GMC motorhome

The GMC Motorhome is a recreational vehicle that was manufactured by the GMC Truck & Coach Division of General Motors for model years 1973–1978 in Pontiac, Michigan, USA — as the only complete motorhome built by a major auto/truck manufacturer. Manufactured in 23 and 26 ft (7.0 and 7.9 m) lengths, the design was noted for its front-wheel drive and its low profile, fully integrated body.

In contrast to most motorhomes which were manufactured on drivetrain-equipped frames supplied by a chassis manufacturer; GMC designed, engineered, and built the entire vehicle, and in most cases the interiors, completely in-house. Empty shells were also supplied to other RV manufacturers for interior outfitting and to specialty manufacturers for custom outfitting, ranging from mail delivery and mobile training facilities to people movers and ambulances.

Industry rumors had been circulating for some time that GM was going to build a motorhome. On February 7, 1972, it was made official. About this time the new vehicle was known as the TVS-4, Travel Vehicle Streamlined. The motorhome design continued to evolve in the two main areas of styling and chassis. The Design Center was continuing with both the external and interior designs. There were twelve designers working with sketches and 1/8 scale (A-scale) clay models. Three or four of these 1/8 scale clay models were made, each with unique design characteristics, each refining their shapes closer to the final form. Once these models were completed, evaluated, and approved, full-sized drawings were made using 1/4 inch tape to outline the front, rear and side design. These drawings would guide the designers in the next stage: a full-size clay model.

The clay full scale 26-foot (7.9 m) motorhome was created. Once the shape was completed, the clay surface was "polished" with a sponge and cold water and finished with a silver-blue film of DI-NOC, replicating the painted surface of a vehicle. Upon completion of the full-scale clay, plaster cast segments were made of it. Dimensional drawings were made of this final design for tooling and early fiberglass prototype parts for the first prototype bodies.

The motorhome had a front-wheel-drive transaxle, which GM called Unified Powerplant Package, originally used in the Oldsmobile Toronado and Cadillac Eldorado with an Oldsmobile 455 cu in (7.5 L) V8 from the Toronado, but the later models made use of the 403 cu in (6.6 L) V8. (At the time, the Buick Riviera, which shared most of the same components, and used the same E-body platform, as the Toronado and Eldorado until its 1977 downsizing, was still using the conventional rear-wheel-drive layout.) Both used the GM-designated Turbo-Hydramatic 425 automatic transmission, with a wide roller chain drive to connect the output of the longitudinally oriented engine to the transmission. The final drive was connected directly to the transmission, and power was fed to the front wheels using half-shafts that ran under the front portion of the engine. The engine was fueled with regular gasoline stored in two 25-US-gallon (95 L) tanks.

The GMC was equipped with front disc brakes and drums on all four rear wheels. The front-drive configuration eliminated the driveshaft and rear differential and the solid axle found on most front-engined motorhomes. As a result, the floor could be built with about 14 inches (36 cm) clearance above the roadway. The floor was too low for a rear cross axle, and GM designed the rear suspension as a tandem pair of wheels, mounted on bogies that rode on pins attached to the sides of the low-profile frame. With the exception of the wheel wells, the rear suspension does not intrude into the living space. The rear bogies are suspended using a double-ended reversible sleeve airbag that is pressurized by an automatic leveling system to maintain the designed ride height. The leveling system can also be manually controlled to level the coach at a campsite. The overall chassis design, from the use of an existing GM E platform powertrain and a modified rear suspension, has been considered an early ancestor of the crossover.

The motorhomes were built in either 23-foot (7.0 m) or 26-foot (7.9 m) length, with about 90% of the total production being the latter. The wheelbase from the front wheels to the centerline of the rear tandem pairs is 140 inches (360 cm) for the 23-foot (7.0 m) coach and 160 inches (410 cm) for the 26-foot (7.9 m) coach. All GMC Motorhomes are 96 inches (240 cm) wide and about 9 feet (2.7 m) tall including the usually-installed roof air conditioner. Interior head room is 76 inches (190 cm).

Gross vehicle weight rating for the 23-foot (7.0 m) coach was 10,500 pounds (4,800 kg) and 12,500 pounds (5,700 kg) for the 26-foot (7.9 m) coach. Most GMCs with factory interiors have a 30 US gallons (110 L) freshwater tank and a 30 US gallons (110 L) holding tank.

Body construction consisted of a rigid frame made of welded aluminum extrusions. The body frame was mounted on the chassis steel ladder frame using body isolators. The floor was marine plywood, except where it sloped up at the extremities, where they were plate aluminum. The body panels are fiber-reinforced plastic (fiberglass) below the waistline frame extrusion and at the ends. The upper side body and roof panels between the ends are sheet aluminum. GMCs are notable for their large expanse of windows, which redefined the RV industry at the time. They often had luxury features common on upper models of GM brands, such as cruise control, air conditioning, AM/FM/8-track sound systems, an aluminum/fiberglass body, as well as air suspension.

Rear lower compartments provide space for generators and propane tanks. GMCs were optionally supplied with generators from Onan in 4,000 Watts and 6,000 Watts, many of which are still in service. There were no driver's or passenger's doors at the front of the vehicle. A single door amidships on the right-hand side provided access to the main passenger compartment. At the back of the vehicle, the entire rear body panel could be removed by loosening the bolts around its edges. This allowed beds, appliances, and other bulky items to be installed or removed.