GMC B-Series

The GMC B-Series was a class 7, medium duty chassis-cowl produced by General Motors (GM) for the school bus industry. While GM was responsible for only the design, production, and engineering of the truck chassis itself, a variety of body manufacturers were responsible to design, fabricate, and install school bus bodies upon it.

Engineering history

For the vast majority of the B-series' life span, GM's medium duty conventional trucks were based heavily upon the design of their full-sized pickup trucks. While the chassis underneath would be completely different from a typical pickup, a vast majority of the cab and outer body would be carry-over. The B-series, as a result, closely resembled GM's pickup trucks from the 1950s, up until the mid-1960s.

In 1966, while Chevrolet continued to manufacture the B-Series on a medium duty design based upon their full-sized pickups, GMC moved their B-Series truck to the H/J series line. This design of truck would also spawn the GMC Brigadier and Chevrolet Bruin in 1978. The entire front fascia was fabricated out of steel, and featured butterfly-access panels for servicing. This generation of B-Series offered GMC's gasoline V-6, diesel V-6, and gasoline inline-6 engines.

When GMC's medium duty line moved back from the H/J line to a modified variant of their full-sized pickup truck in 1969, so too did the B-Series, albeit in 1971. The only external change to the chassis was a different front clip, which also mandated a different dashboard design. Engine options consisted of the 5.7L, 6.0L, and 7.0L gasoline V8. Later, the Detroit Diesel 8.2L V8 was offered, as well as a turbocharged variant. Transmissions were almost always 4 or 5 speed manuals, although the Allison AT545 4-speed automatic transmission was also offered.

While this series of medium duty trucks were superseded in 1973, the B-series continued to be based upon the previous generation of medium duty conventionals. In fact, this continued to be the case until 1984, when GM finally updated the B-Series to match. Little, if any, change occurred to the powertrain options for this generation.

In 1992, the GMT 530 chassis was adapted to become the next-generation B-Series. This chassis was introduced in 1989 under the GMC TopKick and Chevrolet Kodiak names.

However, in a move that crippled GM's marketshare of the schoolbus market, GM signed an exclusive agreement with BlueBird, Inc. Under the terms of the agreement, Bluebird would be the only body manufacturer allowed to build on the new B-Series chassis, and would also be responsible for all distribution and service. The resulting model was named the CV200, and while the GM B-7 chassis was standard, Navistar-International or Freightliner chassis were optional.

Both gasoline and diesel engines were offered on this generation of B-Series. A 6.0L V8 gasoline engine was offered, allowing potential LPG or CNG conversion. Caterpillar 3116 turbocharged six-cylinder diesels were offered as well. Transmissions were always Allison automatics.

When GM replaced the GMT 530 series of medium duty conventionals with the GMT 560 series in 2003, no replacement for the B-Series was offered. GM has, however, offered cutaway cabs on their Class 4 and Class 5 models, allowing for body builders to add bus bodies in the same manner (and design) as they would on the full-size van cutaways.

While rumours circulate that GM is interested in re-entering the Class 7 bus chassis market, no product has materialized to date.