<p>Angular contact ball bearings (ACBBs) are supporting components in motorized spindles (MSs), and their condition directly affects the vibration characteristics and stability of the spindle system. However, existing research on MS dynamics is primarily based on healthy-bearing models, thereby overlooking the effects of bearing defects on system dynamic characteristics. To address this limitation, this study establishes a fault dynamic model of an MS system incorporating raceway defects in ACBBs and elucidates the influence of bearing condition on spindle vibration characteristics. A dynamic model of the housing–bearing–spindle–tool system is established using the Timoshenko beam element formulation. Defect-induced nonlinearities are coupled into the global model via nonlinear bearing support forces, enabling accurate representation of complex nonlinear dynamic behavior. A dynamic model of ACBBs with raceway defects is further developed based on Hertz contact theory. A sinusoidal displacement excitation is introduced to simulate the time-varying defect interactions, enabling systematic characterization of bearing life cycle vibration evolution from the healthy state through early fault to severe damage. The proposed model is validated using a self-developed MS experimental platform under varying operating conditions. The effects of raceway defects on MS dynamics and vibration characteristics are systematically investigated, and the mechanisms of defect-induced vibration are elucidated, providing theoretical guidance and experimental support for structural optimization and health management of MSs.</p>