York City limited the wheelbase of taxis to 120 inches, Checker was ready with a brand-new body that would form the basic styling until the end of production in 1982. This was the A8, which featured slab-sided, boxy styling for the first time. The A8, produced from 1956 to 1958, had single headlights and a heavy bar-type grille in front, with high-mounted taillights resembling the 1953 Chevrolet. The basic chassis and drivetrain, however, remained similar to previous models going back to the 1939 Model A, including its Continental F-226 "Red Seal" inline 6 cylinder engine. The body was designed to simplify maintenance, as exterior panels were fastened by bolts and could be replaced without special tools or welding; the front and rear bumpers were interchangeable. The X-frame chassis used a Dana 44 rear axle on leaf springs with an independent front suspension that used some components from the 1954 Ford models. The A8 was equipped with drum brakes and a three-speed manual transmission. Model A9 (1958) For 1958, a restyle of the A8 was introduced, the A9. It featured dual headlights, and a revised egg-crate grille with parking lights built in, surrounded by a "starburst" design. Shortly after the A9 was introduced, Checker began marketing their cars to the general public, the first of these being the A10 Superba, which was a "civilian" A9 with the taxi equipment removed. The Superba was available both as a four-door sedan and as a station wagon. The wagon was designated A10W. Model A11 (1961) The A11 (sold to the public as the A12) was introduced in 1961 and incorporated quad headlamps. During the 1960s, Checker usually managed to meet its target volume of 6,000-7,000 cars a year. In 1962, production topped 8,000, most of which were taxis. In 1964, the state of New York pursued Markin and Checker on antitrust charges, alleging that it controlled both the taxi service and manufacture of taxis, and thus favored itself in fulfilling orders. Rather than allow Checker drivers to begin buying different brands of cars, Markin began selling licenses in New York City. The next year, the company switched from the Continental inline six engine, offering either Chevrolet overhead-valve I6s or small block V8s. The Continental F-226 was an L-head design that was built for reliability and longevity with an output of ; however, the special features meant they were sold to Checker at a loss,