Thanks to Peter Young of www.jaguartrader.com for allowing us to use this article

Since the launch of the original XJ6 in September 1968, Jaguar has made six generations of XJ series saloons, which between them have reached a total production figure of over 800,000 cars - in other words, more than half of all Jaguars ever built are XJ models. Originally introduced as a single model range to replace no less than four different predecessors, today the XJ saloon stands at the top of the expanding Jaguar range, as the largest and most prestigious of three saloons. And for many loyal Jaguar customers and enthusiasts, the XJ is still the definitive Jaguar saloon.  The story of how the original XJ came about, and how the range has developed over the years, is part of the Jaguar legend, and provides a fascinating insight in how the company has remained true to the same ideals over the past 35 years, while always adapting to changing requirements, and staying at the forefront of contemporary engineering and design. The XJ range also represents a direct link with Jaguar's founder, Sir William Lyons (1901-1985). The original car was his inspiration, his vision of Jaguar's future as he saw it in the 1960s. The success of the XJ models over the years is his best memorial. 
 

During the 1960s, the Jaguar saloon range consisted of the best-selling Mark 2, a compact sports saloon, together with two intermediate models derived from this, the original S-type and the 420, while at the top of the range was the Mark X or 420 G model - a limousine-like prestige car. With this extensive range, Jaguar catered for every niche of the prestige market, but production of so many different models in relatively small numbers was a headache. Of the four ranges, there were altogether seven Jaguar and two Daimler models, using four different sizes of the famous six cylinder XK engine, as well as the Daimler V8. So the idea emerged of replacing all of these cars with a single model range, offered with a choice of just two engines, and available in both Jaguar and Daimler forms. The size and package of the new car was chosen so that it would be a replacement for the medium-sized S-type and 420
models, which were considered to be the ideal size for a future Jaguar model with international appeal. 

The car that became the XJ was originally known by its internal project number, XJ4. Here XJ stood for 'eXperimental Jaguar' and there was no particular significance to the number 4. The germ of the project was a proposal to replace the E-type with a four-seater GT model, in response to such cars appearing in Jaguar's important American market - for instance the Buick Riviera. The styling of the bodywork, as ever overseen by Sir William Lyons, therefore originally featured front and rear ends rather like the E-type, and the body also only had two doors.

Later as the project progressed, the emphasis was once again on a new saloon model, so rear doors were added, and the front and rear ends were cut off, producing the typical XJ look, with the customary style and elegance expected of a Jaguar. The front end was modelled on the Mark X and 420 models, with a wider and lower version of the Jaguar grille and four headlamps. The grille was perhaps controversial, with its cross-hatch of vertical and horizontal bars. The car was considered so unique and distinctive that early examples did not have a Jaguar nameplate! - only the 'growler' and 'leaper' badges. The interior was typical Jaguar, with leather upholstery, wood trim, and a full range of instruments. 

The car was engineered under the direction of the late Bob Knight. He was already responsible for the Jaguar independent rear suspension, which in modified form was used on the new car. Bob's expertise was in developing suspension which combined impeccable road manners with a high degree of ride comfort. With sub-frames for both front and rear suspension and clever use of rubber mountings, the XJ set new standards in suppressing noise, vibration and harshness. A new feature was the anti-dive geometry of the front suspension, and for the first time Jaguar used rack-and-pinion steering on a saloon car, with power assistance standard on the 4.2-litre model. Brakes were discs all round, with dual circuits. To suit the characteristics of the suspension, Dunlop developed a new type of wide low-profile radial tyre with a high speed rating. The result was a car that was superb to drive, and
to be driven in. 

It had originally been Sir William's hope that the new saloon car would from the start be fitted with the new V12 engine which was being developed by the team of Wally Hassan, Claude Baily and Harry Mundy. However the V12 was delayed (and would make its debut in the E-type in early 1971), and a V8 derived from the design was still-born. In consequence, when the XJ appeared in 1968, the engine was the well-tried XK straight-six of 4.2 litres, with twin carburettors and 245bhp. As an alternative, with an eye to Continental markets where cars were taxed by engine size, Jaguar offered a new 2.8-litre version of the XK engine. The standard manual four-speed gearbox could be supplemented with an overdrive, while an automatic gearbox was an option. The model name XJ6 was finally chosen simply because the car had six cylinders. 

The launch of the car took place on 26 September 1968, just before the London Motor Show. Sir William Lyons himself appeared in the advertisements for the new car, and declared that this was the finest saloon car Jaguar had ever made. The press agreed with him, and the car was given an enthusiastic reception. The combination of traditional Jaguar virtues such as style and sportiness, performance and comfort, were now enhanced by the advanced engineering of the XJ, and its remarkable refinement. Comparisons began to be drawn between the Jaguar XJ and the Rolls-Royce. 

The Jaguar quite simply set a new standard, especially at its price - a basic  2.8-litre model cost just £1800 (albeit lacking a few creature comforts, and with Ambla rather than leather trim, which would add £100 to the price) and even a 4.2-litre automatic was only £2400. At the same time, the 4.2-litre car with manual gearbox had a top speed of 124mph, nearly 200km/h, and accelerated from 0 to 60mph (96km/h) in a still respectable 9 seconds. In Britain, Car magazine chose the XJ6 as their 'car of the year' - although the European 'Car Of The Year' title was denied Jaguar. 

Demand was such that for quite some time, Jaguar found it difficult to make enough XJs, and there were considerable waiting lists, both in home and export markets, while at the same time, some nearly new second-hand cars changed hands at well over list price. The supply position eased up after the first two years, as Jaguar now dropped all the earlier models and concentrated on the new car. In 1969, the expected Daimler versions followed, bearing the model name Sovereign from the immediate predecessor in the Daimler range. At slightly higher cost than the Jaguars, the Daimlers had the classic fluted radiator grille with vertical bars, more luxurious trim, and overdrive as standard on manual cars. 

In April 1971, the magnificent 5.3-litre V12 engine had made its debut in the E-type Series 3, and in July 1972, this engine also became available in the XJ saloon, in this form called the XJ12, while the Daimler version adopted the name Double-Six rom the original V12-engined Daimler of the 1930s. These cars were only offered with an automatic gearbox, and for the first time on a Jaguar, air conditioning was standard. On the Jaguar XJ12, a vertical-bar grille with a V12 badge was used. In the 1970s, the XJ12 and Double-Six cars were the only V12-engined saloon cars available anywhere in the world, and Jaguar made the only V12-engined cars in large-scale production. With a top speed of 147mph, close to 240km/h, the XJ12 also captured the title of the fastest saloon car in the world. 

If there had been any criticism of the original XJ, it was that rear legroom was rather limited for a luxury car. The problem was addressed in September 1972, when a long wheelbase model, adding an extra 4in (102mm) between the axles, was introduced. The first long wheelbase model was the Daimler Double-Six Vanden Plas, with unique luxury trim by the coachbuilder Vanden Plas which also built the Daimler limousine. Features included separate rear seats. It was quickly followed by long wheelbase versions of the other Jaguar and Daimler models. 

Meanwhile, a face-lifted version of the XJ range was under development. A major reason for changing the styling of the original was that the bumper height needed to be raised to comply with new legislation in the US market. This meant that the radiator grille became even shallower, and the cross-hatch type grille was found on both six and 12 cylinder Jaguars. At the same time, Jaguar took the opportunity to revise the interior and improve the ergonomics, with a new dashboard which put all the instruments and major controls in front of the driver. Also as part of the revised range, a two-door
pillarless coupé version was under development. Such a model had been planned already in the mid-1960s, when the trend in the USA was towards the 'hard top' body style. 

The revised Series 2 range was introduced at the 1973 Motor Show. The 2.8-litre model was discontinued, except for limited production in left-hand drive form for export. The short wheelbase four-door saloons were also soon discontinued, and all saloons were from then on built on the longer wheelbase, while the original wheelbase was retained for the new coupé, also known as the XJ-C model. In the case of the coupé, that October 1973 announcement was a little premature; because of problems with sealing the opening rear quarterlight to satisfactory Jaguar standards, series production did not commence before early 1975. 

The coupé, in fact, turned out to be quite short-lived, and these elegant cars with their distinctive standard-fit vinyl roofs and optional alloy wheels, were discontinued at the end of 1977. With a total production figure of just over 10,000, the coupés remain among the rarest - but also the most desirable - of the classic XJ models. The coupé was used for the unsuccessful attempt of the Leyland Broadspeed team to enter the European Touring Car Championship in 1976-77. Although spectacular and very fast, the cars were too heavy, and were never developed sufficiently to overcome reliability problems. 

The saloons continued with the same model variations as before, together with the addition in 1975 of a 3.4-litre engined car, reviving the original size of the  XK engine, and a little later a Vanden Plas-trimmed version of the Daimler Sovereign 4.2. On the mechanical side, fuel injection replaced carburettors on the V12 cars in 1975, and a GM400 automatic gearbox was introduced on all models in 1977. In 1978, six cylinder cars for the North American market followed the V12 by adopting fuel injection. 

It was almost time for a third XJ generation. For the first time in Jaguar history, the re-styling of the next model was entrusted to an external designer, the famous Italian house of Pininfarina. The greenhouse of the car above the waistline was completely re-designed, with a new roof, side windows, and screens, which increased window area and made the car look even lower, although in fact rear headroom was improved. There were also new door handles, bumpers and rear lights, and improvements to the interior, as well as a handsome new vertical-bar radiator grille. Mechanically, the most
important change was that on the six cylinder cars with manual gearbox, a five-speed gearbox was now fitted, and fuel injection was found on all 4.2-litre cars. 

The new models, called the Series III, were launched at the end of March 1979, and with the even more elegant styling, were warmly welcomed, and carried on the Jaguar traditions at a difficult and crucial time in the company's history. 

During 1981, important improvements were made to the V12 engine. A new cylinder head designed by the Swiss engineer Michael May was introduced, with a very high compression ratio of 12.5:1 and other features which reduced fuel consumption by about 25 per cent - an extremely worthwhile improvement on these rather thirsty cars. When fitted with the modified engine, the XJ12 and Double-Six cars became the HE models. In the same year, a Vanden Plas version of the Jaguar XJ6 was offered in the North American market, equipped to the same standard as the home market Daimlers, while  in 1983 the Sovereign model name was transferred from Daimler to Jaguar, and from then on denoted the most luxurious versions of the Jaguars. 

As however the basic XJ design was now well over 10 years old, behind the scenes Jaguar was developing a replacement, now under the project code XJ40. There were several false starts, and many delays, before the new car would eventually emerge on 8 October 1986, just before the International Motor Show at the NEC. Crucial to the development of this car was a new Jaguar engine, intended to replace the classic XK unit. This was originally derived from a single bank of the V12 but had twin rather than a single overhead camshaft, and benefited from having four valves per cylinder. As had happened many years before with the XK engine, and also with the V12, the new engine - called the AJ6, for Advanced Jaguar - was at first launched in a limited production sports car, the XJ-S 3.6 cabriolet of 1983. 

As an alternative to this 3.6-litre version of the AJ6 engine, the XJ40 was also fitted with a 2.9-litre version, although this featured a different cylinder head with a single overhead camshaft and just two valves per cylinder. There was not at first a 12 cylinder version of the XJ40 which had not originally been designed to accept a V engine, and a partial re-design was necessary before the V12 engined model finally arrived in 1993. In consequence, while production of the six cylinder Series III was stopped soon after the introduction of XJ40, the 12 cylinder Series III continued in production, proving the timeless elegance of the classic XJ design, even after more than 20 years. 

As far as styling was concerned, XJ40 was the last Jaguar production car that Sir William Lyons (who died in 1985) had any influence on, as an informal consultant and regular visitor to the styling studio, even in retirement. Perhaps inspired by contemporary 1980s design, XJ40 was rather more angular than most previous Jaguars, and many versions featured large rectangular headlamps, as well as square rear lights. An innovation for Jaguar was the quarterlight in the rear pillar, creating a six light style. The overall proportions and the kicked-up rear wing line were however unmistakably Jaguar. 

Under the skin, the XJ40 featured a new rear suspension with the brake discs mounted outboard. The manual gearbox was a five-speed Getrag 'box, first seen on the XJ-S, while the automatic was a ZF four-speeder with the new shift pattern called the J gate. The interior was brought up to date with better ergonomics, and sophisticated electronics which extended to the smaller instruments with bar type displays, and a multi-function trip computer. 

The new car was an instant success, and Jaguar was hard put to keep up with orders until a second assembly line was opened in 1987. As had been the case with the original XJ6 in 1968, there was for a time a 'black market' in nearly new XJ40s, but by 1989 production had been increased to a record 39,000 cars per year. For the 1990 model year, the 3.6-litre engine was replaced by a 4-litre  version, and some months later the 2.9-litre engine was upgraded to 3.2 litres; in this form, it also received the double overhead camshaft head with four valves per cylinder. As mentioned, the V12 version with the engine now of 6 litres followed in 1993. TWR offered Jaguar Sport versions of first the 3.6-litre and then the 4-litre car, later replaced by Sport versions of the 3.2 and 4-litre models built in-house by Jaguar. On the other hand, the ultimate in luxury was offered by the special-order long wheelbase models which became available from 1993 onwards. 

By the early 1990s, the next new generation of the XJ was under development. An investment of £200 million made by Ford after their takeover of Jaguar in 1989 enabled Jaguar to re-design the XJ40 to make the car simpler to manufacture and improve build quality. The result was the X300, the first of a new generation of Jaguars with a new style of project numbers. For the X300, the opportunity was also taken to re-style the car, the result being called 'retrolutionary' design: Softer shapes and a classic four-headlamp front end were more in tune with the rounded shapes coming back in the 1990s, and happily recalled the styling heritage of classic Jaguars of the past. 

As launched in 1994, the X300 range featured a choice of the 3.2-litre and 4-litre versions of the six cylinder engine, now in a modified form known as the AJ16, while the 6-litre V12 was also available. Most exciting however was the new supercharged version of the 4-litre, fitted to the XJR model. With a top speed of 155mph (250 km/h), it was just as fast as the 12 cylinder car, but had even more spectacular acceleration. As before there were basic XJ6 models, Sport versions and Sovereign models, as well as the traditional Daimlers. In 1995 long wheelbase models were added to the range. 

However, the six and 12 cylinder versions of the X300 were to be the most short-lived of the various XJs to date. Jaguar was working on an all-new engine family, which eventually would embrace both V6 and V8 versions. If we disregard the Daimler engines of the 1960s, this was Jaguar's first V8, although an eight cylinder version of the V12 had been under consideration in the late 1960s. The new V8, known as the AJ8 engine, was launched in 4-litre form in the new XK8 sports car which replaced the XJ-S in 1996, and in the following year the V8 engines also appeared in the X300 (which then became known internally as the X308 range). In the saloon models, there were 3.2-litre, 4-litre and supercharged 4-litre versions of the V8. If there was a little
bit of sadness at the time of the introduction of the V8 engine, it was that it meant good-bye to Jaguar's magnificent V12 which had served the company so well for 25 years. The famous names of XJ6 and XJ12 were finally retired, and Jaguar's prestige car became the XJ8 of today. 

The XJ8 in its various forms, including the Sport model, the Sovereign, the supercharged XJR and the luxurious Daimler, is true to Jaguar's traditions and keeps the marque at the pinnacle of the global prestige car market.