The Jaguar 420 and its Daimler Sovereign equivalent were produced for a short period at the end of the 1960s as the ultimate expression of a series of "compact sporting saloons" offered by Jaguar throughout that decade, all of which shared the same wheelbase. Developed from the Jaguar S-Type, although the S-Type continued to be sold alongside the 420/Sovereign until both types were supplanted by the Jaguar XJ6 late in 1968. The Jaguar 420 should not be confused with the larger Jaguar 420G.
Pedigree
The 420/Sovereign traces its origins back to the Jaguar Mark 2, which was introduced in 1959 and sold through most of the 1960s. The Mark 2 had a live rear axle and was powered by the XK six-cylinder engine first used in the Jaguar XK120 of 1948. The Mark 2 was available in 2.4, 3.4 and 3.8 litre engine capacities.
In 1961 Jaguar launched two new models with the triple SU carburetor version of the 3.8 litre XK engine; the Mark X saloon and the E-Type sports car. Both cars used versions of Jaguar's new independent rear suspension; the Mark X having a 58" track and the E-Type a 50" track. In 1965 the Mark X and E-Type were updated with a new 4.2 litre version of the XK engine, still using triple carburetors.
Meanwhile, in 1963 Jaguar had introduced the Jaguar S-Type as a development of the Mark 2. It used a new intermediate-width 54" version of the independent rear suspension in place of the live rear axle of the Mark 2. Other differences from the Mark 2 were extended rear bodywork to provide for a larger boot, a changed roofline for more rear seat passenger headroom, a slightly plusher interior and detail differences around the nose. The S-Type was available with either 3.4 or 3.8 litre XK engines (only 3.8 litre in USA) but in twin carburetor form because the triple carburetor setup would not readily fit into what was essentially still the Mark 2 engine bay.
In
ref., James Taylor suggests four reasons why Jaguar boss
Sir William Lyons might have decided to add yet another
model to an already extensive Jaguar range, these were:
1.sales of the Mark X were disappointing; the car was widely seen as being too big and cumbersome and a smaller car with similar standards of technical sophistication and luxury he thought could be more successful
2.demands for more luxurious features would add weight to any future models, forcing the drive towards a 4.2 litre engine compact saloon
3.a combination of the 4.2 litre engine with the compact saloon body was expected to have market appeal
4.aesthetic objections to the controversially styled S-Type were known to be harming its sales
Consequently, Sir William initiated development of a new saloon based on the S-Type, retaining its 54" independent rear suspension but adding a twin carburetor version of the 4.2 litre power plant and frontal styling more akin to that of the Mark X. The new car was released in August 1966 in the form of two badge-engineered models, named Jaguar 420 and Daimler Sovereign.
In styling terms, the 420/Sovereign was essentially an S-Type with that car's curvaceous nose made much more linear, the better to match its rear styling (which was not altered). Contouring around its four headlamps was relatively subtle, with small peaks over each, and its flat frontage sloped forward slightly. The square grille with central divider matched that of the 420G, (which was the new name given to the Mark X at the time of the 420/Sovereign's release). The fog lamps of the Mark 2 and S-Type were dropped and dummy horn grilles were added below each inner headlamp to break up what would otherwise have been a large expanse of flat metal on either side of the grille. The tops of the front wheel arches were flattened to match the squarer lines of the nose. The slim line bumpers dispensed with the centre dip which had characterized the bumpers of the Mark 2 and S-Type. All this was done to improve the car's aesthetic balance compared with the S-Type and to create a family resemblance to the Mark X/420G, changes which Sir William could not afford (in either time or money) when the S-Type was designed. No attempt was made to give the 420/Sovereign the same front-hinged bonnet as the Mark X/420G and it retained a rear-hinged bonnet of similar dimensions to those of the S-Type and Mark 2.
Changes to the S-Type's interior to create the 420/Sovereign were driven mainly by safety considerations, with the wood cappings on the doors and dashboard replaced with padded Rexine and a wooden garnish rail on the tops of the door linings. The adoption of an electric tachometer meant that the cabin clock was relocated from there to the centre of the dashboard top rail, where it was powered by its own battery. The S-Type's pull out map tray below the central instrument panel was not carried over to the 420, although the 420 retained the same central console and under-dash parcel tray. The seats of the 420 were of slightly different proportions to the S-Type, although they appeared very similar.
The factory-quoted horsepower rating of 245 bhp (183 kW; 248 PS) was measured using the SAE (gross) system current in the USA at the time the 420/Sovereign was sold there. The SAE (gross) system excluded many accessory drives and often used non-standard induction and exhaust systems and so was replaced by the more accurate SAE (net) system in 1972, long after the 420/Sovereign had gone out of production. Reference states that the DIN horsepower rating of the 1977 USA specification 4.2 litre Series II XJ6 was equivalent to 180bhp. The DIN system yields horsepower ratings which, for most technical purposes, are the same as those that would be obtained using the SAE (net) system. However, the 1977 test would have included power sapping emissions equipment not present on the 420/Sovereign. Therefore, the SAE (net) power rating of the 420/Sovereign must have lain somewhere between 180bhp and 245bhp.
A novel mechanical feature that the 420/Sovereign shared with the 420G was Marles Varamatic power steering, which was offered as an option on the 420 but was standard on the Sovereign. Built by Adwest Engineering Co Ltd of Reading, England, it was a "cam and roller" system in which the non-constant pitch of the cam resulted in a variable steering ratio, with the lowest gearing being at the straight ahead, rising rapidly to either lock. The rise in gearing (equivalent to a drop in ratio from 21.6:1 to 13:1) occurred almost entirely within the first half turn of the steering wheel from the straight ahead position. The effect was to give very light and relaxed steering at the straight ahead, with quick reaction when cornering. There was no adjustment in the behavior of the steering in reaction to road speed. A very few of the last S-Types were similarly equipped.