Vintage 1976 GMC Birchaven Tour, General Motors GMC Model 230 (23feet) Transmode Coachman Birchaven

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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.

Travelling Machine:

The emphasis for the design was to be on the travelling 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. (Source: https://gmcmotorhome.com/faq/what.html)

I hope you enjoyed the brief history of the GMC Motohome and the tour of the 1976 GMC Birchaven.

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