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Jaguar XJ12 SI
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Gearbox
The Borg Warner automatic gearbox suited quite well the nature of this engine, for what was initially intended by Jaguar; smooth ride, minimum effort for the driver. With three speeds available, it was deemed adequate for the immense torque the V12 generates, especially at low range, with a torque converter taking all the fuss away.
Still, having read how in the Seventies you could start an XJ-S, engage fourth gear and pull from standstill to maximum speed in less than a minute, I was gob smacked! I also wanted a manual gearbox on mine, do what Jaguar never produced, a manual XJ12!
After taking to my friend Jim Bolton, he came up trumps with a XJ6 manual overdrive box coupled with an E type SIII V12 bell housing and a XJ6 pedal box. All these items were fitted in a scrap metallic blue XJ12 SI that Jim dismantled; someone had modified this Jaguar in the past along the lines of my project. I got a feeling it might have a been a Guy Salmon's Jaguar. An old chap, Terry Mears, who worked for many years in the industry, informed me that was quite usual for Guy Salmon to modify his cars, adding unusual features and usually painting his projects in metallic blue. If you know better, please do let me know!
The hunt was now for a gearbox tunnel cover, in order to clear the box linkages and lever. Chris Coleman managed to unearth one from all his parts and it only required minimal trimming to the opening in order to clear the lever when engaging reverse. It was promptly sand blasted and powder coated in black. New Jaguar rubber gaiter and knob from an E-type were bought from SNG Barratt.
Still, having read how in the Seventies you could start an XJ-S, engage fourth gear and pull from standstill to maximum speed in less than a minute, I was gob smacked! I also wanted a manual gearbox on mine, do what Jaguar never produced, a manual XJ12!
After taking to my friend Jim Bolton, he came up trumps with a XJ6 manual overdrive box coupled with an E type SIII V12 bell housing and a XJ6 pedal box. All these items were fitted in a scrap metallic blue XJ12 SI that Jim dismantled; someone had modified this Jaguar in the past along the lines of my project. I got a feeling it might have a been a Guy Salmon's Jaguar. An old chap, Terry Mears, who worked for many years in the industry, informed me that was quite usual for Guy Salmon to modify his cars, adding unusual features and usually painting his projects in metallic blue. If you know better, please do let me know!
The hunt was now for a gearbox tunnel cover, in order to clear the box linkages and lever. Chris Coleman managed to unearth one from all his parts and it only required minimal trimming to the opening in order to clear the lever when engaging reverse. It was promptly sand blasted and powder coated in black. New Jaguar rubber gaiter and knob from an E-type were bought from SNG Barratt.
Chris did manage to find me a gearbox supporting frame but unfortunately it must have been from another earlier Jaguar saloon. Still, luck was on my side as the automatic box frame fitted perfectly as did the prop shaft! No changes or modification were required.
I always knew one reason Jaguar didn't fit an Overdrive to its V12 manual boxes was because the immense torque would destroy it if pushed hard. Various options exist, including a specifically designed manual box from USA (Keisler) but the cost of importing is prohibitive, at least for me. After weighing all the alternatives, I settled for the Jaguar number and hope for the best. I'm mechanically sympathetic so it should last a while, otherwise I will send the Overdrive unit to be modified with Sheffield Overdrive Services.
I did rebuild the Overdrive drive unit, luckily it was in a very good condition, with no visible wear in the planetary gears. The clutch plates were almost unworn, so it was just a question of putting all back together with new gaskets and a new solenoid, just to be safe. Wiring had to be done from scratch, using similar colour coded wiring and original bullet connectors for authenticity.
I did buy a rebuild kit for the gearbox, including all the bearings, synchromesh gears, gaskets, etc but upon inspection, it was in a remarkable excellent state, as it was rebuilt very recently. In fact, someone filled it with ATF (Automatic Transmission Fluid) for slicker gear changes and higher thermal protection. A trick quite often used by racing and drag teams. I just renewed the ATF although the one inside was quite red and clear with no debris.
My father had to grind the slave cylinder off as someone welded it to the side of the box. The six cylinder versions have the actuating slave cylinder on the bell housing unlike the V12. We did produce and weld to the box a small metal plate, 12mm thick, drilled and tapped, to accept the master cylinder on the side of the box. This will give us scope to in the future to replace it without hassle. The mounting lug in the Overdrive was also broken and that pushed me to take apart the unit in order to weld the alloy lug back in place, taking great care not to distort the casing when heating before welding it.
A special Jaguar bronze spigot was added to the crank to accept the box shaft, all the exterior fastener were replaced by stainless steel apart from the coupling engine-box bolts, which were merely cleaned and zinc plated. This a structural area, subject to loads of stress where normal stainless items are not recommended.
Flywheel bolts were bought from Jaguar, proper long ones for the clutch type of flywheel. These are longer than automatic box starter ring gear flyweel and are also hardened, requiring a special plate to safely secure the head bolts in place, still available new, bought from JagShop in London.
Clutch is a reinforced item from AP racing, specifically designed for the Jaguar V12, mated to the lightened alloy Fidanza flywheel, for faster engine acceleration, both bought for an excellent price from SNG Barratt.
I've only driven this car a couple of hundred of meters but everything seem to work fine, only the reverse gear taking extra effort to engage, but that is adjustable within the gear lever mechanism.
As soon I have this monster on the road, I'll let you have my first impressions, so keep in tune and watch this space to see if the Overdrive will disintegrate itself to bits!
I always knew one reason Jaguar didn't fit an Overdrive to its V12 manual boxes was because the immense torque would destroy it if pushed hard. Various options exist, including a specifically designed manual box from USA (Keisler) but the cost of importing is prohibitive, at least for me. After weighing all the alternatives, I settled for the Jaguar number and hope for the best. I'm mechanically sympathetic so it should last a while, otherwise I will send the Overdrive unit to be modified with Sheffield Overdrive Services.
I did rebuild the Overdrive drive unit, luckily it was in a very good condition, with no visible wear in the planetary gears. The clutch plates were almost unworn, so it was just a question of putting all back together with new gaskets and a new solenoid, just to be safe. Wiring had to be done from scratch, using similar colour coded wiring and original bullet connectors for authenticity.
I did buy a rebuild kit for the gearbox, including all the bearings, synchromesh gears, gaskets, etc but upon inspection, it was in a remarkable excellent state, as it was rebuilt very recently. In fact, someone filled it with ATF (Automatic Transmission Fluid) for slicker gear changes and higher thermal protection. A trick quite often used by racing and drag teams. I just renewed the ATF although the one inside was quite red and clear with no debris.
My father had to grind the slave cylinder off as someone welded it to the side of the box. The six cylinder versions have the actuating slave cylinder on the bell housing unlike the V12. We did produce and weld to the box a small metal plate, 12mm thick, drilled and tapped, to accept the master cylinder on the side of the box. This will give us scope to in the future to replace it without hassle. The mounting lug in the Overdrive was also broken and that pushed me to take apart the unit in order to weld the alloy lug back in place, taking great care not to distort the casing when heating before welding it.
A special Jaguar bronze spigot was added to the crank to accept the box shaft, all the exterior fastener were replaced by stainless steel apart from the coupling engine-box bolts, which were merely cleaned and zinc plated. This a structural area, subject to loads of stress where normal stainless items are not recommended.
Flywheel bolts were bought from Jaguar, proper long ones for the clutch type of flywheel. These are longer than automatic box starter ring gear flyweel and are also hardened, requiring a special plate to safely secure the head bolts in place, still available new, bought from JagShop in London.
Clutch is a reinforced item from AP racing, specifically designed for the Jaguar V12, mated to the lightened alloy Fidanza flywheel, for faster engine acceleration, both bought for an excellent price from SNG Barratt.
I've only driven this car a couple of hundred of meters but everything seem to work fine, only the reverse gear taking extra effort to engage, but that is adjustable within the gear lever mechanism.
As soon I have this monster on the road, I'll let you have my first impressions, so keep in tune and watch this space to see if the Overdrive will disintegrate itself to bits!
