GMC

History

A Brief History of the GMC Motorhome

Genesis of a Design

In the heady days after the United States landed a man on the moon, General Motor engineers set out to design the ultimate traveling machine. Drawing on the excitement of the times, this vehicle had to exemplify the cutting edge of vehicle design and construction. This was not to be just another recreational vehicle. The common design of the times for RV’s was a boxy, ungainly, top-heavy vehicle on a truck chassis. The GM vehicle was to be innovative in every way. Design work began in 1970, with release planned for the 1973 model year.

The design would draw heavily on General Motors expertise in several areas. First, it was to be front wheel drive. A still rare concept in car design, much less motorhomes. The drive train and front suspension would be the same design that had been used successfully in the Oldsmobile Toronado since 1966; the 455 cubic inch Oldsmobile engine mated to a Turbohydramatic 425 transmission with torsion bar suspension. The rear suspension would draw on GM’s leadership in bus design, using dual swing arms(one leading and one trailing) with a single air spring on each side. Automatic controls would be integrated into the suspension to allow the vehicle to compensate for changes in loading and maintaining a level driving condition at all times. The chassis was to be a steel ladder design. The body framing was to be aluminum and the body exterior was to be a combination of heavy gauge aluminum and molded glass fiber reinforced plastic as had been used in the Chevrolet Corvette.

The use of front wheel drive and the independent swing arm rear suspension brought many advantages to this design. The lack of drive shafts and axles passing under the coach allowed a very low floor height compared to other motorhomes. The low floor height also allowed a low overall height and low center of gravity for the coach. This gave the vehicle almost car-like driving qualities.

Traveling Machine

The emphasis for the design was to be on the traveling experience, not extended “in-the-woods” camping. This resulted in the exterior of the vehicle being dominated by large expanses of glass. Visibility from the driver’s seat is panoramic to say the least. The vehicle was to be manufactured in 23 foot and 26 foot models; fairly short for a motorhome. There were no permanent sleeping areas(at least in the original design). All beds were converted from seating areas when needed. Since the floor plan is fairly compact, care was taken in the design of the beds so they did not encroach on aisle space when opened.

To allow hot water to be available while traveling, marine water heaters were used which incorporated engine coolant loops(this can present a scalding hazard as coolant temperatures generally exceed 200 deg. F). Power for the refrigerator was 12 volts DC and the “house” battery(in the original design)was a standard automobile wet cell; adequate only for overnight use without recharging.

Production Life

After rumors circulated throughout the auto and recreational vehicle industries for nearly two years, the prototype was displayed in May, 1972 at the Transpro ’72 trade show in Washington, D.C. Production vehicles debuted in the 1973 model year to general acclaim from the recreational vehicle community. Two models were offered, Model 230(23 feet) and Model 260(26 feet), in two variations Motorhome(provided with GM finished interior) and Transmode(bare coaches sold to RV manufacturers such as Avion and Coachman who provided their own interior).

Although the design was refined along the way, the basic vehicle was never altered. Body panels from a 1973 will fit a 1978. The most notable change came in 1977, when Oldsmobile dropped the 455 cubic inch engine for the 403. By then, the oil embargoes and energy crises of the 70’s had taken their toll. “Gas guzzler” vehicles like motorhomes fell out of favor and the entire RV industry fell on hard times. The motorhome was never a high volume vehicle and was rumored never to have been profitable for the automotive giant. General Motors decided that the production facilities would be better utilized in the production of light trucks – estimating they could produce 100 light trucks for every motorhome manufactured. The formal announcement came in November of 1977 and production was discontinued in the 1978 model year after manufacturing around 13,000 total units.

A Classic Endures

Almost immediately, this timeless design attracted a fanatical following. Regional and national owners’ organizations sprang up to support the vehicle. Owners wanted to modify their vehicles to make them more amenable to long term camping, and to overcome some of the “compromises” made by GM’s purchasing department in their efforts to reduce costs. These club publications were often the only source of information available. As interest in the coaches continued to grow, a cottage industry sprang up around them. Small manufacturers and garages began to specialize in providing products and services for the vehicles.

The major turning point came in 1992, as General Motors prepared to scrap all tooling and remaining parts inventory. Cinnabar Engineering purchased all the motorhome property from GM and negotiated a license to provide OEM parts for the vehicles. This assured availability of quality parts for the foreseeable future. Also in 1992, GMC Motorhome Marketplace, a monthly magazine which has achieved international distribution, was introduced providing a major source of information and advertising, both commercial and classified, for the GMC motorhome owner. In 1994, Cinnabar began publishing their own quarterly newsletter, GMC Motorhome News, which details proper service, modifications and parts availability.

As testimony to the enduring nature of the design, it is estimated that, of the 13,000 units manufactured, it’s estimated that 8,000 to 9,000 are still in current registration.

Manufacturer Information

The GMC Motorhome was manufactured by the GM Truck & Coach Division 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 motorhomes manufactured on drivetrain equipped frames supplied by a chassis manufacturer, GMC built the bodies, and in most cases, the interiors in-house and designed the chassis and drivetrain as well. Empty shells were 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. Cadillac employed the 501 cu in (8.2 l) engine. 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.

GMC Motorhome chassis

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 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 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 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.

GMC Motorhome production body-drop

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 taken off by loosening a series of bolts around its edges, allowing beds, appliances and other bulky items to be installed or removed.

Production

A total of 12,921 GMC Motorhomes were produced from model years 1973 to 1978. The interior of the motor home was constructed at the Gemini Corporation plant in Mt. Clemens, Michigan. Peter R. Fink, owner of Travco motor homes, was the CEO of Gemini.^[1] The Gemini operation featured a progressive team concept with teams of workers constructing rooms of the motor homes in full, rather than performing repetitive tasks on an assembly line. Beginning operation in 1972, the plant featured state-of-the-art equipment including one of the first programmable routers. Gemini closed a few years after General Motors discontinued production of its motor homes.^[2] 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, November 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.”^[3] Another factor is that the driveline for the new for 1979 E platform which was in the process of being downsized was lighter duty and incompatible with the GVW of the GMC motorhome where the existing Oldsmobile-sourced driveline was being phased out of production (the 403 and THM425 transaxle were phased out and replaced with the Oldsmobile 350 and THM325 when the downsized E platform was under development).

Prior to the introduction of the GMC Motor home, a handful of other manufacturers made use of a similar front-wheel drive configuration and inspired the GMC configuration.^[4] These included the Cortez Motor Home 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.^[5] From 1972 to 1977, a redesigned Cortez-SD was manufactured, initially by Kent and later a group of investors, using the same Oldsmobile 455 and three-speed automatic transmission that the GMC motorhome adopted in 1973.

Another parallel design was the Revcon motor home, which, starting in 1971, was an all-aluminum body front-wheel drive coach, initially with the same Toronado drive train as the later GMC.^[6] Beginning in 1978, the Revcon took on a more aerodynamic design similar to the just-canceled GMC Motor home, which included a slant nose and dual rear axle, while adopting a Chevrolet 454 engine and Turbo-Hydramatic 475 transmission. These were in production through 1990, with one coach built in 1991 using remaining components before the factory closed.^[7]

Years built

1973-1978

Models

Model 260(26 feet long)

Model 230(23 feet long)

VIN Decoding Example TZE167V102359

T Manufactured by General Motors

Z 3 Axle Motorhome

E Gasoline Engine

1 Interior Code

“1” – GM Interior from 1975 to 1978

“0” – GM Interior from 1973 to 1974

“2” – Twin Bed Interior from 1976 to 1977

“3” – Transmode(sold without interior or windows)

6 Model

“6” – Model 260(26 feet long)

“3” – Model 230(23 feet long)

7 Model Year(1977)

V Manufacturing Plant Code

“V” – Pontiac, Michigan

1 First Digit of Production Series Number

All production started with “1”

0 Since total production was less than 13,000, all GMC Motorhomes had a zero in this position

2359 Production sequence number

Interiors

GMC had some notable interior designs in 1975. This was the only year that Avion Coach Travel Trailer Division designed a custom interior for the GMC coach.

Service Parts Identification Label

If the motorhome was furnished with a GMC interior, this label in the glovebox identifies the interior finish model.

641 Kingsley
681 Glenbrook
683 Edgemont
685 Coca Cola
690 Sequoia
692 Painted Desert
693 Glacier
695Canyon Lands
696 Eleganza I
698 Palm Beach

Unique features/Options

The GMC is the muscle car of the RV world. It holds the land speed record for motorhomes, clocking 106mph at Bonneville last year. It’s been immortalized several times as a Hot Wheels toy.

It’s even had a movie career, starring in the 1981 Bill Murray comedy Stripes. But for those of you who grew up in the 70s, the GMC will always be known as Captain America’s van.

That’s pretty remarkable for an RV that only had a six-year production run. But there are many, many remarkable things about the GMC. For starters, it was the first RV created and built by an automaker—and to this day, no other automaker has taken that risk.

GM called the project TVS-4 (‘Travel Vehicle Streamlined, model 4’). For maximum grunt, it dropped in a mighty 455ci V8—the engine that powered the 1966 Toronado. A claimed 260 horses were fed through a three-speed gearbox to the front wheels; with no driveshaft running to the back axle, this gave the living area an extra-low floor and lots of headroom.

The GMC looked sharp from the start, sitting low on its haunches. But the front wheel drive gave traction problems on uphill grades, especially in heavy rain or snow. Handling was otherwise decent, helped by a low center of gravity and an air spring setup for the four wheels at the back.

You got the choice of a six-berth 26-foot or a (relatively rare) four-berth 23-foot. The sleek styling gave an amazingly low drag coefficient of 0.39. And the interior was funky even by 70s standards, designed with the help of House and Garden magazine. The wraparound glass looked cool, but in hot weather the large windows put a huge strain on the roof-mounted air conditioner.

At launch, the GMC cost between $12,000 and $16,000. And what a launch it was: the stock prices of all the other major RV manufacturers fell the very next day. Their vehicles suddenly looked very old. As the GMC sales brochure said, you could now buy a “motorhome that doesn’t look like a box or ride like a truck.”

GM originally pitched its motorhome as a ‘multi-purpose vehicle’ for extended living. That was mostly a marketing fantasy, but in 1975 GM did launch an unfurnished Transmode model. Soon, GMCs were being turned into everything from mobile recording studios to laboratories. The Transmode shells were farmed to conventional coachbuilders such as Coachmen, and even Coca-Cola got into the game, offering custom ‘Gadabout’ models as prizes.

And then, suddenly, the wheels came off the bus. The fuel crisis played a part: the GMC’s 8 to 10 mpg thirst was actually pretty good for a Class A with a big V8, but the running costs became too much for the American middle classes.

In 1977 GM shrank the engine to 403 cubes, but the sticker price had already soared to $38,000. There was no place for the world’s coolest RV any more: in 1978, the production line in Pontiac, Michigan was shut down.

12,921 GMCs were made in all, and many are still on the road today. Winnebago released a thinly-veiled copy in the late 80s called the Spectrum 2000, and small numbers of other GMC replicas have been produced by companies such as Silver Motor Coach.

Today, thirty years on, the originals are relatively easy to keep on the road. Rebuilt engines are available for $3,000 or thereabouts, and the bodies are made from long-lasting aluminum and fiberglass.

Some owners restore their GMCs to showroom condition, while others update the interiors in superyacht or Airstream CCD style. The only real bugbear is the underlying frame—which could cost up to $10,000 to fix if decayed. But a thriving restoration industry makes it easy to keep the mechanicals in good running order, led by specialists such as Cooperative Motor Works.

GM itself briefly raised hopes for a Mk II Motorhome with the award-winning GMC Pad design concept in 2005. But nothing more has been heard of this. The future of modern RV design probably lies more in the direction of VW’s acclaimed 2001 Microbus Concept.

There are plenty of GMC links to stoke your appetite, from Flickr sets to extensive histories. The best GMC fansite of all is probably bdub, with its archive of GMC brochure eyecandy and a thorough GMC FAQ for newbies. If you’re hankering after a GMC for yourself, keep an eye on eBay or the big RV classifieds such as rvt.com.

Just remember to set aside $20,000 on top of the purchase price, and then you can create a personalized RV that looks like it’s just rolled off the set of The Jetsons. A much better—and cheaper—proposition than a 40-foot white box with cheesy graphics.