1973 GMC Motorhome. Click image to enlarge
Story and photo by Bill Vance
In the early 1970s, General Motors decided to enter the motorhome business. At the time, it would be the only automobile manufacturer to produce a complete recreational vehicle. Many supplied chassis and running gear to RV builders, but GM decided to do the job entirely themselves, although they did provide unfinished bodies to others who wanted to complete them with their own customized features.
The announcement of a motorhome by such a formidable company sent chills through the industry causing shares of established RV manufacturers to fall into a slump, although they would eventually recover.
GM didn’t want its motorhome to be the traditional utilitarian box-on-wheels, but rather a low, sleek, easy-to-enter design statement that would not only be handsome, but would have car-like driving characteristics.
To achieve the desired low silhouette a new approach was required, and fortunately for the GMC Truck Division which was assigned the project, GM had the perfect drivetrain: the front-wheel drive engine and transaxle unit introduced in the 1966 Oldsmobile Toronado, and later used in the Cadillac Eldorado.
The 7.5-litre (455 cu in.), overhead valve Toronado V8 was mounted longitudinally, with the three-speed Hydramatic transaxle unit rotated 180 degrees and mounted on the left side of the engine. Power went to the transmission via a 51 mm (2 in.) wide chain. Since normal coil spring suspension would have interfered with the halfshafts, front suspension was by longitudinal torsion bars.
Placing the entire drivetrain in the front of the vehicle eliminated the long driveshaft. This was complemented at the rear by using a pair of tandem wheels on each side. Eliminating the rear axle allowed the floor to be only 356 mm (14 in.) above ground, lowering the centre of gravity and removed the need for a step for entry and exit. Another advantage of the tandem wheels was that the wheel wells intruded minimally into interior space.
The tandem rear wheels were suspended on each side by a bogie arrangement and an air spring inflated by an on-board compressor. This provided automatic load levelling for travelling, and allowed manual levelling when setting up in an RV park. It also provided good riding qualities for a motorhome. Braking was by discs in front and drums on all four rear wheels.
For long life, the aluminum body skeleton was mounted on a ladder-type steel frame and the motorhome was stylishly clad in aluminum and fibreglass. It was fitted with large windows, which were impressive looking and wonderful for visibility, but placed an extra load on the air conditioning unit.
Sleeping accommodation for up to six was provided by converting seats; there were no permanent beds. Although the GMC motorhome came in 7,010 mm (23 ft) and 7,925 mm (26 ft) lengths, the longer one was far more popular. Width was 2,438 mm (96 in.) and the nicely appointed interior had a height of 1,930 mm (76 in.).
Overall height was 2,743 mm (108 in.), including the roof-mounted air conditioner. Wheelbases were 3,556 mm (140 in.) and 4,064 mm (160 in.) respectively, measured from the front axle to the centre of the bogie between the rear wheels. Weight was in the 5,443 kg (12,000 lb) range.
The GMC motorhome could be reasonably self-sufficient with an optional 4,000 or 6,000-watt generator set, and two 113-litre tanks for potable water and wastewater. One thing it was short of was externally accessible storage space for all the paraphernalia like tools, extension cords, ropes, etc., that campers often carry.
With ample power, a low centre of gravity, power steering and cruise control the GMC could cruise easily at normal highway speeds. It used regular gasoline at the rate of about 28 L/100 km (10 mpg) from two 96-litre fuel tanks. This was quite competitive with the fuel consumption of other motorhomes, thanks in part to an aerodynamic body with a drag coefficient of only 0.39, which was good for this type of vehicle. The only downside of the front-wheel drive was reduced traction in hilly campgrounds under slippery conditions.
The GMC motorhome was manufactured in Pontiac, Michigan, and introduced in 1973. It was made until 1978 and remained basically the same vehicle for its entire production period. With fuel economy and supply concerns rising in the mid-1970s, the motorhome’s Oldsmobile engine was reduced to 6.6 litres (403 cu in.) in 1977.
A total of some 13,000 GMC motorhomes were built over the six-year run. Upon their introduction they quickly began attracting a dedicated following, an enthusiasm that extends to today, over 30 years after production stopped.
Many current owners have modernized them with better materials and newer engine technology. There are clubs devoted to preserving and enjoying them, and companies that stock parts for the amazing 9,000 estimated to still be in use.
Although it is doubtful that General Motors made much, if any, money on its GMC motorhome venture, it did build a lasting legacy. It’s a good example of what the huge resources and talent of a large company can do when it turns its mind to something different.
Click here for more information on the GMC Motorhome.