Although it is eleven years since the XJ6 was introduced, the Jaguar/Daimler model range remains unsurpassed in its combination of ride comfort, suppression of road, suspension and wind noise and roadholding. How could Bob Knight and his team of engineers improve on this near perfection? The answer has been to make the coachwork itself more refined whilst leaving the chassis practically unchanged save for fitting stiffer steering rack mounts to improve response when turning into a corner. In the case of the 4.2-litre car, the adoption of fuel injection has put back the performance which increased weight and restrictive emission regulations had sapped away over the years and a five speed manual gearbox is available for those customers who want a more sporting alternative to the Borg-Warner Model 65 automatic transmission on the XJ6 3.4 and XJ6 4.2.
At a quick glance the new Series III is not all that different to the Series II, the most obvious change being the wrap-around bumper bars clad with black injection mouldings. Closer examination reveals that the profile of the “glass-house” area above the waistline is completely new. At the rear the roof has been heightened to give passengers more headroom, so important in a car which is often chauffeur-driven. As a result the roof is less rounded and more angular when viewed from the side and the roof-line sharper. The backlight is flatter, yet generous parcel shelf space remains. The screen pillars are raked three inches further forwards so that the higher roofline actually looks sleeker than the original shape. Increased tumble-home of the side-windows has been created by reducing the width of the roof. Deeper windows all round have considerably increased the glass area. The front quarterlight pillars have been removed. Standard equipment laminated windscreens are fitted by direct glazing, which has an added bonus of increasing bodyshell torsional strength. Tinted glass is standard on all models except the 3.4, on which it is an optional extra.
Another obvious external change on the Jaguars is a new radiator grille with vertical bars and a centre rib, shared by both the XJ6 and XJ12; the latter has lost its central “V” badge and is distinguished merely by having a gold on bronze Jaguar head mascot at the top of the grille instead of the XJ6’s gold on black. Daimler grilles are unchanged. Door handles are lift-up and flush fitting, revised rear lamp clusters incorporate reversing lights and a flatter, wider number plate light housing incorporates the boot lift latch. Large, door-mounted, twin exterior mirrors, available with either electric or manual remote control, are a standard fitment. I thought the new black and stainless steel wheel trims of the XJ6 we tested as attractive as the optional alloy wheels fitted to “our” XJ12.
Those then are the obvious differences. General equipment has been considerably improved too, but more of that later. First let me deal with the revised mechanical details of the XJ6 4.2, the most significant change in this new range. Over lunch Bob Knight and Harry Mundy made no bones about their concern and awareness during the run of the Series II 4.2 that its performance had begun to be sadly lacking. Indeed at one stage its power output had dropped below 170 b.h.p., within a handful of b.h.p. of the 3,442 c.c. engine, which continues unchanged in Series III form, producing 162 b.h.p. DIN at 5,250 r.p.m. Mundy’s modifications have given the 4,235 c.c. engine an enormous boost to 205 b.h.p. DIN at 5,000 r.p.m. to set this model well apart from the bottom of the range car.
Ironically, after the emasculation of Jaguar power by emission controls, this big improvement results from the use of an engine developed to comply with US emission regulations and which has been fitted to Series II US cars for a little while. Its main feature is the fitment of Lucas-Bosch electronic fuel injection, a joint Jaguar and Lucas development of the K-Jetronic system. A single high pressure pump fed from the twin fuel tanks maintains a constant 36 p.s.i. pressure to the injectors relative to the intake manifold pressure. The heart of the system is an electronic control unit connected to sensors on the engine. Fuel injection pulses are triggered from the Lucas Opus electronic ignition system and are produced every revolution instead of every cycle as on the D-Jetronic system used on the V12 engine. A separate automatic cold start circuit is incorporated. A special economy feature on 4.2-litre cars with automatic gearboxes is an overrun fuel cut-off which stops the fuel supply to the engine when the throttle is released until revs drop to 1,200 r.p.m.
Other improvements to performance have been brought about by raising the compression ratio to 8.7:1 and fitting larger 1.875 in. inlet valves. Induction noise has been reduced by removing the hot air flap in the air cleaner which was necessary for carburettor fuel control.
GM 400 automatic transmission is standard equipment on all XJ12 5.3-litre Series III cars and the majority of the 3.4-litre and 4.2-litre cars will be fitted with Borg-Warner Model 65 automatic transmission, compulsorily on the Daimler Vanden Plas 4.2. For the majority of Jaguar-Daimler owners who prefer manual transmission (only 10 per cent at the last count), Harry Mundy and his men have developed a version of the Rover 3500 five-speed gearbox to replace the four-speed overdrive unit previously fitted. Incidentally, an announcement last year that the five-speed ‘box had been made available on the Series II was premature. Modifications required to make the ‘box stand up to the extra demands of the Jaguar power included the bigger Timken bearings and a stiffer tailshaft. Jaguar designed their own, shorter shift gearchange mechanism too, which is machined at Radford, shipped to Pengam in Wales for assembly on to the gearbox and then shipped back to Radford to be mated to the power unit. Mundy insisted on having a lift-up reverse protection instead of knock-over – anybody who has felt the ease with which well-used earlier Jaguar gearboxes, particularly pre-synchro units, could be slipped into reverse inadvertently will realise why. Both manual and automatic 4.2s will have 3.31:1 final drive ratio against the low 3.54:1 fitted in later series II cars and the latest 3.4.
With this new gearbox comes a new hydraulic clutch release system, a hydrostatic arrangement in which the lines are always full and under slight pressure, so that the thrust race is always lightly in touch. The old carbon thrust washer has bitten the dust at last.
Coincidentally with the arrival of this new model, Jaguar have adopted a totally revised paint finishing operation, carried out in a new paint shop alongside the Pressed Steel body build plant at Castle Bromwich. The new process involves the use of ICI thermoplastic acrylic paint, of which four coats are applied automatically after more thorough preparation than previously. This TPA is baked at much higher temperatures than the old paint finish and is claimed to give a better, more even, harder yet flexible finish. The bodies are final-finished before delivery to Browns Lane for assembly instead of receiving their final spray coat after assembly and road testing. Each car continues to be individually road tested, however. All Series III inner panels, the longitudinal chassis members and the doors are wax injected for corrosion protection.
With this new paint process comes a much wider choice of colours. Nine high-gloss colours, plus black, will be progressively introduced, with the identifying point of a single coach-line on the 4.2, a double coach-line on the 5.3 models. Five metallic colours will be offered: apart from silver, metallic colours were dropped from the XJ range early in its life because of problems with them. XJ-S coupes will also utilise the new paint process.
Driving the Series III Jaguars
Andrew Whyte first of all proffered the keys of a Jaguar XJ12 5.3 (this is the full nomenclature on the Series III boot-lid). It is almost impossible to be subjective about a car which was so very nearly perfect when we tested it in earlier guise. Sensitive instruments might detect that this latest V12 is quieter than the previous model, for all the Series III cars have improved sound deadening, but when the quietest car in the World is made quieter still, the human car can barely tell the difference. The only obvious wind noise came from the twin, electrically-adjustable door mirrors.
The immediate impression was of a lighter, airier, less claustrophobic cockpit, with much improved all-round visibility and mirror vision. The somewhat reflective veneered facia and instruments are unchanged. The so-comfortable front-seats in all the models have lumbar support adjustment over a range of 1½ in. Both W. B. and I felt the seating position to be a little low, especially now that the increased headroom allows more latitude. Electrically controlled drivers’ seats, incorporating height adjustment, are available as an extra. Both front seats on the Vanden Plas models have electric control as standard.
At last Jaguar have fitted self-parking wipers to their saloons, the column stalk also offering intermittent wiping.
With a car so smooth and quiet as this 287 b.h.p. V12 Jaguar, even the most cautious drivers can slip unwittingly to very considerably over the speed limit. Econocruise speed control, fitted to the test 5.3, is a very welcome optional extra on this model and the 4.2 automatic. It is switched on by a rocker switch on the facia and set at the required speed by a very awkward-to-operate button in the left hand steering column stalk. The setting can be over-ridden by throttle or brakes and the set speed resumed by pressing the central rocker switch. It works smoothly and efficiently, though not so conveniently as the single-stalk Porsche cruise control.
This 5.3 pulled an indicated 100 m.p.h. at 4,000 r.p.m. in virtual silence and its astonishing acceleration on full kickdown was accompanied by a modest volume whirring from under-bonnet.
The steering was creamily effortless – many would say overlight – yet positive enough and responsive. It employs the seven-tooth rack as before on the later V12s and XJ-Ss and this higher steering ratio has now been adopted for the six-cylinder Series III cars.
There is not much more I can add to what W. B. has said about our brief drive in the XJ12 5.3, a sublime way to travel which we have experienced and written about before. The 5-speed manual XJ6 4.2 was more interesting, almost a return to a real Jaguar sports saloon, only slightly less hushed than the V12 and with quite vivid performance compared to the earlier 4.2.
The extra power, improved throttle response and better control through the well-spaced gear ratios gave the impression through both performance and handling that this Series III had lost half a ton in weight. W. B. has already described the extraordinary flexibility of this long-stoke “six”, which matched the Rover Turbo tested elsewhere in this issue in its refusel to stall in fifth gear, though there was a detonation when the throttle was floored.
The gearchange of this low-mileage car was still loosening off, but its positive, shorter movements were preferable to those of the Rover 3500 and my only real criticism was of the closeness of the central console, which my elbow caught during quick cog-swaps. Clutch action and sensitivity was a great improvement over the heavy, dead-feeling mechanism of old.
The more I drove this middle-sized manual Jaguar the more I liked its excellent performance, roadholding which remains second to none in in field, first class brakes and the lightness of its handling. All this accompanied by unbeatable comfort of ride, and whispering progress. No doubt about it, these latest improvements have converted what had become a stodgy fine car into a lively fine car.
A few other details worth mentioning is that electric windows, central locking, interior light delay, a timed heated rear window as on Mercedes, an electric aerial delay to stop it whirring up and down every time the starter key is turned, halogen headlights and radio/stereo cassette are all included in the package. Extras available include headlamp wash/wipe, all electrically operated sun-roof and air-conditioning (standard in the Vanden Plas). – C. R.