In Part I of this story, we covered the origins of GMC through 1956. Part II picks up the story from there.--Ed.

In 1957, GMC's light trucks got a mild restyle and larger, more powerful V-8 engines, and some became the company's first factory 4x4 light trucks. Meanwhile, GM's Detroit Diesel division launched a new "Super E" turbodiesel engine series, with four valves per cylinder for more power and fuel efficiency, according to historian (and former GMC engineer) Donald Meyer.

In the next year, light- and medium-duty models got quad headlamps, a first for trucks, and a new Allison Torqmatic six-speed automatic became available for medium-duty models. The big news for 1959 was a new aluminum-cab semi-tractor with front and rear air suspensions, which was lighter and could haul more payload than conventional competitors.

Modernization and Regulation

Most models were totally restyled for 1960 with cabs designed by Chevrolet, smoother-riding independent front suspensions with torsion-bar springs (instead of I-beams and leaf springs) on 4x2 light- and medium-duty models, an all-new family of GMC 60-degree (150-205-hp) V-6 gas engines, and a 275-hp, 702-cid V-12 that replaced the old GMC L-6s and passenger-car V-8s. The next year brought a more powerful 165-hp, 305-cid gas V-6 and a new 290-hp diesel, while a mild front restyle, a new instrument panel, and available up-level trim arrived for 1962.

For 1963, coil springs replaced the torsion bars in IFS 4x2 light-duty models, while medium-duties returned to front I-beams with leaf springs. Rear suspensions on 4x2 light trucks also reverted to leaf springs, but 4x4s retained coils front and rear. Chevrolet L-6 engines became standard on 1000, 1500, and 2500 models, P1000 deliveries got a 90-hp, 154-cid (Chevrolet) L-4, and Chevrolet two-speed Pow-R-Flow automatics replaced Hydra-Matic four-speeds after the Hydra-Matic manufacturing plant burned down.

As the U.S. became involved in a war in Vietnam in 1964, a G1000 Handivan light commercial van, powered by the standard 154-cid L-4 or optional 120-hp, 194-cid L-6, was introduced, and a Handibus passenger version was added for 1965. The next year brought more powerful 250-cid (Chevrolet) L-6 and optional GMC 351-cid V-6 engines, plus a new optional Hydra-Matic three-speed automatic.

For 1967, a year ahead of federal safety regulations, restyled 1500, 2500, and 3500 C/K models offered energy-absorbing steering columns and instrument panels, a dual-brake system, and standard seatbelts. GMC light trucks began being built alongside their Chevrolet counterparts in the same plants, and in 1968 GMC, now third in U.S. truck sales, took over design and manufacture of all Chevy medium- and heavy-duty trucks. Available engines were 230-, 250- and 292-cid Chevy L-6s and 307-, 327-, and 396-cid V-8s rated from 140 to 310 hp.

New medium- and heavy-duty models were introduced for 1969, including an all-new series of Astro 9500 aluminum tilt-cab semi-tractors with more rounded corners to reduce aerodynamic drag, plus they offered much-improved interior room and comfort. A new wraparound instrument panel, a center console, suspended driver's seats, and available up-level trim made these GMC's most luxurious HD trucks ever. Detroit Diesel power ranged from 230 to 335 hp.

The K15 Jimmy sport/utility arrived for 1970, and new, larger, more powerful Vandura and Rallywagon G vans replaced the Handivan and Handibus as GMC began construction of a new medium-duty truck assembly plant on Opdyke Road in Pontiac. Chevrolet 250- and 292-cid L-6s and 307-, 350-, and 396-cid V-8s powered GMC light trucks, while Cummins diesels were added to HD models as Chevrolet began marketing rebadged GMC HD trucks.

A midsize, car-based Sprint pickup arrived in GMC showrooms for 1971, and front disc brakes replaced drums on most light trucks. Power and torque ratings changed from (engine-only on an engine dynamometer) "gross" to (as installed) SAE "net," and a new Easimatic Hydra-Matic three-speed offered lower-cost automatic shifting to lower-end medium-duty models.

In 1972, medium-duty production moved to the new Opdyke Road plant, and new Allison four- and five-speed automatic transmissions became available in medium-duty and 7500-Series trucks. The following year brought all-new light-duty models (with Chevrolet bodies) offering four trim levels in larger interiors and five emissions-controlled Chevrolet engines ranging from a 250-cid L-6 to a 454 big-block V-8.

Fuel Shortages and More Regulation

All GMC-built gas and diesel engines were discontinued at the end of the 1973 model run, the former replaced by Chevy gas engines in medium-duty models, while no diesels were offered for 1974. Light-truck sales were hurt by the 1973-1974 Arab oil embargo and the resulting fuel shortage as catalytic converters were required to meet emissions standards on 1975 trucks rated up to 6000-pound GVWR. A GMC-patented Dragfoiler rooftop airfoil was offered on Astro cabs to improve fuel economy by reducing aero drag. A new federal safety standard mandated maximum stopping distances for air-braked trucks, but the truck industry and its suppliers struggled to comply with expensive (and underdeveloped) anti-lock systems.

In 1976, GMC began using Caterpillar diesels in medium-duty trucks. In 1978, a new car-based Caballero pickup replaced the Sprint, GMC's futuristic front-drive motorhome was discontinued after six years and 12,921 units, and C1500 pickups became available with an Oldsmobile 350-cid V-8 diesel -- an unfortunate gas-engine conversion that was rough-running, underpowered, and ultimately unreliable. The good news was that NHTSA's unrealistic air-brake performance requirement was shot down by the U.S. Supreme Court because the anti-lock systems needed to meet them were too expensive and unreliable.

For 1979, an SS Special Series upscale exterior/interior package was introduced for Astro semi-tractors that also included a larger grille, which became standard the following year. GMC also built 35 battery-powered electric vans for an AT&T field test, its first electrics since 1916, as a second fuel shortage reduced truck sales.

Worldwide Truck and Bus

Another recession damaged sales in 1980 as Detroit Diesel "Fuel Pincher" V-8 engines, both naturally aspirated and turbocharged, became available in 6000 and 7000 medium-duty conventional-cab trucks. Full-size pickups and SUVs were mildly restyled, and a new series of raised-height medium-duty TopKick trucks was added for 1981. At midyear, the GM Truck and Bus Group was formed with worldwide responsibility for design, manufacturing, sales, and service of all GM trucks and buses. In addition to GM Truck & Bus Vehicle Operations, it included Detroit Diesel Allison Division and GM's Bedford Commercial Vehicle Division in the U.K.

In 1982, GMC Truck & Coach, Chevrolet and GM Assembly Division were merged into Truck and Bus Operations, and Chevrolet Truck Engineering was absorbed into GMC Engineering. A compact S-15 pickup was launched with four engine choices: a 1.9-liter Isuzu four-cylinder, a 2.5-liter Pontiac L-4, a Chevy 2.8-liter V-6, and a 2.2-liter Isuzu diesel L-4, and Chevrolet-built 6.2-liter diesel V-8s became available in full-size light trucks. Truck sales began to recover as 87 percent of GMC's light trucks were purchased for personal use.

The next year brought an S-15 compact utility with available Insta-Trac shift-on-the-fly 4WD. At the other end of the line, a drag-reducing Aero package was offered for Astro tractors that included a collapsible cab-top "Drag-foiler," filler panels between the cab and trailer and an air dam under the front bumper. For 1984, a new Isuzu-built "Forward" series of medium-duty tilt-cab trucks powered by a 165-hp L-6 turbodiesel was introduced. A midsize Safari van was added in cargo and passenger versions for 1985 as GMC light-truck sales set a record.

Robert C. Stempel, the highly respected engineer who would later become GM CEO, was named executive vice president over the Truck and Bus Group in 1986, and Volvo GM Heavy Truck Corp. was formed as a joint venture between GM and Sweden's Volvo. That November, Truck & Bus announced it would close three U.S. plants and begin phasing out bus and Class 8 heavy-duty truck production. The next year, GMC Truck and Coach Operations was renamed the GMC Truck Division (of GM's Truck and Bus Group) with responsibility for sales, service, and marketing of GMC light- and medium-duty trucks. Detroit Diesel Allison's engine operations were sold to Roger Penske to become the Detroit Diesel Engine Corp., production of Class 8 tractors was dropped, and C/K pickups and SUVs were redesignated "R/V" models.