes of the cracking, the chemical component of balance bearing hub was tested. The fracture and microstructure of balance bearing hub were observed and the tensile property and impact property of balance bearing hub were also tested. The results indicate that the cracking mode of balance bearing hub is one-time brittle crack. The excessive addition of nucleating agent at productive process leads to high level of silicon content and large brittleness, which is the main factor of the cracking of balance bearing hub. Therefore we control strictly the addition of nucleating agent to limit the silicon content at balance bearing hub and the impact toughness improves obviously. We solve the brittle crack of balance bearing hub finally.