Engines
No new engines were developed for the S-Type.[2] It was first released with the SU HD-8 twin-carburettor variant of the 3.8-litre XK engine, the same as that which powered the 3.8-litre Mark 2. The 3.8-litre was the only engine offered on S-Types sold into the US market.
The lower powered 3.4-litre S-Type used the same 3.4-litre engine as the Mark 2. It was released a few months after the 3.8S and was not made available at any stage on Jaguar's press demonstrator fleet in the UK. Whereas the 3.4-litre version remained the most popular engine option for the Mark 2, the 3.8-litre S-Type outsold the 3.4 S in the ratio 3 to 2, this despite the 3.8 S being discontinued in mid-1968, a couple of months before the 3.4S.[3]
Mechanical
Despite the S-Type's weight gain of 152 kg over the Mark 2, no changes were deemed necessary to the Dunlop four-wheel disc braking system.
Major changes were made to the S-Type's steering system. The Burman power steering system in the Mark 2, with its 4.3 turns lock-to-lock, was regarded as being excessively low geared and lacking in road feel. In the S-Type it was replaced by a higher-geared Burman unit of 3.5 turns lock-to-lock, which linked the input shaft and hydraulic valve by a torsion spring to improve its "feel".[4]
The heating and ventilating system of the Mark 2 was not considered adequate for the more upmarket S-Type and was replaced with an improved system. Separate control of ventilation direction was provided for both driver and front seat passenger. Warm air could also be directed to the rear passengers through an outlet situated on the propeller shaft tunnel cover between the two front seats.
Suspension
A key element of the Mark X that Jaguar wanted to include in the S-Type was its sophisticated, and by then widely acclaimed, Jaguar independent rear suspension. The suspension was a revelation at the time of its introduction, and remained the benchmark against which others were judged until the 1980s. Essentially a double wishbone setup, it uses the driveshaft as the upper wishbone. It carries the drive, braking, suspension and damping units in a single fabricated steel crossbridge, which is isolated from the bodyshell by rubber blocks. Including this suspension in the S-Type necessitated the development of a new crossbridge suitable for its 54 in track, coming as it did between the 58 in track of the Mark X and 50 in track of the E-Type.
The S-Type used the same subframe mounted, coil sprung, twin wishbone front suspension as the Mark 2.
Styling
Lyons wanted to introduce some of the Mark X's sleeker and sharper lines into the S-Type but with limited time and money available, most effort was applied to restyling the rear bodywork. The S-Type was given extended rear bodywork similar to that on the Mark X, which also gave it a much larger boot than the Mark 2. Relatively minor changes were made to the frontal styling of the car in an attempt to balance the longer rear styling, but the overall effect at the front was still very rounded. The only change made to the center section was to flatten and extend the rear roof line, which made the car look larger and helped to give rear seat passengers slightly more headroom.
The styling of the S-Type was regarded by many of those who worked on it as being not altogether successful. The mismatch between the horizontal lines of its rear styling and the rounded front was least flattering when viewing the car from the front quarter. This ref.[5] quotes Cyril Crouch, assistant chief body engineer at Browns Lane during development of the S-Type, as saying: "'We ourselves appreciated what an ugly looking car it was, and when it came out there was a ... 'Is that the best you can do?' sort of thing! People like myself had to take the stick for producing such an abomination! Perhaps I shouldn't call it that, but I think everyone was very pleased to see the end of the S and move on to the 420. It seemed an odd-looking vehicle.'"The reasonable sales success of the S-Type prior to the release of the Jaguar 420 suggests that not everyone was as offended by its styling as Mr Crouch. Nevertheless, the 420 did "finish the job" in a styling sense by adding to the car a squarer, four-headlamp front end more like that of the Mark X.
The significant styling changes between the Mark II and the S-Type were:[5]
Bodyshell
Starting with the Mark 2's unitary bodyshell, Jaguar's engineers had to alter it to accommodate the independent rear suspension's extra bulk and weight and to extend the rear bodywork. Structural changes at the front were minimal and no changes at all were made to the inner scuttle, windscreen or dashboard structure.
Among the significant structural differences between the Mark 2 and S-Type[5] are: the re-profiled roof line resulted in the B-pillar being approximately 1 in lower and the rear window aperture being larger and more upright; the Mark 2's underbody reinforcing rails were extended to the rear of the car and enclosed, sweeping up and over the space for the rear suspension assembly; the boot floor was double-skinned and ribbed for additional strength; the spare wheel well was relocated centrally in the boot floor (it was on the right in the Mark 2); the lid of the new longer boot was secured by two catches rather than the single catch of the Mark 2; the 12 impgal fuel tank was removed from under the boot floor and replaced by two 7 impgal tanks, one inside each rear wing; new front wings were made to carry the frontal styling changes listed above; new attachment points were made for the new wings and bumpers; and new wheel arches were made to match the new front guards and rear structure.
Interior
The S-Type's interior again reflected the styling of the Mark X but included features particular to the S-Type. Changes to the rear seat accommodation gave the impression of far greater room than in the rear of a Mark 2 and changes to the front of the cabin also gave the impression of greater luxury.
Interior differences between the Mark 2 and S-Type included[5] a scaled-down Mark X burled Belgian walnut veneer dashboard with a burled walnut pull-out map tray below the centre section, the veneer extending to the dashboard centre section, which in the Mark 2 had been covered with black vinyl; a full-width parcel tray was fitted below the dashboard; new controls were provided to go with the improved heating and ventilation system; the front seats were widened to give the appearance of being almost full width, and each was provided with an inboard armrest; the centre console was redesigned to suit the wider front seats and rear compartment heating arrangements; the door trims were given horizontal fluting; Mark X type armrests were added to the front doors along with an elasticated map pocket; the rear doors were given new armrests with a flip-top ashtray and magazine pocket; the front seats were given a new fore and aft adjustment mechanism that raised the rear of the seat as it was moved forwards; the backs of the front seats were made thinner to the benefit of rear seat passenger legroom, and the rear seat had a 50 mm thinner squab and its backrest was more steeply angled, further benefiting headroom already enhanced by the slightly higher rear roof line. These changes did, however, leave longer legged rear seat passengers in a fairly uncomfortable "knee-high" posture.
