FiBoy's XJ12C restoration; rebuilding a Jaguar XJ V12 Coupe

This FiBoy's Jaguar XJ12C homepage is devoted to a restoration or actually a rebuild and modernization of a SII Jaguar XJ 5.3 litre Coupe. Updated 12-huhti-2008

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"Rebuilding a legend"

Only made from 1975 to 1977, the 2-door vinyl topped pillarless coupe was probably one of the best looking touring car made by Jaguar. The XJC's were known as the world's fastest vinyl roof and were unique in their styling and complexity. The 5343cc V12 developed a healthy 285bhp which could propel this glamorous car up to 240 km/h and also allowed it to guzzle petrol at an alarming rate! Acceleration 0-60 MPH was 7.8 s.

After a turbulent two year production run the Jaguar XJ5.3C was dropped from the Jaguar range, less than 2,000 cars had been built. Total production of Jaguar XJC6 and XJC12 models was 10,426.

Jaguar Sovereign (XJ 40) was the replacement of Series III. Undeniably it was a better car - but a bit clumsy because the master designer Sir Lyons was not anymore involved. My S2 XJ could have been a logical evolution of the theme had things gone differently. Actually now it is a Jaguar 6.0L Series 4 V12 Coupe VdP as it has certain Vanden Plas design gimmicks incorporated. Turning it to this condition was a lengthy process but worthy, because now the real super car nature of the Jaguar XJC V-12 becomes eminent. The frontal aspect resembles a great deal that of a modern Bentley Brooklands Coupe!

Actually a real XJ40 coupe prototype exists but that is another story..

The Jaguar 5.3L Coupe that I purchased from Sten in Sweden had 80.000 km on clock and was in fair condition. The original color was Greensand. It was manufactured 10th of January 1975, chassis no. 2G50026BW and first dispatched to Belgium. Still on the original chromed wheels (the same as E-type had).

Solutions to general Jaguar V12 problems found on this site.

The XJ12 C's interior is in moderate shape but a bit tacky. I would have preferred lighter colors in the leather seats over the original Olive shade, especially in a dark car - but the color code in the 70's for XJ sedans came from another planet! The floor mats are Moss green and in good shape.

Had I followed a normal complete renovation route where originality is an issue, the procedure would have been as described here.

More about paint colors and interiors, car pics and practically everything related to the XJ5.3C's, here.

The engine is one of the last carbed units, similar to V-12 E-type. Normally a XJ5.3 has fuel injection. It got new valves, bearings etc at Laatuvaunu, the local Jag specialist. Mechanically the car was quite good. I thought of swapping the carbs to Webers but they were too high. This engine bay of the Jaguar XJC12 is difficult to keep cool and tidy!

Another restoration story and information how the Stromberg carbs are adjusted is found here.

Before I started the XJC5.3 project I used the car daily in order to know what I exactly wanted. As that summer was almost tropical (sic) in Katinkulta, where we spend our holidays, sunroof became one of the desired options although the car had, of course, A/C.

The new registration plates JAG-75 are nicer than the old Swedish ones.

Jaguars are famous for their sweeping lines. The XJC 6/12 got its basic lines from E-type. I wanted slightly beefier stamina; one step bigger shoes and integral fog lights; the originals were an afterthought. In addition, the terrible cheap looking lower grille had to go. Instead, a curved intake was made using the original as starting point. The addition of some sheet metal to the corners eliminated the weakness of the front view.

The original XJ 5.3C Series 2 frontal aspect reminds me of Leyland corporativism - nothing else - no Jaguar feelings. That is why I designed a new, more jaguar than Jaguar nose! Should the lower mesh be chromed as well?

The fog lights to be are Bosch item no 0 305 055 001-730. In the finished car they seem to have been in place for ever!

Present day bolt on wire wheels are so much stronger than original that use even in heavy vehicles is quite OK. Here a 18" wire wheel designed for XK8 is being tested. Pity that the offset was unsuitable. In XJ ser I...III the 17 * 7" rim with 33 ...36 mm offset would be ideal. The bigger wheels caused slight relocation of the carbon canister. Have a look how nice wire wheels look on a mint XJ 5.3C.

The original front wheel arches of the XJ 6/12 are not round, but I wanted them to be. This gives a more balanced looks from all views.

Similarly I desired the XJ12C wheel arches to nicely follow the rubber contours. Using a simple rig the front and rear wheel openings were designed. This treatment in the rear had been impossible with the sedan. The new wheel arches look positively fashionable and Jaguar-like. Big fully visible wheels suit to large cars! Many Jaguar purists will dislike this, but the car is mine! Now they look much sportier and the feedback has only been positive - I like them too!

Every XJ6/12 Jaguar has corrosion in this area due to faulty construction and dynamic stresses coming from the IRS.

I became aware of the need of a bigger renovation when rain water started to collect inside the car in the back seat sink! The drainage tube was clogged and there was a hole to the wheel arch. This is typical to the XJ Coupe models.

The improved construction simply means welding metal between the lower sheet metal and the upper rear seat bottom. The lift point will also get it's share of reinforcing by a bit of pipe. Now the radius arm mount is rigid. The gray color comes from the zinc primer.

The sills were strengthened with heavy gauge (107*2mm) steel pipe. It was fixed to the chassis by spot welding through drilled holes in the inner sill, top and behind. The pipe was fixed to the sill from outside too using a few tags. The sills include new fuel piping too. After this treatment the car stopped flexing! The 2 door chassis was flimsier than that of a XJ sedan - despite of certain original chassis reinforcement. This treatment is similar to what was carried out later to XJS convertibles.

A preheater is being baked into place for future winter use (will get a block heater too).

Because of the sideline, which was widened 15 mm at skirt level only, the end required some beefing up too.

The fuel return solenoid valves used to be in the boot in XJC 12 S2, where they where well protected. SIII Jags had these under the rear wheel valance and hence deteriorated quite fast. I attached them to the rear of check lid where they still are protected.

Another crucial point; the original upper crossbeam serves only as relay stand. This one is additionally strengthened with 6 mm steel vertically and horizontally and most importantly the ends face now also downwards so that two additional nuts can be bolted through the side pillars. This really adds to the torsional strength of the front end of a XJC5.3. When mounting the bar, it was noted that the opening had grown by 5 mm due to car's tilted position without the tie bar - so weak is the front normally!

Although the car has A/C, I thought that a sun roof would be a nice option. Ice cold air can be irritating too on long runs. Jaguar XJ40 Sovereign sunroof was used as a donor like in the Mk1 case. Later it got a headlining made of Alcantara®. The installation of the inner roof was complicated due to the sunroof. With the help of a XJ40 inner roof, which was widened with aluminum sheets, it finally succeeded. The sunroof decreases the available room above your head in XJC12 Series II cars - so for very tall people this is not an option.

The second point were every Series 1/2/3 XJ 6/12 Jaguar shows cracks in paint due to heavy stress, is the area were pillars join the roof. Because of the sunroof, these were opened, thick-walled tubing was inserted and re-welded to yield much stronger pillar

Jaguar sunroof drainage and reinforcement

with a drain pipe continuing all the way down to front wheel arch!

The body work underneath the black vinyl needed attention, so the vinyl was removed. Without it, the car looked so good that I decided not to add any vinyl more. The visible hole in A-pillar will be connected to the fresh air intake in the lamps and to the area where the fans suck the fresh air normally. Through that route I get fresh air into the cabin even if the main intake is covered with snow!

The battery is located in the boot. The main power lead comes in the sill and its corrugated cover is visible here. A power main switch was installed too. It will be accessible through right front tyre aperture. The other side shows the box where the coupe heater is located. The vacuum operated valve is open when there is no vacuum.

Jaguar has stamped recesses suitable to 21 cm Sony loudspeakers. These are 240 W 3-way speakers XS-P2020. I had the same set up in my earlier XJ6 4.2 and it was excellent. The central air outlet was a fine invention in its time but it will probably be changed to the XJ 40 style more refined ventilator outlet. This enables the original use; parcel shelf.

The air flow into the engine bay was improved with fine tuning the air intake by removing unnecessary obstacles from the bonnet. Also underneath the grille aperture, the bent panel edge disturbing the flow was removed. Together with the redesigned lower front part these form an effective air dam to give enough cool air to the hot bloodied beast! Later on the bonnet got aluminum coated insulation.

Inside the wheel arches some louvres were opened into the engine compartment to further improve air flow out of the engine bay. If this is really an under-pressure area as some assume, the system should be effective. Anyhow the problem is getting air out and some Jaguar measures like putting thick foam padding between the gearbox and the body tunnel really counteract this. These louvres really work, they extract hot air from the engine bay quite effectively.

This is what everyone desires, a clean starting point. Sand blasting tends to reveal unforeseen weak areas. In my car they were related to the front end, where rotten metal was revealed. XJ6/12 panels are not as sturdy as in MK7 so extra care is needed when blasting large areas. The right form is easily lost.

This front shock's mounting point is a typical hidden rust spot underneath a good paint. Mechanical stresses cause crazes - the front end of a Series 1/2/3 XJ Jaguar really is in need of strengthening. Some stiffer shocks are unsuitable indeed due to this. Additional strengthening is difficult in this area - one good option might be continuous welding of the seams.

The XJ 12 C gets a epoxy zinc primer + normal red coating on top. The underneath is black, tar-modified epoxy, which does not become as brittle as normal epoxies often do. The car is easy to handle when rolling on such steer-able small wheels.

Jaguar XJ Coupe Sherwood green bodycolor

After Christmas 2002 the XJ12 C finally got it's two component color. In practice it is close to racing green but has metallic undertone. The final color is called Sherwood metallic green.

Gluing the insulation layers starts. Insulation was added to transmission console to the underneath as well in addition to the factory delivered soft foam.

The original XJ12C engine was very thirsty. That's why I decided to go for a modern EFI machine. Here the ECU box is installed into the boot. Note the rear lights and the original bumper with originally front overriders. The battery was installed on a SS tray having drainage to the outside.

The XJ C12 independent rear suspension is based on the original SII carriage but is fine tuned by using the XJ 40 concept with no radius arms. The smaller bushing has found a new life as the lower sway bar link bushing. According to contemporary test results the XJ40 was said to have a better IRS. The reason for this may be that in series 1-3 cars the radius arms caused unwanted rear end steering and these are not needed in the new set-up as the whole carriage is better located to the original mounting points via the new mounting frame.

The mounting frame assembly from XJ40 was cheap because only the diff. and hub carriers are sought after. It was welded to the bottom plate of car's own IRS. The bracket joining the ends of the fulcrum shafts reinforces the linkages and supports the frame too, making the joint quite rigid. There are other more refined methods for locating the back axle, but all of them call for welding mounting points to the body shell and special tubular arms. This method is a straightforward conversion and seems to work.

Underneath we see slight modifications; all piping goes now inside the sills and mounts for the sway bar have been added. The new set up should locate the IRS cage axially so that rear end steering disappears and fast acceleration will not any more twist the rubber joints. The additional mounting points were added for optional A-frame support. They are on the same axis as the rear fulcrum shafts. However, these were not needed.

Jaguar xj40 type rear end in Jaguar XJ12C

The width difference between XJ40 mounting bushings and XJ radius arm bushings was only 7 mm, which was easy to fix with an oval hole for the bigger bushing from the radius arm. This upgrade was easy and straightforward. Original centre silencers will not fit - but they are not needed either when using the TT-extractors.

The XJ40 rear end could have been improved with X-braces where the differential is bolted to, like in Aston Martin Vantage, or by A-frame supports like in many racers but it seems that the XJ40 system really eliminates tram, is simple and quiet too.

Now the fun finally begins! Rear windows work and new seals are partly in place. I am considering to leave out the thin chrome list surrounding the window aperture of my XJC 5.3 to get a cleaner look.

The car has a lot of added electric gadgets due to sunroof, gearbox etc. that asked for another fuse box. Happily enough the new 6litre engine comes as standard equipped with an 120 amp alternator.

I moved the central console 8 cm backwards in order to create an airier cockpit. The old centre parcel tray has disappeared and I am trying to figure it out how to incorporate both a radio and a navigation system into a pleasing newer design. The radio fits above the heater as the air outlet system was changed. The gauges are mounted to the sheet metal and hence inserted into the wood in good old Jaguar style! This necessitated relocation of the smaller gauges to be wider apart from the bigger ones - just to make room for a wood fillet in between. I just wonder might a high tech look suit to old car at all? The final outcome is quite OK!

The engine bay got a new technology multilayer sound proofing. The old one is bolted on to that. This aluminum coated glass-fibre board was used for the bonnet too. These modern materials are pretty efficient - the car got quieter than before.

Everything is ready for the installation of the pre-owned 6 L engine with a 4L80E automatic transmission (from a -95 XJS). This, essentially a GM TH 400 gearbox is a fantastic improvement over all automatic XJ saloon models, which suffer from old fashioned gearing due to those old 3-stage boxes. 4L80E allows fast acceleration if your final drive still giving relaxed cruising at motor way speeds with reasonable mpg. Many XJ powertrain conversions constitute installation of 5-speed manuals. I think that the internal overdrive makes the driving so relaxed, with lots of grunt when needed, that a manual gearbox would be a step backwards.

The 6l engine is finally there! Despite of the longer length it fitted to original mounting holes! This is one of the joys of working with classic Jaguars! In addition to improved performance and fuel economy the looks are so much enhanced over the original carbed XJ 5.3 Litre. New cold air 3" intake is in this photo under fabrication. It works very well because of the correct air dam, the revised nose. My air temperature sensor shows that the incoming air is not heated. The flow area is much bigger in this version compared to the original cold air intakes of the XJ 5.3C.

See and listen to the V-12 purring!

The elimination of the mechanical fan & water pump leads to 2 necessary belts only. By moving the small compressor a bit forward, it aligned with the PAS pump and hence a slightly shorter belt was used to couple them. The hot water circulation pipe is eliminated. Instead there is a pipe connecting the old thermostat housings leading to the radiator's right corner. Radiator is modified to one pass type. The new water piping is relatively small bore to avoid local overheating in the block. The new electric water pump is underneath the PAS pump. The old impeller was removed and a block heater takes the place. The plugged water outlets will receive the transducers for the electric fan (B-bank) and the adjustable pump control module (A-bank).

The engine cooling was further improved with the use of 16" Kenlowe electric fan and an additional gearbox oil cooler, which unloads a lot of heat from the radiator. These cooling devices are controlled independently; Kenlowe fan has an own adjustable thermostat and the aux. fan is controlled by the temperature switch in the suction side of cooling water. The only interlock is from this fan; when it runs also the water pump does at full speed. Now the heat soak will definitively be eliminated. Without the simultaneous water circulation the time needed to cool the engine after parking might drain the battery, now it takes only 5 minutes after a hard drive!

The use of an electrically controlled water pump without thermostats can lead to problems in heater performance in cold climates. Therefore a small electric pump was installed to suck water from both banks and pump it through the heater core to the expansion tank. The 6L water rail facilitates the addition of an extra water nipple needed to the bank B. Because the pump forms the highest point in the system it got an air evacuation nipple too. The pump works only when the heat is on, controlled by an additional vacuum solenoid and a switch in the Series 2 dash.

Tuned "TT" extractors are said to improve the torque. The sound delivered is very nice and the noise level did not increase even though the middle silencers were omitted!. The only drawback is that the system decreases the free ride height. I used Thermo-Tec exhaust insulating wrap in order to reduce under bonnet temperatures and noise. The black coating seals the pores allowing less penetration of liquids. The rear end of the exhaust system is also SS, made by Falcon.

The XJ12 engine bay became a lot tidier compared to the original "plumber's nightmare" design, which actually also had cold air intakes. The engine cover comes from Joe Bergman . New electrical wiring can be difficult due to limited routes to the cabin. I used additional Series II connectors as well the route through the brake servo! The battery (Optima, there is a second one in the trunk!) cooling fan was kept although being superfluous - but it's cool!

Karaasi did an excellent job when stitching the redesigned centre console and the new upholstery to the seats. The Oatmeal colored leather comes from Wollsdorf-Leder. The seat center pleats have perforated leather for improving the ventilation. The console dash was made of sheet metal and actually is quite complicated. The technique for gluing wood veneer onto metal was as follows; first a tough veneer like birch was glued with PUR body glue to the metal. Then the brittle walnut could be glued in moist state using normal wood glues. New burl was added to the doors as well.

The modified dash of the XJ 12 with inserted dials and the modified console are very Jaguar like. It waits to be seen when I find a pleasing Navigator/Radio - system to fit into slots reserved. The hand rest aperture is reserved for the garage opener and mobile phone. New switches are needed for A/C clutch override, small heater pump (includes heater block override, aux. fan override and heated seats. The burl theme starts from the rear seats and ends up to the captain's roof lamps. The front loudspeakers are 6.5" Alpines that still fitted to original slots. As seen, I used the original mats because nice looking original style Furflex is not available.

The doors got SIII door handles because the SII push button construction is hopeless in the winter. Due to the inclination it keeps on freezing. Turn signal repeaters are from X300 and they replace the SII Jaguar emblems that actually did not fit the pure lines of the car. The mirrors look smaller in body colour. The mirror glasses come from XJ40 because they are heated. The final looks with Pirelli 245/55-17" on custom wheels is quite impressive. These rather wide tyres would not have fitted into original wheel arches. The 55 profile gives still adequate ride quality and do not look too flat. The car's profile is decent with original Kent alloys too. The 215/65-15" sized Nokian's Hakkapeliitta 4 winter tyres are just excellent.

As I do not have the courage/skills to enter curves at pace the cat is capable of, I asked my friend Markku, who is a S-type owner and accomplished track driver, to give the verdict at Ahvenisto racing circuit. According to him the Jaguar Coupe is at least as good or better to drive than the new S-type and is really fast. The suspension is in excellent balance and the car heads to where the driver wants. No tendency to under-driving nor does the rear end offer too eager slides. The LSD, tire width and the 7/8" rear sway bar match. The camber is set to 1° negative and the 245 wide tyres give phenomenal grip. As Markku said: "Better brakes and 500 kg off the weight and you will have a track car!" Interestingly a XJ40 with standard tires spinned at this curve at lower speed than the XJ12C with similar but not the same IRS. After the test run the front and rear tyres were at approximately same temperature, which also is a sign of good balance.

The rebuilt classic Jaguar was present at Lepaa British car meeting. The paint changes its hues a lot depending on nearby colours!

Nothing beats the lake side in summer time in Finland. Especially when you can sit down and relax! The vehicle looks almost blue in this pic but that is due to the blue sky and fresh lake water. Compare the colour to the photos above!

The rear side view of the Jaguar XJ 12C is one of the most beautiful of it's kind. Unsurpassed original car design! The slightly modified rear wheel arches look quite original, don't they? The Series 3 type rear lamps and the boot plinth please my I eye more than the original. Compare this to the newer design! The tail is so proportionally designed that people enjoy driving behind!

The rear end is more pleasing now compared to the original looks. SeriesIII backlights and new plinths make up an airier feeling together with original European style Series II bumpers. Straight exhaust pipes a'la Series I had looked nicer but they may retract exhaust fumes into the cabin.

The Series 1 tail was neat and uncluttered. The Series 2 design was clearly inferior in looks and to my mind the Daimler or Vanden Plas design was from the beginning (S1) just right - one should not heel a healthy man!

The modernized front is clearly more aggressive than the original. Doubled dip beams are allowed in Finland for cars manufactured before 1980. The park lights are in the main lamps giving neater overall look. The side view shows the upfront nose. The front is clearly an ancestor to newer designs. Airflow to the engine is greatly improved. I installed headlamp jet washers too. The tiny plug on the right is for the block heater, actually it is fitted to the front cold water hose in normal V12 installations - not to the block.

New mesh grille was manufactured using S3 frame and chromed mesh. The nice Jaguar S2 V12 plinth was kept. The mascot came from Jaguar 420 as well as the bonnet list. Even two Jaguars like it this way! The final outcome is quite different to the original seen on this 5.3l XJC-12.

The Jaguar Series2 grille was not typical to Jaguar as it was slotted horizontally. The matching SII Daimler was better. The Jaguar S3 theme was again an improvement. Nothing beats, however, the classic Vanden Plas smile . Think about these fantastic noses in regard with current styling ideas - pure retro! Contemporary Jaguars tend to have mesh grilles. A truly modern Jaguar Coupe could look something like this design study. There will always be a market for sleek and fast coupes, this is also evidenced by the launch of Mercedes CLS 350 series, which carries some Jaguar styling items.

Targeted XJ12 Series IV 6 L Coupe specifications in short

V12 6 litre engine + 4L80E - automatic gearbox + modified cold air inlets and cooling air outlets

AJ6 High Torque Inlet Manifold + remapped ECU chipset tuning + "TT" extractors

Davies Craig Electric water pumps and Kenlowe cooling fan + one pass radiator + oil cooler

Heavy duty front springs + 1" GTJ sway bar, Konis

GTJ Upgraded rear springs + 7/8" sway bar, Konis

Rear IRS with XJ40 type carriage location, 3.7 final drive

245/55-17" tyres on KAE17_11 spoke custom wheels, modified wheel arches

Air conditioning, Electric windows + and Sunroof, Central locking + theft immobilizer

Heated seats, mirrors and backlight. Block & cabin heaters needed in Finland

Upgraded Radio + Navigation system. Five loudspeakers with CD changer in boot

Stiffened, widened body painted with Jaguar's Sherwood Green Metallic - color.

Redesigned car front; new grille & integral fog lamps, modified dash and console, Fiboy's designs

If you have questions about the car, please have a look on the Introduction - page, where my contact information is.

Introduction
XJ12C Rebuild
Mk1 Remanufacture
MkVII Restoration
XK120 Renovation
Family&Friends
Links

Other XJC links: For other links see the links page

Mohr House

Jaguar Legend

XJ6 Coupe.nl

If you have got a related website, pls contact me!