all of these years. The Estate Wagons, as with other GM full-sized wagons during these years, used a rear suspension with multi-leaf springs instead of the coil springs used on other full-sized Buicks, and other full-sized GM cars to better cope with load carrying duties. The Estate Wagons also featured a new 'clamshell' tailgate design, marketed as the Glide-away Tailgate, where the rear power-operated glass slid up into the roof as the lower tailgate (manually or with power assist), slid into a recess under the cargo floor. Ultimately, the manual lower tailgate was supplanted by the power tailgate. The tailgate system was operated by switches on the instrument panel or a key switch on the rear quarter panel. Like a top-hinged tailgate, the clamshell design allowed a user to stand directly at the open cargo area without impediment, facilitating loading and unloading in tight spaces. the rear seat could be folded flat for additional cargo, and incorporated a 60/40 split so that extended cargo and passengers could be accommodated, and providing entry to the third row seat. Cargo capacity with the second row seats folded was 184 cubic feet. If passengers were seated in the optional forward facing third row seat, the rear window could be retracted into the roof while the vehicle was in motion with the tailgate in place. In its first year, 24,034 Estate Wagons were sold with a listed retail price of US$5,414 ($ in dollars ). At shipping weight, or about curb weight, the three-seat 1974 Estate Wagons are easily the heaviest Buicks ever built, even heavier than the Buick Limited limousines of 1936–42. The 1975 and 1976 models were the longest station wagons ever built. The Estate used the Buick 455 V8 from 1971 through 1976 found in the Buick GSX. The Stage One high performance version, with high lift camshaft, enlarged ports, enlarged valves, and dual exhaust, was available as an option through 1974. To commemorate the Bicentennial of the United States, the standard colors available on all Buicks were Judicial Black, Liberty White, Pewter Gray, Potomac Blue, Continental Blue, Concord Green, Constitution Green, Mount Vernon Cream, Buckskin Tan, Musket Brown, Boston Red and Independence Red, with specially available colors on select models Congressional Cream, Revere Red, Colonial Yellow and Firecracker Orange. 1977–1990 In 1977, the Buick Estate was downsized and relaunched on General Motors' B-body. In 1979, an Estate Wagon Limited was