Off-highway truck rear axle assembly lines traditionally rely on manual processes that expose workers to ergonomic risks due to awkward postures and repetitive high-torque applications. These risks lead to musculoskeletal disorders (MSDs), reduced efficiency, and increased operator fatigue. Addressing these ergonomic challenges is crucial to improving worker safety and optimizing the assembly process. This study identified high ergonomic risks in the lateral control rod and differential carrier assemblies, where multiple operators were involved in manual torque applications. The current research focused on developing a single-operator specialized tool and a universal backup tool to eliminate the need for manual lifting, bending, and backup wrenches, significantly reducing ergonomic risks. The ergonomic interventions resulted in a reduction of REBA scores from 11 to 2 in the lateral control rod assembly and from 6 to 0 in the differential carrier assembly, along with the elimination of one operator in each process. RPN values also dropped from 384 to 8 and from 504 to 18, respectively, indicating improved safety and efficiency. The process optimizations led to a 20% reduction in operator fatigue and cycle time. These findings can be applied across heavy machinery industries, particularly in assembly lines where high-torque applications are prevalent. The improvements benefit both workers and manufacturers by enhancing safety, reducing labor requirements, and increasing productivity.