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Jaguar MKX

Jaguar MKX Published: 1st Jun 2018 - 0 Comments - Be the first, contribute now!

Fast Facts

  • Best model: 4.2 manual/overdrive
  • Worst model: 3.8 automatic
  • Budget buy: Any decent one and DSs
  • OK for unleaded?: Usually yes
  • Will it fit in the garage? (mm): L5232xW1930
  • Spares situation: Not as good as Mk2 or S-type
  • DIY ease?: Ok, but really heavy-duty
  • Club support: Good
  • Appreciating asset?: Starting to be
  • Good buy or good-bye?: They say size matters…
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Once overlooked Jaguar saloon that’s now finding deserved favour. Almost four-door E-type that’s as good as a XJ6 and superior to a Rolls although hard to restore as some parts are specific. A future classic that’s big on everything

Even by Jaguar standards, 1961 was a very special year – but the E-type wasn’t the only wholly new design to leave the Browns Lane factory. The MkX saloon was, in effect, the saloon offshoot as it used the same (triple carb) tune engines and that legendary rear suspension design, wrapped up in a body which was just as sleek and head turning as any sports car.

Yet, the MkX was, until lately, always seen as a bit of a dud. Too large, too heavy, too thirsty and, not least, too brash and flash, for many tastes the MkX’s many hidden qualities were subsequently overlooked for decades and they became bangers: brilliant bargains but bangers all the same.

Thankfully, this is another Coventry cat that’s enjoying a new life – not least because this Transit-sized two tonner is not so big anymore and many of today’s people carriers dwarf this virtual 17ft (6ft 4in broad) cruise liner; the new F-type is actually four inches the wider…

The Jag’s sheer size, style and stance was dictated by the all important American market it was squarely aimed at, although poor sales both sides of the pond saw the fat cat ‘killed’ off by 1970, although the basics of the MkX lived on in the Daimler DS420 right up to 1992 and this certainly helps in terms of spares and repairs.

Next year, the XJ6 celebrates its 50th birthday. A landmark in saloon design, yet it owes a lot to the MkX, where some say it’s as good if not better and certainly a nicer car to travel in and drive than a Rolls of that period. Want this Gigantic Jag instead?


1961 Aimed squarely at the lucrative US market, the MkX was introduced that October and was as radical as the E-type.

Mechanically. it used a good percentage of E-type in its make up, including those famed XK engines and that legendary independent rear suspension clothed in a stylish 17ft body although, despite being of monocoque construction, it actually weighed almost 200lb more than the old chassis-framed MkIX! Options included, overdrive, automatic (as most were) and power windows but power steering – thankfully – was standard.

1964 Along with the E-type, the MkX gained the torquier 4.2-litre engine (with an alternator) together with a better, slicker Jaguar-designed all-synchro gearbox, either with or without overdrive. A variable-rate Varamatic power steering system in place of the original, lifeless, PAS set up was fitted (also for S-type and 420). The heater set up is improved (air con surfaced two years later).

1965 Limousine derivates launched complete with passenger division glass and cocktail cabinet; less than 50 were built.

1966 The big cat’s last revamp as Jaguar’s flagship was revised and rebadged as the 420G although the changes were mainly trim and details, such as special perforated leather seat trim and a safety padded dash top. Externally, there are new style hubcaps and grille plus optional two tone paint. Again, a limousine variant was made but only 24 were produced. MkX 4.2 officially was discontinued in December so the pair were produced in tandem for a few months.

1970 Apart from changes to the engine mountings in 1967, and XJ6 brake servos for ’69, the car survived until 1970 after only 25,212 were made; a third RHD. Per annum it was lowest selling Jaguar ever but one inescapable fact, however, is that the car shared the same showroom floor with the XJ6 for almost two years and because the latter was in such short supply, to begin with, many buyers chose the 420G instead, causing it to survive until June 1970 with some even making a J-registration plate.

The 420G soldiered on as a coach build until 1992 and around this time specialist Craig Hinton also produced a dozen two-door cabriolets, such was the strength of the standard body construction.

Why this Coventry Cat failed to find homes in the States is strange but has been put down to two major reasons: the car looked too American for US Jag fans, and, secondly, lacked the grunt of a V8 which Yanks love. Ironically, this point could have been addressed very easily with the Daimler 4.5 V8 that was used in a number of development cars (as was the Jag V12) but politically it was a no-goer; a shame as records show it was a great combination.

Sadly, Jaguar didn’t learn its lessons as when the XJ40 was being designed, the engine bay was deliberately designed so that the fine Rover V8 couldn’t be fitted…

Driving and press comments

Occupying almost 17 feet, weighing in at a massive 37cwt, the MkX is still large car by today’s standards (although a Ford Focus is as wide) but, unlike the modern Ford, the benefits are all inside where rear seat space (along with boot capacity – a Jaguar rarity) is so great, that they almost occupy another post code. This saloon still impresses with its magic carpet ride, quietness (unless the engine is revved hard) and cultured comfort from that old world Jaguar interior.

With so many of today’s drivers used to piloting 4x4s, a MkX is no longer the culture shock it was half a century ago but still you need a decent-sized drive and (preferably double-sized) garage to store one.

With its E-type DNA the MkX drives and handles far better than any other big old classic barge of that era, although it’s no sports car, of course! Also the car’s prowess depends on how good the suspension – and that complex IRS in particular – has been maintained. Even so, it takes a brave soul to hurl a MkX around but with a maximum speed of well over 120mph and a zero to 60 clip in some 10 seconds (3.8 manual, autos are much lazier) it can still surprise many moderns although it goes without saying that the MkX was designed more for upper class cruising, where in its day was better than a compatible Rolls-Royce and on par to our minds, with the much acclaimed XJ6.

Even with those sporty E-type engines employed, performance from this big barge is now at best diesel supermini quick (although the Daimler V8 development ones were reputed to have been astonishingly quick…) and because these engines are worked hard to haul such a bulk around, you can expect little more than 16mpg and probably worse if age and mileage has taken its toll on the engine and fuel system.

Apart from instantly latching on to the lack of engine cylinders, American Road & Track still gave the Jaguar ten out of ten, remarking that “no other car of the size and type gives a better combination of comfort, handling and silence”.

In 1964, after introduction of the Marles Varamatic power steering, Autocar said the steering was “a revelation, giving relaxed high speed control.” Ride comfort was also praised, being “at its most impressive when the car is at speed on a good road,” and “100mph motorway cruising approaches the refinement that goes with modern air travel.”

Well over half a century on Classic Motoring regular columnist Stuart Bladon (ex-Autocar tester) remembers the Jag’s roadholding also earned praise, and this was unwittingly demonstrated when an impatient tester at MIRA was using the only available short straight for the acceleration tests. Repeated heavy braking from 80 or 90mph had the inevitable effect of sudden, complete brake fade, with the pedal going down to the floor. “With commendable presence of mind, the driver warned the co-tester ‘get down, we’re going to spin!” recalls Stuart. Slight of build, passenger Warren Allport needed no second invitation to dive under that mammoth walnut facia, as the driver twirled the steering round onto full lock (thank goodness for PAS-ed!).

“The pair counted how many times the car had spun, but when the smoke cleared they were surprised to find that the car was still on its wheels and the tyres had not deflated! That the car had not rolled paid great tribute to the stability of the Jaguar MkX. It seemed a big car, and the relatively low seating position makes it seem all the wider, but it was a joy to drive. Rear seat passengers enjoyed extravagant legroom,” he recalled to us.

Values and marketplace

The MkX is another of them “if only I’d bought one when they cheap” classics. For decades they were beer money and, until fairly recently, even ten-out-of-ten examples struggled to beat 10 grand. According to some price guides, you can triple or even quadruple this now, although in the real world of hard cash £20,000 is ample to net a good one.

Which one? Well, if info is correct you can’t be too picky as there’s just 50 MkXs registered, 18 SORN but over 100 420G versions. That said, condition and provenance counts the most.


Pragmatic owners wanting to keep their classics stock should still fit certain upgrades such as electronic ignition, a larger, more efficient radiator and, perhaps S3 E-type or DS 420 limo brakes along with (GAZ, Spaz or Koni) dampers and re-bush the IRS (a time consuming and expensive job albeit one that really pays dividends on the way it drives), all of which will make a very nice car indeed.

Few owners will want to make this fat cat a four-door E-type but the principles are similar. The car’s size and weight takes it toll on the suspension and steering and just bringing them up to spec will make a world of difference on the majority of cars before uprating – which will probably spoil the refinement and comfort if you go overboard.

As the DS420 was built on the MkX platform, it effectively means that some of the upgrades can be incorporated into the earlier car, such as superior front brake calipers with their ventilated discs that bolt straight on – and very welcome they are too!

It is also possible to fit the four-speed automatic found in the XJ40 which is a real boon as MkXs are strangely quite low geared even with overdrive. Another way to aid cruising is to swap axle ratios with other models and the one from the E-type S3 V12 (3.07:1) is regarded best all rounder.

If you want a five-speed opt for S3 XJ6 unit as it boasts uprated bearings. While car employed E-type/Mk2 axles, 14inch wheels were fitted to the MkX/420G and for some time the right performance grade of 205 HR x14 (7.50 if crossply) section tyres were hard to obtain, although the situation has improved – try Longstone or Vintage tyres if you want period rubberware. Many use XJ6 rims and swapping over to the XJ6 15inch wheels is worthwhile as it is inexpensive as the 205 VR 70 15 tyres have the same rolling radius as those old ‘balloon’ originals, giving as improved ride and grip without altering the speedometer reading; some 14inch American tyres are also available. We’ve never seen E-type wire wheels fitted, but this doesn’t mean that this swap is not possible.

The MkX is E-type powered, complete with triple (but different) carbs and an inlet manifold design so same tuning principles apply. Up to 300bhp for the road is attainable with head mods and D-type cams – but it’s expensive. A milder best budget alternative is to fit the fuel injected XJ6 S3 head with its cams and (optional) pistons. Ignition needs to be spot on so go electronic and set with strobe or on a rolling road. Daimler V8s and Jag’s own V12 units slot in as do a variety of American engines.

Biggest cat of them all

The MkX didn’t die when the XJ6 came along in 1968 – it morphed into the biggest cat ever, the Daimler DS420, replacing the old stately Daimler Majestic Major with something more modern. One of the most popular limos of them all, it was essentially a stretched 420G (by 21 inches) with a Daimler Sovereign frontal and the hybrid survived in service until 1992. Apart from a bench front seat, the DS drives pretty much like a 420G and can see 110mph from that venerable 4.2-litre XK engine. When new it was some 50 per cent cheaper than a Rolls Phantom as well as being far more comfortable and enjoyable to drive. The DS is the bargain of the big cat family range with good cars going for well under ten grand and as they survived until 1992, you can own modern classic that’s free from the usual old car worries. You can even make this big cat earn its keep at weekends as a wedding car and so on. The downsides? Do you want to look like a funeral director or chauffeur when out on a quiet classic cruise?

What To Look For


  • The XK engine is well known and generally durable. Chief wear points are noisy timing chains, over-silent tappets (meaning that they have closed up in service and require re-shimming – a head off decoke job), overheating and signs of coolant stains around the head, spelling impending gasket failure. If the car has had an uprated radiator, it’s a real plus point.
  • Most old XKs leak oil via a failing rear crank oil seal. It’s rarely serious though and usually highlighted by trying to keep the lube topped up to maximum level. More importantly, see that the oil pressure is a strong 40-45lb on the gauge at 3000rpm with the engine hot, that there’s no smoking from the exhaust, and that the electric auto choke kicks in and out.
  • Later XK engines fit (and may well have been substituted already) but watch the later long stud type which aren’t as long lasting. A good rebuild costs at least £4000. Lower timing chain renewal is a major head and sump off job on all but you may not need to completely remove the engine to do this – but remove the large bonnet to ease access.


  • The Mk 10/420G is a mixture of good and bad news. The former is that, because this fat cat provided the mainframe of the Daimler limousines (such as hearses!) right up until 1992, certain hard parts and panels are still in very reasonable supply even from the manufacturers if price is not important.
  • The bad news is that because these big old Jags were not seen as collectible as values are low, the vast majority are bodged lash-ups that may look good on the outside, but are real liabilities under all that metal (and typically filler!).
  • For spares, look to Mk10 Motor Spares (mk10msm., The Jaguar Mk10 & 420G Owners’ Symposium plus the likes of Martin Robey, SNG Barratt, Rimmer Bros. Just Jags and David Manners.
  • Restoration projects can be had for a few grand but they cost as much as an E-type to rebuild properly while that wonderful wood and leather interior could cost almost double that of a Mk2.
  • n More than 40 bits of matched wood trim made up a Rolls-like cabin and some bits, such as those super picnic tables and centre consoles are particular to the MkX. Happily, a full retrim kit from BAS International is available, but costs some £7500.
  • Those massive bumpers should be scrutinised for damage and corrosion because fettling all that chromework will prove very expensive indeed – almost £800 for a bumper, for example. Don’t rule out using exterior and interior items from a defunct Daimler DS to save money. Vacuum-operated heater controls with twin heater fans were standard and differed from other Jags of that era.

Body and chassis

  • Rust has to be the biggest enemy. Start at the floorpan and work upwards! Look for signs of serious rot and poor repairs on the floor, especially by the front seats, all box sections, chassis legs and diff mounting points, jacking points, radiator vicinity, cross-members, valances and the suspension pick-up points. Expect some bodges on all but the top cats.
  • Despite their size, the front wings appear to last better than other Jags of that period although, the big sills rot badly with the cosmetic outer one (inner rusty ones are much more serious) priced at just under £200 a side from specialist. Ditto the lower half of the rear wings (around £230 for repair sections). Other points to watch include the front and rear aprons, inner wings, boot lid, door bottoms, fuel tanks and that huge bonnet: the latter should also be checked for alignment. DS420 was in service well into the 1990s giving a little more scope for some body parts.

Running gear

  • Transmissions are strong and the optional automatic, of which 90 per cent were, suits the car but if in need of repair can cost over £700. Sluggish operation may simply be adjustment or old fluid. GM400 ’box from later DS420 fits and a good move.
  • With manuals, watch for a slow change, weak synchromesh, noise, lazy overdrives and worn clutches, the latter where replacements aren’t really a DIY proposition. Check limited slip diff for operation and quietness; needs special lubricant. Diff leaks commonly spew lube over the inboard rear brakes.
  • On such a big car expect to find tired springs and dampers. The E-type independent rear end is fitted with a host of bushes and these are prone to wear, meaning the subframe needs to be removed – a major job on the driveway and £1000 at specialist but well worth the investment.
  • Only front wishbones are interchangeable with Mk2. Ball joint and track control arm wear common as are failed bushes and power steering leaks. Keep an eye on the spring pans and mounts for rotting.
  • MkX used a unique brake system with special front callipers; rears are S-type, inboard mounted and parts are scarce and pricey. Rear callipers can seize, especially the handbrake.
  • Kelsey Hayes bellow servo best replaced with later 4.2 or XJ6-types and when sourcing parts, 4.2 had bigger callipers. Superior DS ones from Just Jags sells for a highly reasonable £100, discs £72 a pair.
  • Expect play in the steering, while PAS was never pin sharp anyway and, if defunct (usually accelerated by lack use), perhaps best replaced with a modern electric set up from the likes of Lite Steer and EZ.
  • Odd wheel and tyre size (205 x 14) is hard to source (watch for commercial van tyres fitted instead; okay for the car’s weight, but not for high speeds.

Three Of A Kind

Rolls-Royce Silver Shadow
Rolls-Royce Silver Shadow
Like the Mk10, the Silver Shadow dragged its maker into the 20th Century and today they make exceptional value buys – if you buy a well kept one. Pre ’70 cars can feel sadly ponderous; T2s after ’76 drive the best. Bentley T Series is a somewhat classier option, but all overdose on refinement, craftsmanship and sheer sense of occasion. Specialists, including breakers, contain costs to surprisingly containable levels.
Forerunner to the MkX, the MkVII and MkIX are more stately and stuffy offering unbridled luxury with 50’s dignity. They were far more popular than the MkX when new and today, values are handsomely higher – double the price in some instances. The later big fat cat is much more modern to drive however although, for its era, the earlier versions were also considered pretty sporty.
Aston Martin Lagonda
Aston Martin Lagonda
If you are after a big and brash Brit, then Aston’s square Lagonda is almost the spiritual successor to the MkX. Based upon a stretched DBS platform with V8 grunt and futuristic interior, the Lagonda is as greedy and gaudy as the Jag and values have soared of late. Not cheap to run or maintain and it’s different kettle of camshafts to a normal Aston sports car but there are specialists around to help.


A classic Jaguar… or an oversized fat cat that verges on the vulgar? Possibly the MkX and 420G is a bit of all of them rolled into one sleek saloon. No longer the big fat bargains that they used to be but still a lot of metal for your money. We predict the MkX has a big future ahead of it in the classic world so give one garage room asap but buy the best you can find even if it means breaking the bank. Because making a mangy big cat purr-fect certainly will…

Classic Motoring

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