XK Development and Compact Saloons

Whilst Jaguar was enjoying success in motor racing, its road cars were also benefiting from their own development as well as technologies that stemmed from the development of the race cars.

Jaguar XK140

In October 1954 the XK140 was introduced as the successor to the XK120. It used the same body pressings as the XK120 and was available in roadster, fixed-head and drophead forms, but was considerably different under the body. The chassis was almost exactly the same as that of the XK120 except that the engine was moved forward 76 mm to make more room in the cockpit and improve weight distribution from 48% front and 52% rear, to nearer a 50/50 split. The central cross-member was modified to allow an overdrive made by Laycock to be fitted as an option, the battery and bulkhead positions were changed, and rack and pinion steering was fitted. The rack, which had been developed for the C-Type, transformed the car in conjunction with the revised weight distribution and more up-to-date shock absorbers.

On the fixed-head coupé, the bulkhead was reshaped rather than being moved to give a similar effect without having to change the roof pressing, although the roofline was raised by 25 mm to heighten the impression of airiness in the cockpit. The extra space liberated in the drophead and fixed-head coupés was used for two tiny rear seats, which made the cars more appealing to families with small children.

The special-equipment XK120’s engine was used as standard equipment on all XK140s, with a single exhaust to give 180 bhp, or with a high-compression C-Type head and twin exhausts to give 210 bhp. The standard XK140 was called the XK140M in the United States (because of its ‘modified’ engine) and the XK140 with the C-Type head was referred to as the XK140MC.

A close-ratio gearbox, which had been available as an option on XK120s since 1953, was now standardized, and more cars left the factory with wire wheels in place of the solid steel wheels.

Although externally very similar to the XK120, the XK140 could easily be identified by its bumpers, which were similar to those of the Mark VII saloon and gave better protection against clumsy parking. The radiator grille (with a new cooling system) also marked the cars apart, and offered better protection against overheating in traffic.

The Mark 1 Saloon

In 1955 Jaguar introduced the Mark 1 compact saloon to fill the niche between its two-seater sports cars and the larger six-seater Mark VII. The Mark 1 was a 2.4-litre car designed from the start with an eye to economy, but such was its potential that it was soon given the larger 3.4-litre engine to make it one of the fastest saloon cars in the world.

What really set the Mark 1 apart from all other Jaguar saloons, was its unitary method of construction – a new venture for Jaguar. This type of body – in which the basic shell doubled as the chassis – had two significant advantages: that it saved weight and was inherently more rigid. Stress engineering for cars was in its infancy in the 1950s, so the Jaguar Mark 1’s body shell was, if anything, too strong and heavy, but it was still much more efficient than the older system of separate chassis.

With such as stiff basis to the car, relatively soft suspension could be used, which paid dividends in ride and roadholding. The front suspension was similar to that of the Mark VII saloon, except that it used coil springs rather than torsion bars because Jaguar were not confident that the bodyshell would be strong enough to take the stress of the torsion bar rear anchorage points. The rear suspension used normal half-elliptic springs turned upside down, with one end attached to the live rear axle and the front half clamped to the bodyshell so that they acted, in effect, as quarter-elliptic springs. An adjustable Panhard rod stopped the axle moving sideways and trailing arms prevented it from twisting under power.

The engine was a 2.4-litre version of the XK unit. The capacity reduction, aimed at economy, was achieved by reducing the stroke to 76.5 mm, which enabled the engine to rev faster and helped to make up for some of the power lost by the capacity reduction. The original XK cylinder head – retrospectively called the A type – was used with twin Solex carburettors, rather than SU, to save petrol at the expense of all-out performance. Nevertheless, the Mark 1 was still capable of 96 mph, and an optional overdrive was offered to make high-speed cruising more relaxed and economical.

In March 1957, the 3.4-litre engine was introduced to the Mark 1. The power unit was exactly the same as the one fitted to the Mark VIII saloon, complete with B type cylinder head, SU carburettors and twin exhausts, linked to either a manual or automatic gearbox. The rear axle was strengthened by incorporating Mark VIII components and a larger radiator was fitted. This meant that the front of the car had to be restyled to accommodate a wider radiator grille. The new frontal appearance was standardized on the 2.4-litre Mark 1 six months later, together with cutaway rear spats, which were fitted to the 3.4-litre Mark 1 to help brake cooling.

Mark VIII saloon

In October 1956 the Mark VIII was introduced as a replacement for the Mark VII. The B type cylinder head was fitted, the automatic gearbox further improved, and there was a certain amount of restyling, such as two-tone paint and cutaway spats for the rear wheels. It was also easily distinguished from the previous model in that it had a one-piece windscreen in place of the Mark VII’s which was split in the middle. Towards the end of the Mark VIII’s relatively short production run, in April 1958, some left-hand-drive versions were fitted with power-assisted steering.

XK150

In May 1957 the XK was revised dramatically for the last time as the XK150. Introduced at first in drophead and fixed-head forms, it was bigger and heavier than its predecessor, but a good deal faster in the middle range of its performance. Fitted with the new B type cylinder head, it no only developed 190 bhp, but also gave the engine a lot more mid-range torque. The C type head was still available for ultimate top-end performance. Almost as soon as the XK150 went into production it was fitted with disc brakes all round which – like the C-Type on which they were pioneered – made the new car much faster from point to point.

The chassis and running gear of the XK150 were substantially the same as on the XK140, but the coachwork looked very different. The body was given a raised waistline with bulbous doors and wings to allow the interior to be widened by 102 mm, giving more room for the occupants, who also benefited from a further raising of the scuttle line. Like the Mark VIII, a wrap-around windscreen was also fitted now that glass of the right quality was available, and the fixed-head coupé was given a large saloon-style rear window to make it feel more spacious. Other changes to the body included wrapping the bumper around the flanks for greater protection, and fitting a wider radiator grille for improved engine cooling.

In March 1958 the XK150 roadster was introduced. Being a lighter car it was faster, even more so when it was fitted with an option straight-port cylinder head and triple carburettors, which increased the power to 150 bhp. In this form it was known as the XK150S. The brakes were also improved by fitting square quick-change pads developed on the D-Type in place of the older round type.

In October 1959 an enlarged engine was offered on all XK models: the 3.8-litre unit which had been under development by the factory since it was first use on a D-Type in 1956. The bore was increased to 87 mm in a new block with dry liners.

Available in several configurations, the top of the range XK150S 3.8-litre as it was known, produced 165 bhp with a 9:1 compression ratio straight-port cylinder head and triple SU carburettors.

Mark IX

In October 1958 the Mark IX was introduced. Virtually the same as the Mark VIII it had the new 3.8-litre engine that was to be fitted to the XK150S a year later, and disc brakes all round. The new engine had much more torque than the 3.4-litre unit and greatly improved driving flexibility, as well improving outright performance, raising the top speed from 106.5 mph to 114.4 mph. The Mark IX continued in production until late in 1961.

Mark 2

In October 1959 the Mark 2 saloon was introduced as a replacement for the Mark 1. The changes that were most readily apparent were in appearance. The windows were made larger, mainly by using more slender roof supports now that it had become evident that those on the Mark 1 were thicker than necessary. The rear axle was also made much wider to remove the crab-tracked appearance, much improving the new car’s stability. The interior was also redesigned, retaining the traditional Jaguar image, but appearing more modern at the same time.

Three new engine options became available on the Mark 2, all using the B type cylinder head: the 2.4-litre which produced 120 bhp; the 210 bhp 3.4-litre; and the Mark IX’s 3.8-litre engine producing 220 bhp, which gave the Mark 2 a top speed of 125 mph with a 0–60mph acceleration of 8.5 seconds.

An automatic transmission was an option on all versions of the Mark 2, and the 3.8-litre model also had a limited-slip differential fitted as standard to counteract the ‘tail wag’ that the additional engine torque could produce.

The Mark 2 cars were to rank amongst the best-loved Jaguars ever made, with many enthusiasts still regarding them as ultimate classics. Most will recognise the Mark 2 as the car driven by fictional TV detective Inspector Morse, played by John Thaw. The 3.8-litre car in particular gained a reputation as being particularly capable (especially for bank raids), being fast and with room enough for five adults, and were often depicted as getaway cars in television shows.