The Kitten with a Fat Cat's Heart
The 1955 Jaguar 2.4 raised the bar as one of the first streamlined monocoque family cars reflecting Jaguar's competition success. Note the slender cast grille and enclosed rear wheels.
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The Kitten with a Fat Cat's Heart

By JoeKenwright - 01 October 2012
The 1955 Jaguar 2.4 raised the bar as one of the first streamlined monocoque family cars reflecting Jaguar's competition success. Note the slender cast grille and enclosed rear wheels.

The Kitten with a Fat Cat's Heart
The first Jaguar 3.4, tagged Mark I in retrospect, was one of the world's first muscle cars after Jaguar added the 3.4-litre engine from its Mark VIII limousine to its compact family car entry, the 2.4. It was also Jaguar's first monocoque or unitary body and the 2.4's 1955 arrival marked the point globally when saloon cars overtook purpose-built sports cars in technology and performance.

In Australia, it had a big impact. It not only made a rapid interstate cruiser over relatively poor local roads then compact city runabout when you got there, it was an accessible and relatively affordable track contestant.

Fully-optioned Mk I 3.4 versions equipped with close-ratio gear boxes and overdrive, wire wheels and all wheel disc brakes were as close to a GT-HO Phase III that you could buy in the late 1950s. With a top speed of 193km/h, a standing ¼ mile of 17.2 seconds and 0-96km/h time of 9.1 seconds straight off the showroom floor, it was at least as quick as a GT-HO in relative terms. It was only after the Americans followed the Mk I formula of a compact body (such as the Mustang) with a big engine from larger models and the British did the same with smaller models (such as the Mini), the race track domination of the Mk I and its Mk II successor ended.

In the desirability stakes, the emotional, bespoke wood and leather appeal of the Mk I and its Mk II successor has never waned. As the Mk I 3.4 is better understood as the original and therefore purest expression of Jaguar's compact saloons, it has become sought-after globally. This revival is almost too late, as most have since succumbed to a hard life and serious structural rot.

Mark I Development
As the Mark VII and XK140 netted valuable export dollars for Jaguar and Britain, Jaguar realized that it was in a vulnerable position selling only a top shelf saloon and a specialist sports car. It also needed greater economies of scale for the advanced and costly twin-overhead camshaft inline six-cylinder drivetrain.

The company identified a clear gap for a sedan in the upper middle-class price range. British offerings from Rover, Humber and BMC Riley/Wolseley in 1955 were stodgy and aimed at older buyers. They had little appeal for the younger enthusiast on the way up moving from an XK120 or Austin-Healey sports to make room for a family or business clients. Older, well-heeled drivers but young at heart were also neglected.

It was exactly this scenario that defined the look of the Mk I. As with all Jaguars shaped under the William Lyons regime, full-sized proposals were assessed outdoors in typical Jaguar settings.

Jaguar's Le Mans activities and streamlining experience dictated a smooth aero look. The rear was influenced by the current MK VII/VIII range with several components shared across both models including the bumper profiles and tail lights. The rear spats also linked the two models.

The front was very close to the XK140 update of the XK120 sports. A major departure was the integrated sidelamp units which many argue make the Mk I front look more modern than the Mk II that followed. For a shape as advanced as this to be completed and running as a prototype on roads in 1954 is amazing.

Because this was Jaguar's first monocoque, it was no cheaper to build than the bigger Mk VIII. The one-piece door pressings were an attempt to cut labour costs and contribute to the hewn from a single billet look lost in the Mk II facelift.

The most controversial feature was the rear track, over 114mm narrower than the front. Was it so that Jaguar could fit the full rear wheel spats to link it with the Mk VIII? Was it because Salisbury couldn't supply a wider rear axle? Was it generated by the current belief that a wider front track provided extra stability at speed? Or was it because Jaguar wanted the plan view of its new model to resemble the tear drop, regarded as the optimum aero shape at the time?

All of the above have been suggested. The inability to obtain a wider live rear axle is the least likely as it is relatively cheap and simple to extend a live rear axle as Holden showed with the VN Commodore. Creating space for the spats may have been a partial reason after Jaguar opted to delete the side-sculpturing featured on its XK140 and Mk VIII stablemates. The similar footprint of the Citroen DS19 that was launched at around the same time would suggest that the straight line stability and aero shape issues are the most likely explanations.

The narrow rear track was a convenient scapegoat for any Mk I handling deficiencies but as the racing experience showed, there were other shortfalls that were at least equally to blame, if not entirely.

To fit Jaguar's bulky twin overhead cam six under the streamlined bonnet, Jaguar fitted a low profile inlet system, pancake sump design and remote air cleaner.

Jaguar's First Monocoque
Because of Jaguar's relatively short history as a specialist side car and body builder on separate chassis, Jaguar had to enlist the expertise of the Pressed Steel Company for its first unitary body. The result was a much stronger body shell than it needed to be. This set it up for a much bigger engine than initially planned and the illustrious racing career that followed.

The shell consisted of numerous box sections that not only provided exceptional strength but also made the structure vulnerable to condensation and extreme rot. The rear seat pan, ribbed floor, rear bulkhead and outer sills all contributed and were just as vulnerable. Although quite short in length, the new shell featured a wheelbase significantly longer than an FE Holden hence the nice balance and relatively short overhangs.

Amongst its many refinements which helped establish Jaguar's modern reputation for ride refinement and handling, was the massive cross-beam front suspension and steering subframe mounted on rubber. To access the engine sump for anything other than a basic oil change, the front end had to be dropped.

Although the rear suspension was a live axle with leaf springs, over half of each inverted leaf spring was mounted on rubber, inside the structural box sections on both sides. The rear axle was attached where the rear shackles would normally be on more conventional designs allowing each cantilever leaf spring to act as a trailing arm attached beneath the axle. A pair of upper control arms also acted as trailing arms above the axle while an adjustable Panhard rod controlled sideways movement. Angled telescopic dampers provided additional location. For a 1955 release, this was quite sophisticated.

A special 2.4-litre engine was created using the 3.4-litre bore with a much shorter stroke which reduced bonnet height and shaved significant weight from the front end. The 2.4 version was presented as a fairly basic entry model with a Special Equipment option. By 1956, the 2.4 was entered in a cross-section of competition activities. Never an outright contender, it was a podium finisher and a frequent class winner.

Following the October 1955 launch, booming sales in the US and Europe saw William Lyons awarded a Knighthood in 1956 at the tender age of 54. By February 12, 1957, Sir William was faced with ruin after 25 per cent of his Browns Lane facility was destroyed by fire. Over 500 cars were damaged or destroyed including advance stocks of the yet unannounced Mk I 3.4. The fire also killed the exciting new D-type based XKSS sports car in its tracks.

Pick the later 3.4 with its wider grille and cutaway rear wheel spats.

The 3.4 Finally Arrives
After an amazing combined effort by loyal workers and suppliers, Jaguar announced the 3.4 on February 26, 1957. It featured the same engine as the latest XK150 sports car with a special inlet manifold and air filter along with a similar sump to the 2.4 so it could fit under the bonnet. Cooling, engine mounts, bigger clutch and rear axle with beefier Mk VIII internals were part of the package. Front springs and an upgraded rear Panhard rod mounting anticipated the extra weight and forces involved.

Gearing was tweaked to exploit the low speed extra torque and top end performance.
The old Moss manual gearbox continued as standard but could be optioned with the usual Laycock-de Normanville electric overdrive and shorter final drive ratio. The big engine allowed the Borg-Warner Model 8 automatic to be offered as an option and was an instant success in the US.

Appearance tweaks were dictated by the extra grunt and heat. The 2.4's quaint and narrow cast grille was replaced by a much wider, fabricated fine bar grille, similar to the XK150 sports, which in turn dictated different front panels. The cutaway rear spats and twin exhausts, on the opposite side to the 2.4's feeble single pipe, added real street credibility. The 3.4 exhaust note was music to the ears of 1957 enthusiasts.

That wasn't all. The big news came later in 1957 with the pioneering all-wheel disc brake option, Jaguar drawing on the D-type's success in Le Mans 1955 to establish their credibility. They came only with the wire wheel option, a practical but clever ploy that graphically displayed the new technology whether a Mk I was parked or on the move! All disc-braked 2.4 examples had to be fitted with the 3.4's cutaway rear spats. Factory kits were offered to retro-fit the new brakes to earlier cars. The only downside was that Dunlop had not yet worked out a caliper design that allowed the pads to be changed without dismantling the brakes.

By 1958, this had helped double 3.4 orders over the previous year. As with local muscle cars, the widespread take-up of the Mk I 3.4 as a police pursuit car encouraged Jaguar to offer packages with close-ratio gearboxes, uprated springs and dampers and stronger electrics. The 3.4 engine could be ordered in three states of tune including a 9:1 high compression version.

Whitewall tyres and automatic option enhanced 3.4's appeal to the Americans although the driving lights shown on this example were deleted on US export cars.

Running changes included new rear springs and different rear axle geometry, bigger front suspension ball joints, revised quick change brake calipers and 72 spoke wire wheels. These were amongst the many improvements dictated by the new model's high speed application and track use. The scene had been set for track domination.

Le Mans racer and works driver Mike Hawthorn became one of the Mk I's biggest fans and proponents using his race-prepared example as a road car. In January 1959, he lost control of the car on the way to a charity event and died after it hit a tree. Subsequent investigations cleared the car, which had been fitted with a much wider rear axle. An unfavourable combination of speed, slippery conditions, driving rain and crosswinds was deemed the likely culprit.

Hawthorn's death had exposed how a full house Mk I 3.4 had long ago outrun the skinny Dunlop RS4 cross-ply tyres fitted since April 1958. The Mk I 3.4's towering performance and braking capabilities were a classic case of exposing the next area that needed a breakthrough development. In 1959, it was the pathetic capabilities of even the best road tyres that needed urgent attention. Jaguar later played a key role in encouraging the British tyre industry to lift its game to meet its new models.

Mike Hawthorn's untimely death was an unfortunate association for the Mark I 3.4 in its final year but it was not an isolated incident as celebrities and experts alike came to a grim end in top shelf performance cars that had long ago outgrown 1950s tyre technology.

Later 2.4 examples gained the wider 3.4 grille but retain the enclosed rear wheels unless fitted with wire wheels and disc brakes.

The Mk I 3.4 in Australia
Because of the favourable trading situation between Great Britain and Australia, the Jaguar MK I 3.4 was one of the most affordable and desirable performance cars locally. At $5110, its closest rivals were the Daimler Century, Studebaker and Mercedes-Benz 220S.

A report in Australian Motor Manual in May 1958, provided some insights into who was buying the Mk I and why.

"The agents say that most of the new 3.4's have been sold to ex-Mk VII owners. Due to their size and handiness, the 2.4 and 3.4 are excellent city transports but in the hands of the Mk VII owner who expects another docile touring car for his money, they can be sporty or dangerous, according to the driver's ability."

"This was evidenced first hand recently when spending a couple of days in Sydney where a number of the new cars have been sold, we saw eight models with bent radiator grilles, guards and bonnets."

"Docile in top gear down to 15mph/24km/h, the 3.4 turns into a snarling rocket when the right foot is depressed at the same speed in second gear."

The local verdict?
"Although low-priced the 3.4 is nevertheless a quality car of the highest order. Its design won the American Artists Magazine Award."