GMC motorhome

The GMC motorhome was built from 1973 to 1978 in Pontiac, Michigan.

Introduction

The GMC motorhome was the only complete motorhome built by a major auto manufacturer in U.S. automotive history. The project was undertaken by the GMC Truck Division of General Motors, producing what they hoped would be their "halo" vehicle. 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 a 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 to people movers to mobile training facilities to ambulances.

Design and Specifications

The motorhome had a front wheel drive transaxle used in the Oldsmobile Toronado and Cadillac Eldorado with an Oldsmobile 455 cu. (7.5 liter) V8 from the Toronado, but the later models made use of the 403 cu in. (6.6 liter) 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-gallon tanks.

The GMC was equipped with front disk 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" 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 two-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 or 26 feet 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 for the 23' coach and 160 inches for the 26' coach. All GMC motorhomes are 96 inches wide and about 9 feet tall including the usually installed roof air conditioner. Interior head room is 76 inches.

Gross vehicle weight rating for the 23' coach was 11,500 pounds and 12,500 pounds for the 26' coach. Most GMC's with factory interiors have a 30-gallon freshwater tank and a 30-gallon 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. GMC's 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 GMC's retain a reputation as being the most restorable and rebuildable of vintage motorhomes. Many formerly abandoned GMC's 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. GMC's were optionally supplied with generators from Onan in 4000 watts and 6000 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 9-11 miles/gallon of regular unleaded fuel. GMC Motorhomes tested via a wind tunnel were reported to have a drag coefficient of .31, which is typical of modern sedans (though offset by the large frontal area).

Production

12,921 GMC motorhomes were produced from model years 1973 to 1978. Over 7000 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.

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.

In popular culture

*A GMC motorhome served as the base vehicle for the fictional U. S. Army EM-50 Urban Assault vehicle in the 1981 film "Stripes".
*A GMC motorhome is used as a Storm chaser vehicle on the movie Twister
*Max Tennyson drives a GMC motorhome on the Cartoon Network animated TV show Ben 10.
*A GMC motorhome is featured by Shooter Jennings (Waylon Jennings's son) in his music video "FOURTH OF JULY" and is even referred to in the lyrics. It is the opening shot, too, and is obviously well-loved.
*Mack Bolan uses a modified GMC motorhome (complete with mounted rocket launchers and machine guns much like the fictional EM-50 above) for a "War Wagon" in some of The Executioner novels by Don Pendleton, "et al".

External links

* [http://www.GMCers.org]
* [http://www.bdub.net]
* [http://www.gmccoop.com/ Cooperative Motor Works]