The Chevrolet and GMC B series was a series of cowled chassis that were produced by General Motors. Produced across three generations from 1966 to 2003, the model line was a variant of medium-duty trucks marketed under the Chevrolet and GMC nameplates. Initially derived from the medium-duty C/K series, later examples were derived from the GMT530 architecture. The B-series was constructed as a cowled-chassis design; also known as an incomplete vehicle, all bodywork aft of the firewall was produced by a second-stage manufacturer. While primarily used for school bus applications, General Motors offered the chassis for multiple commercial and specialty uses. Following 2003 production, the B-series was discontinued as GM concentrated on bus production derived from cutaway cabs. Until its 2009 discontinuation, the medium-duty GMT560 chassis was used for bus applications (only in a cutaway configuration). As of current production, General Motors provides bus chassis for both school bus and commercial bus applications, deriving all production from the light-duty GMT610 (Chevrolet Express/GMC Savana) cutaway van. Background Prior to 1966, all medium- and heavy-duty trucks of General Motors were derived heavily from the C/K series trucks (and the Task Force trucks before them). Although using a stronger frame and suspension, much of the bodywork was shared. With the exception of divisionally-produced engines, the Chevrolet and GMC medium-duty trucks were largely identical to one another. Consequently, the conventional-type school bus chassis used for both divisions were largely the same. First generation (1966–1983) For 1966, GMC ended the use of a shared conventional bus chassis as it debuted its own version derived from its H-series heavy truck line; Chevrolet debuted its own design in 1967, derived from the C/K medium-duty line. For 1971, both divisions consolidated conventional bus production solely to the C/K chassis. For 1973, General Motors redesigned the entire C/K truck line, ranging from half-ton pickups to medium-duty trucks. As Chevrolet and GMC had only adopted the C/K chassis together in 1971, GM would continue the production of the 1967-generation chassis for another decade. After 16 years as a Chevrolet and 12 years of production as a GMC, the first-generation C/K bus chassis was retired after 1983. Chevrolet (1967–1983) In 1967, Chevrolet moved the medium-duty C/K to a dedicated chassis, taking the school bus chassis with it. As with the previous generation, the design was a rear-hinged "alligator"-design hood. The division offered its conventional school bus chassis with Chevrolet-produced engines, including