This study investigates the effect of microstructural variations on the mechanical properties of CuZn35Mn2Al1Fe1-C-GS brass alloy. Specimens taken from positions with different cooling rates in a large cast component exhibit coarse-grained (approximately 5 mm) and fine-grained (approximately 1 mm) microstructures. Fine-grained samples demonstrate at least a 7% increase in Ultimate Tensile Strength (UTS) and up to a 33% higher long crack threshold ΔKth,lc. Hardness measurements are similar between microstructures. The NASGRO model and cyclic R-curve are applied to fit crack propagation data, and fractographic analysis reveals distinct fracture mechanisms. The results indicate that a fine-grained microstructure enhances tensile strength and crack resistance, providing valuable insights for the design and maintenance of heavy machinery components made from cast brass.