A modular crankshaft configured for use within a power end assembly. The modular crankshaft is configured to interconnect a drive shaft and a plurality of linear drive assemblies. The various embodiments of modular crankshafts disclosed herein are assembled by interconnecting a plurality of individual main bearing journals using a plurality of fasteners. One or more embodiments of modular crankshafts may also include individual connecting rod journals that are attached to individual main bearing journals using a plurality of fasteners.