Drilling represents the initial and most crucial phase in open pit mining operations that utilize the drilling and blasting method. The mobility of all drilling machineries, facilitated by the undercarriage moving between drilling sites, is essential. Any malfunction in this system can hinder movement and, ultimately, halt drilling activities. The reliability, maintainability, and availability of such equipment are vital for continuous production and pose significant challenges for mining companies aiming to enhance system utilization. This research focuses on evaluating the reliability, maintainability, and availability of rotary drilling machines’ transmission systems through a case study conducted in Iran. The study involved collecting failure data from four different drilling machines and proposing preventive maintenance schedules for each. The findings reveal that the transmission system’s reliability significantly decreases to zero after 1000–3500 hours of operation. From a maintainability perspective, most machine failures were repaired within 10–45 hours. The study underscores the importance of enhancing the transmission system’s maintainability to boost the overall reliability of drilling operations in mining environments.