GMC motorhome
Encyclopedia
The GMC motorhome was produced by the GMC Truck & Coach Division of General Motors
for the 1973 through 1978 model years in Pontiac, Michigan
, USA. It was the only complete motorhome
built by a major auto/truck manufacturer producing what GMC hoped would be their halo vehicle. Part of the reason this vehicle is so different from other motor homes of the era is that it was not conceived as just a "camper," but as a vehicle for comfortable travel as well. The design was radical for the day with front-wheel drive and a low profile, fully integrated body. At the time (as now), motorhomes were built by recreational vehicle manufacturers on bare frames and drivetrains supplied by a chassis manufacturer. GMC built the bodies and in most cases the interiors in-house, and designed the chassis and drivetrain to create a motorhome enclosure that could be adapted to a range of purposes. Empty shells were supplied to other RV manufacturers for upfitting the interiors and also to specialty manufacturers for a range of custom purposes ranging from mail delivery and mobile training facilities to people movers and ambulances. It was built in 23 and 26 ft (7 and 7.9 m) lengths.
Another parallel design was the Revcon motorhome, which starting in 1972 was an all-aluminum body front-wheel drive coach, initially with the same Toronado drivetrain as the later GMC. Beginning in 1978, the Revcon took on a more aerodynamic design similar to the just-canceled GMC motorhome, which included a slant nose and dual rear axle, while adopting a Chevy 454 engine and Turbohydramatic 475 transmission. These were in production through 1990, with one coach built in 1991 using remaining components before the factory closed.
The clay full scale 26 feet (7.9 m) motor home was likely the largest clay model GM ever made. 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 prototype fiberglass parts for the first prototype bodies Pictures of the scale models, the sketches and drawings and finally full size clay are most interesting. The evolution from the earliest designs with pronounced fender flares, wrap around rear windows and tail lights and other eye-pleasing shapes, drifted toward a still pleasing, but more "manufacturable at reasonable cost" design in the end.
The motorhome
had a front-wheel-drive transaxle 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. Both used the GM-designated Turbohydramatic 425 automatic transmission, with a wide 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 gal tanks.
The GMC was equipped with front disc brakes and drums on all four rear wheels. A popular owner modification puts disc brakes on a pair, or sometimes all four rear wheels as well. The front-drive configuration eliminated the driveshaft and rear differential and solid axle found on most front-engined motorhomes. As a result, the floor could be designed only about 14 inches (35.6 cm) above the roadway. The low floor was too low for a rear cross axle, and GM designed the rear suspension as a tandem pair of wheels, mounted on bogies which 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 convoluted air bag 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 motorhomes were built in either 23 feet (7 m) or 26 feet (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 (355.6 cm) for the 23 feet (7 m) coach and 160 inches (406.4 cm) for the 26 feet (7.9 m) coach. All GMC motorhomes are 96 inches (243.8 cm) wide and about 9 feet (2.7 m) tall including the usually-installed roof air conditioner. Interior head room is 76 inches (193 cm).
Gross vehicle weight rating for the 23 feet (7 m) coach was 11500 pounds (5,216.3 kg) and 12500 pounds (5,669.9 kg) for the 26 feet (7.9 m) coach. Most GMCs with factory interiors have a 30 gallons (113.6 l) freshwater tank and a 30 gallons (113.6 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. By avoiding materials that can rot in the body skin and frame of the motorhome, the GMCs retain a reputation as being the most restorable and rebuildable of vintage motorhomes. Many formerly abandoned GMCs have been successfully brought back to life because of the durable design.
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. The aerodynamic styling, with the wrap around windshield and expansive glass area, gave the vehicle a futuristic appearance.
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.
GMC motorhomes in good condition and in proper tune are as efficient as similarly powered modern motorhomes, despite the use of computer-controlled engines on the latter, and typically see 9 to 11 miles per US gallon (21 to 26 L/100 km; 11 to 13 mpg-imp) of regular unleaded fuel. GMC Motorhomes tested via a wind tunnel were reported to have a drag coefficient of 0.31, which is typical of modern sedans (although offset by the large frontal area).
A press release datelined Pontiac, Nov. 11, 1977 read as follows: "GMC Truck & Coach Division of General Motors plans to discontinue producing luxury MotorHomes and similar TransMode multi-purpose vehicles and convert those plant facilities to expand truck operations, a GM vice president said today. Robert W. Truxell, general manager of GMC Truck & Coach said, "As a result of this action, GMC will be able to utilize production facilities more effectively for servicing growing truck demands."
William Bryant
The GMC motorhome also enjoys an active online presence, with hundreds of owners participating in an active online forum and with a large number of web pages devoted to information on maintaining and updating the GMC.
Many GMC owners have volunteered to appear on a list that makes them available to other GMC owners who experience mechanical difficulties in their areas. The characteristic mutual support of GMC motorhome owners is a reason cited often by new owners for why they picked a vintage GMC over a new motorhome.
Several companies specialize in parts for GMC motorhomes, and the strong community has developed a substantial cottage industry for needed replacement and modernization parts. Most parts are still available from GMC or aftermarket suppliers who support muscle-car-era Oldsmobiles, or from suppliers dedicated to specialized GMC parts production.
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
for the 1973 through 1978 model years in Pontiac, Michigan
Pontiac, Michigan
Pontiac is a city in the U.S. state of Michigan named after the Ottawa Chief Pontiac, located within the Detroit metropolitan area. As of the 2010 census, the city had a total population of 59,515. It is the county seat of Oakland County...
, USA. It was the only complete motorhome
Motorhome
A motorhome is a type of self-propelled recreational vehicle or RV which offers living accommodation combined with a vehicle engine. The term motorhome is most commonly used in the UK, US, and Canada.-Features:...
built by a major auto/truck manufacturer producing what GMC hoped would be their halo vehicle. Part of the reason this vehicle is so different from other motor homes of the era is that it was not conceived as just a "camper," but as a vehicle for comfortable travel as well. The design was radical for the day with front-wheel drive and a low profile, fully integrated body. At the time (as now), motorhomes were built by recreational vehicle manufacturers on bare frames and drivetrains supplied by a chassis manufacturer. GMC built the bodies and in most cases the interiors in-house, and designed the chassis and drivetrain to create a motorhome enclosure that could be adapted to a range of purposes. Empty shells were supplied to other RV manufacturers for upfitting the interiors and also to specialty manufacturers for a range of custom purposes ranging from mail delivery and mobile training facilities to people movers and ambulances. It was built in 23 and 26 ft (7 and 7.9 m) lengths.
Influences
Prior to the introduction of the GMC motorhome, a handful of other manufacturers made use of a similar front-wheel drives, which went on to inspire the use in the GMC. These included the Cortez from the Clark Equipment Corporation which initially offered a four-speed manual transmission with front-wheel drive, available from 1963 to 1970 until the division was sold to Kent Industries. From 1971 to 1977, a redesigned Cortez-SD was manufactured, initially by Kent and later a group of investors, using the same Oldmobile 455 and three-speed automatic transmission as the GMC motorhome would adopt in 1973.Another parallel design was the Revcon motorhome, which starting in 1972 was an all-aluminum body front-wheel drive coach, initially with the same Toronado drivetrain as the later GMC. Beginning in 1978, the Revcon took on a more aerodynamic design similar to the just-canceled GMC motorhome, which included a slant nose and dual rear axle, while adopting a Chevy 454 engine and Turbohydramatic 475 transmission. These were in production through 1990, with one coach built in 1991 using remaining components before the factory closed.
Design and Specifications
Industry rumors had been circulating for some time that GM was going to be building a motor home. On February 7, 1972 it was made official. About this time the new vehicle was known as the TVS-4, Travel Vehicle Streamlined. The Motor Home 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 feet (7.9 m) motor home was likely the largest clay model GM ever made. 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 prototype fiberglass parts for the first prototype bodies Pictures of the scale models, the sketches and drawings and finally full size clay are most interesting. The evolution from the earliest designs with pronounced fender flares, wrap around rear windows and tail lights and other eye-pleasing shapes, drifted toward a still pleasing, but more "manufacturable at reasonable cost" design in the end.
The motorhome
Motorhome
A motorhome is a type of self-propelled recreational vehicle or RV which offers living accommodation combined with a vehicle engine. The term motorhome is most commonly used in the UK, US, and Canada.-Features:...
had a front-wheel-drive transaxle used in the Oldsmobile Toronado
Oldsmobile Toronado
The original Toronado began as a design painting by Oldsmobile stylist David North in 1962. His design, dubbed the "Flame Red Car," was for a compact sports/personal car never intended for production...
and Cadillac Eldorado
Cadillac Eldorado
The 1953 Eldorado was a special-bodied, low-production convertible . It was the production version of the 1952 El Dorado "Golden Anniversary" concept car, and borrowed bumper bullets from the 1951 GM Le Sabre show car...
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. Both used the GM-designated Turbohydramatic 425 automatic transmission, with a wide 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 gal tanks.
The GMC was equipped with front disc brakes and drums on all four rear wheels. A popular owner modification puts disc brakes on a pair, or sometimes all four rear wheels as well. The front-drive configuration eliminated the driveshaft and rear differential and solid axle found on most front-engined motorhomes. As a result, the floor could be designed only about 14 inches (35.6 cm) above the roadway. The low floor was too low for a rear cross axle, and GM designed the rear suspension as a tandem pair of wheels, mounted on bogies which 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 convoluted air bag 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 motorhomes were built in either 23 feet (7 m) or 26 feet (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 (355.6 cm) for the 23 feet (7 m) coach and 160 inches (406.4 cm) for the 26 feet (7.9 m) coach. All GMC motorhomes are 96 inches (243.8 cm) wide and about 9 feet (2.7 m) tall including the usually-installed roof air conditioner. Interior head room is 76 inches (193 cm).
Gross vehicle weight rating for the 23 feet (7 m) coach was 11500 pounds (5,216.3 kg) and 12500 pounds (5,669.9 kg) for the 26 feet (7.9 m) coach. Most GMCs with factory interiors have a 30 gallons (113.6 l) freshwater tank and a 30 gallons (113.6 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. By avoiding materials that can rot in the body skin and frame of the motorhome, the GMCs retain a reputation as being the most restorable and rebuildable of vintage motorhomes. Many formerly abandoned GMCs have been successfully brought back to life because of the durable design.
They often had luxury features common on upper models of GM brands, such as cruise control
Cruise control
Cruise control is a system that automatically controls the speed of a motor vehicle. The system takes over the throttle of the car to maintain a steady speed as set by the driver.-History:...
, air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
, AM/FM/8-track
8-track cartridge
Stereo 8, commonly known as the eight-track cartridge, eight-track tape, or simply eight-track, is a magnetic tape sound recording technology. It was popular in the United States from the mid-1960s through the late 1970s, but was relatively unknown in many European countries...
sound systems, an aluminum/fiberglass body, as well as air suspension. The aerodynamic styling, with the wrap around windshield and expansive glass area, gave the vehicle a futuristic appearance.
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.
GMC motorhomes in good condition and in proper tune are as efficient as similarly powered modern motorhomes, despite the use of computer-controlled engines on the latter, and typically see 9 to 11 miles per US gallon (21 to 26 L/100 km; 11 to 13 mpg-imp) of regular unleaded fuel. GMC Motorhomes tested via a wind tunnel were reported to have a drag coefficient of 0.31, which is typical of modern sedans (although offset by the large frontal area).
Production
12,921 GMC motorhomes were produced from model years 1973 to 1978. Over 7,000 are currently listed in an international registry. Estimates suggest that at least 8,000 to 9,000 of the original production are still in running condition.A press release datelined Pontiac, Nov. 11, 1977 read as follows: "GMC Truck & Coach Division of General Motors plans to discontinue producing luxury MotorHomes and similar TransMode multi-purpose vehicles and convert those plant facilities to expand truck operations, a GM vice president said today. Robert W. Truxell, general manager of GMC Truck & Coach said, "As a result of this action, GMC will be able to utilize production facilities more effectively for servicing growing truck demands."
William Bryant
Community
The GMC motorhome enjoys one of the most active user groups of any brand of motorhome ever constructed. By a large margin, more GMC owners are members of the Family Motor Coach Association than any other vintage motorhome. The largest club of owners is GMC Motorhomes International, but about 20 other regional clubs are also active. Rallies are conducted frequently, with two GMCMI rallies per year attracting hundreds of GMC motorhomes.The GMC motorhome also enjoys an active online presence, with hundreds of owners participating in an active online forum and with a large number of web pages devoted to information on maintaining and updating the GMC.
Many GMC owners have volunteered to appear on a list that makes them available to other GMC owners who experience mechanical difficulties in their areas. The characteristic mutual support of GMC motorhome owners is a reason cited often by new owners for why they picked a vintage GMC over a new motorhome.
Future
Today the GMC motorhome has withstood the test of time and is being rediscovered by a new generation of recreational vehicle owners. The vehicle was built to allow flexible use of the interior, and thus is ideal for recycling for modern needs. Many are today adding new technologies to the drive train and suspension, satellite electronics, digital audio-video equipment, laminate floors and new design upholstery and appliances to make what has been called the "26-foot, 12,000-pound antique hot rod with plumbing."Several companies specialize in parts for GMC motorhomes, and the strong community has developed a substantial cottage industry for needed replacement and modernization parts. Most parts are still available from GMC or aftermarket suppliers who support muscle-car-era Oldsmobiles, or from suppliers dedicated to specialized GMC parts production.