Jaguar's Mark X sedan came at a time when the company was going from strength to strength in other areas, too. Its XK sports cars were consistent sellers throughout the Fifties, helped by numerous competition successes at places like Le Mans, where Jaguar won the 24 Hours in 1951 with the C-Type and in 1955, 1956, and again in 1957 with the aerodynamic D-Type. It was for such feats that William Lyons was knighted in the Fifties.
Jaguar had also ventured into unit construction with a smaller, less costly sedan in 1956, the curvaceous XK-powered 2.4-Litre four-door, which in 1959 evolved into the even more popular Mark II series of 2.4-, 3.4-, and 3.8-liter models. At the same time, Jaguar was readying the elegant, exotic E-Type, its most stunning production sports car yet.
But Coventry hadn't forgotten about big sedans, and a new one arrived in the E-Type's debut year of 1961. Predictably, it was called Mark X. It took a long time to develop -- so much so that doubters within the company dubbed it the "Mark Time." The reason was that unit construction had worked so well on the small sedan that Sir William wanted it for this new big one. He also wanted to jump Jaguar styling a full generation ahead so as to compete more directly on that basis with American luxury makes.
As a result, the only things the Mark X inherited from the Mk IX were its 120-inch wheelbase, 3.8-liter engine, and transmission choices. Engine tuning owed much to the rapid E-Type. So did the rear suspension, a new fully-independent setup with coil springs and classic double-wishbone geometry, plus inboard disc brakes. Styling was completely different, of course, still with four doors but much smoother, marked by flow-through fenderlines, a gracefully tapered tail, a slimmer front bearing a more modest grille, and a rather low-profile roof.
The new unitized body/chassis and extremely wide track dimensions allowed the Mark X to sit fully 8.25 inches lower than the Mk IX, yet be just as roomy inside. At 202-inches long overall and 4,200 pounds, it was the biggest, heaviest Jaguar yet. Even so, its 265 horsepower was good for a top speed of 120.
The Mark X stood to be quite popular at initial selling prices of £2,256 in the UK and $6,317 in the U.S., but it always had to struggle for sales against the more agile, less costly Mark IIs, particularly the 3.8-liter version. Then too, its styling turned out to be a shade too "transatlantic" for most Europeans yet was a bit too conservative for Americans, and the whole car just seemed too large, too wide, and too extravagant. Sales thus proved disappointing: 13,382 over three years.
Attempting to turn things around, Jaguar substituted the E-Type's 4.2-liter six in 1964. Though there were no visual changes and rated horsepower was the same, the big-bore engine's extra torque meant low-speed flexibility that made for easier, more responsive town driving. But it did nothing for Mark X sales, which again disappointed at only 5,137 units through 1965.
The following year brought minor external trim changes, a slightly more luxurious interior and a new name, 420G, the last bringing nomenclature into line with the latest 240/340/420 evolutions of the Mark II. But sales tailed off quickly, ending in early 1970 at just 5,763 units. (Incidentally, some 42 Mark X/420G limousines were built in 1965-1970, identical to the owner-driver models save the customary division window.)
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