History Repeating: XJ40 Part 4

Phase Two – 1976-1980: Fortress Jaguar. With engineering the last beacon of resistance, XJ40 becomes its talisman.

Production lines at Browns Lane – image: Birmingham Mail

1975 saw the broken remains of Jaguar in lockdown. Bob Knight’s policy of civil disobedience stemmed the tide of assimilation to some extent, but BL’s operating committees remained undeterred. Like most of the industry, they believed the collapse of luxury car sales in the post-oil shock era would be permanent. The prevailing view was that Jaguar were producing dinosaurs.
Yet despite the daily battles, Bob Knight maintained a semblance of an engineering programme. Foremost was maintaining the current model’s appeal in the marketplace. Work also commenced on a comprehensive styling revision of the existing XJ saloon, actioned in light of growing uncertainty over XJ40’s début. Both Pininfarina and Bertone were engaged to provide proposals for revisions to the canopy section, aimed at improving rear headroom and a more contemporary silhouette. Work on this would continue, culminating in the 1979 Series III.

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Jaguar’s incomparable 5.3-litre V12. Image unknown

Meanwhile in the seclusion of Knight’s engineering bunker, XJ40’s mechanical specification was fleshed out. In the wake of the fuel crisis, Jaguar’s V12 engine was viewed as commercially moribund; customers baulking at its 11-mpg thirst. Engineers left few stones unturned: two-speed axles, 8-stroke variable cylinder engines, a 24-valve 3.8 litre XK unit; all of which came to little in the search for efficiency. Earlier in the decade, a 60° V8 was derived from the V12 unit, but its inherent deficiencies saw development abandoned. BL management recommended Jaguar adapt the Rover V8, but once again, ingenuity and guile won the day; Jim Randle reporting back that in order to achieve this, existing work on XJ40’s structure would have to be started afresh. An assertion that was unchallenged.

AJ-6 cutaway in 3.6-litre 24-valve form. Image unknown

The only solution palatable to Jaguar engineers was a new in-house power plant, dubbed AJ6. Inspired from an earlier proposal to halve the existing V12 lengthwise, it would be an all-aluminium, slant-six unit. Weight targets aimed for a hefty saving over the cast iron XK engine and a reduction in capacity to around 3.5 litres. Following experiments with an experimental 24-valve XK unit, it was decided to develop AJ6 initially in two capacities, with alternate cylinder head configurations to allow for alternative marketing requirements. Designed from the outset with two and four valve cylinder heads, it was future-proofed to underpin an entire generation of new, more fuel-efficient cars.

The proposed entry level 2.9 litre power unit would use a single overhead camshaft, utilising the cylinder head design being engineered for the revised ‘High Efficiency’ V12 engine, while the larger 3.6 litre engine would employ twin overhead camshafts operating 24 valves for improved breathing and power. The decision to use AJ6 exclusively would have repercussions later in the programme, but at the time it appeared inconceivable the V12 unit had a future. Fundamentally though, the central thrust of AJ6 was to boot the prospect of the Rover V8 firmly out of the stadium.

Knight later told journalists his engineers experimented with most forms of spring/damper systems, but in the end opted for an evolution of existing practice of all round double wishbones. While front suspension would be similar to existing cars, the rear would be totally new. Mounted directly to the body, it echoed a concept they’d been forced to abandon on the original XJ, promising notable improvements in secondary ride characteristics. Knight’s original design dated back to the late 1950’s and it was something of a surprise it continued to work so well. Knight burned to replace it with something more sophisticated, determined XJ40 would eclipse its predecessor in ride, handling and refinement.

Meanwhile, the 1975 UK motor show that marked the belated début of the XJ-S was also notable in that Jaguar was no longer represented on its own stand, being forced to mix with the Allegros and Marina’s. The implications were there for all to see.

Jaguar’s 1975 offerings – image: Chicago Auto Show


©Driven to Write. All rights reserved. This article may not be copied, republished (in full or in part) or used in any form without the written permission of the author.

Author: Eóin Doyle

Founding Editor. [Dis]content Provider.

1 thought on “History Repeating: XJ40 Part 4”

  1. What did they do for months at end at Brown´s Lane? There must have been periods when it was simply impossible to get any development work done because there was either no direction or the direction was impossible to follow.
    This story really shows the dangers of corporate mergers. It´s extreme but a similar kind of civil war occurs when insitutions in, say, universities are merged. And taking a historical view, the merger of Sicily into the united Italy involved similar clashes of culture.
    It is astonishing any kind of car emerged from this dog´s mess of politics and economics.

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