The Chevrolet and GMC B series is a series of cowled chassis that were produced by General Motors, primarily fitted with school bus bodies throughout its production. Based on the medium-duty (Class 6-7) trucks produced by the Chevrolet and GMC divisions of General Motors, the B series was produced in three separate generations; GMC initially produced its own version separate from Chevrolet. Introduced in 1966, the B series was redesigned in 1984 and 1992 as a 1993 model.
Following the end of a supply agreement with Blue Bird Corporation, effectively leaving General Motors without a body manufacturer with which to supply chassis, the company exited production of full-size bus chassis, producing the later GMT560 solely as a cutaway-cab vehicle. The Blue Bird Vision entered production in 2004, becoming the first conventional-style school bus produced without a second-party chassis.
As of 2017, General Motors remains a supplier of bus chassis for school bus and commercial bus use. Currently, all examples are cutaway van chassis based on the GMT610 architecture (Chevrolet Express/GMC Savana).
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.
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.
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 the 250 inline-6 (replaced by the 292 inline-6), 366 V8, and 427 V8. In both Chevrolet and GMC school buses, the Allison AT475 3-speed automatic transmission became an option in 1971 with single or two-speed rear axles.
In 1974, the powertrain lineup was modified, as all GMC-built engines were dropped (alongside all diesel engines). In 1980, a diesel engine made its return as Detroit Diesel introduced an 8.2L V8. Dubbed the "Fuel Pincher", it was the first four-stroke engine produced by the company; the engine was available in naturally-aspirated and turbocharged forms.
In 1966, the GMC division moved its school bus chassis from the medium-duty C/K to the all new H6500 heavy truck. A forerunner of both the GMC Brigadier and GMC General, the H-series trucks featured an all-steel front fascia with a center-hinged "butterfly" hood for engine access. Alongside GMC V6 and V8 gasoline engines, GMC school bus chassis were available with Detroit Diesel 6V53 V6 diesels.
In 1969, GMC transitioned its medium-duty trucks to the Chevrolet-based C/K medium-duty chassis introduced in 1967. The heavy-duty GMC school bus chassis remained in use by the division for 1970, before both divisions consolidated designs for 1971.
While General Motors redesigned its entire light and medium-duty C/K truck line for 1973, Chevrolet and GMC retained the previous-generation cowled bus chassis for nearly another decade. For 1984, a second generation was introduced, consolidating conventional trucks and cowled bus chassis for the first time. Codenamed B6, the redesign was again shared by both Chevrolet and GMC, differing only in grille design. From the drivers' compartment, the B6 chassis shared the steering column with its predecessor (with nearly the same instrument panel).
In a major design change, the rear-hinged hood was replaced by a standard front-hinged tilting hood, allowing improved engine access. The 6.0L (366) and 7.0L (427) V8 engines made their return, along with the 8.2L Detroit Diesel "Fuel Pincher" V8. In 1990, the 8.2L engine was discontinued.
In 1985, General Motors developed a modified version of the B series for Ward Body Works as a chassis for the Ward Patriot school bus. To allow for a shortened hood (to improve driver visibility), the front chassis of the C/K conventional was shortened for a configuration similar to that of the smaller Chevrolet/GMC P-chassis. The "semi-forward control" design would be developed further by GM with the Thomas Vista, another bus that would use a GM B-series chassis during its production.
For 1990, General Motors introduced its GMT530 medium-duty truck platform as the Chevrolet Kodiak/GMC TopKick, replacing the previous trucks of that nameplate, the GMC Brigadier, and the medium-duty C/K product lines. B series based on the GMT530 entered production for 1992, as a 93 model year. As with its predecessor, the chassis was shared between Chevrolet and GMC, with only the grille differentiating the two.
The GMT530 B series was powered by a range of gasoline and diesel engines. As gasoline engines were being phased out of school buses during the 1990s, the B series became the last full-size school bus to offer them, with a 6.0L (366 cubic inch) V8 as standard. As the Kodiak/TopKick was renamed the C series in 1997, the 6.0L V8 was eventually phased out in favor of the Vortec 7.4L V8; the 7.4L V8 was replaced by an 8.1L Vortec V8 (one of the largest gasoline engines ever used in a school bus) in 2001. The Caterpillar 3116 was the first diesel engine option, joined by the turbocharged Caterpillar 3126 in 1997. Along with Allison automatic transmissions, the GMT530 B series was available with either 5- or 6-speed manual transmissions.
The last manufacturer to offer a gasoline engine in a conventional-chassis school bus (prior to its reintroduction in 2016 in the Blue Bird Vision), a number of GM gasoline school buses were converted to use alternative fuels, including LPG (propane) and CNG (compressed natural gas). When GM replaced the GMT 530 series of medium duty conventionals with the GMT 560 series in 2003, no direct replacement for the B series was offered. However, the GMT560 would see use for bus builders with cutaway cab buses in many forms, alongside those based on the Freightliner M2 and Ford F-650 Super Duty.
Prior to 1992, the B-series chassis was available to any school bus manufacturer. That year, GM and Blue Bird signed a supply and marketing agreement, with the latter company becoming the exclusive supplier of the then-new GMT530 bus chassis for the next 10 years. The resulting model was named the CV200; while the GM B-7 (internal name for the GMT530-based bus chassis) was standard, Navistar International and Ford (later, Freightliner) chassis were available as options.
Along with the 1991 Navistar acquisition of AmTran, the agreement was a part of a series of mergers and acquisitions in the school bus industry between body manufacturers and chassis suppliers, eventually crippling the market share of General Motors as a chassis supplier as the agreement was not renewed. Effectively shut out of the industry as a full-size chassis supplier, General Motors ended chassis production in 2002 (2003 model) to concentrate on cutaway-chassis buses.
While used nearly exclusively for school bus use, the B-series chassis was adapted for a wide variety of uses by body manufacturers, ranging from bookmobiles to police buses. In the school bus industry, the General Motors chassis was popular for its wide range of engines. During the 1980s and 1990s, its continued use of gasoline engines remained popular, as the powerplants were sometimes used as the basis for conversion to alternative fuels, including LPG (propane) and CNG (compressed natural gas).
Following the chassis and supply agreement between General Motors and Blue Bird in 1992, the B series was bodied exclusively by that company, nearly exclusively as a school bus.
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