EMD used the same basic truck design for SD7 through SD40, termed the Flexicoil. There are many variations on brake rigging (e.g., single-shoe vs. double-shoe, number of brake cylinders) and where things attached (speed recorder sending unit, handbrake) but the basic casting and design is the same -- same centerplate, same traction-motor blower duct locations, etc. The Flexicoil was replaced with the HT-C truck with the Dash-2 introduction. The HT-C provided better adhesion (less weight transfer) than the Flexicoil. The Flexicoil continued to be specified on some post-SD40 models, e.g., Conrail SD40-2s, and was manufactured for some export models into the late 1970s.
S. Hadid