1977 downsizing, was still using the conventional rear-wheel-drive layout.) 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 tanks. 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 the solid axle found on most front-engined motorhomes. As a result, the floor could be built with about 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 that 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 reversible sleeve airbag 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 or 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 for the coach and for the coach. All GMC Motorhomes are wide and about tall including the usually-installed roof air conditioner. Interior head room is . Gross vehicle weight rating for the coach was and for the coach. Most GMCs with factory interiors have a freshwater tank and a 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.