Hi, New to the Forum, think its great. Have been trying to find info on converting 1990 XJS V12 from auto to manual. Have read some if not all of the threads on the subject. A bit confused. Can anyone tell me if an early transmission from a V12 XJS, 1980, work in a 1990 car? And/or, can a five speed from a six cylinder car work in a V12? Many thanks. All the best,
Tim

 

Welcome to our little world. If you have not already done so, please do your intro in the new members area. Is it expected, and keeps the Moderators all warm and fuzzy.

Many a V12 has been converted over the years.

The early 1976 Jaguar manual unit is a 4 speed, and soooo rare I doubt you would find one.

Down here the Toyota Supra Twin Turbo units are used, and are deemed strong enough (just) to handle the V12 and the weight factor of the car.

I believe the Driven Man does a kit???.

Basically any trans can be fitted to any car/engine car combination, but the V12 is so brutal on manual transmissions it has to be a TOUGH unit.

I believe you will need to get the ECU (or in the Marelli case) both ECU's altered for man trans operation, but that is an area I know NOTHING about.

I seriously doubt any Jag 6 cylinder trans will handle the V12 grunt.

 

V12 4 speeds from early flat-head engined pre HE engine XJSs (about 300 were made) will be strong enough, and are on ebay from time to time at about 1200 - 1500 UKP. The bell housing will NOT fit a 1990 engine though, as the dowels and bolt patterns are different. Aftermarket bell housing and adaptors are available. Otherwise as the great XJS prophet Francis says, it is a kit. Realm Engineering in Pershore Worcs are maybe worth talking to, as they advertise kits, no idea about them, just seen their ads.

AJ6 Engineering will fix the ECUs so the engine does not go funny on the over-run, and they do know what they are doing!

Welcome to the club
Greg

 

The Driven Man provides a kit that seems very popular but it doesn't appear that they provide or even suggest a modified ECU?

I have the factory Getrag 290 in my AJ6 powered car. A nice box but I'm not sure if it can handle the V12? One thing is for sure, along with changes to the suspension and steering, a manual will completely transform the XJS experience
Cheers,

Allan

 

I *think* the Getrag 290 was used in the XJR/6 as well. If it'll hold up to the supercharged six it'll hold up behind a 5.3 V12.

Cheers
DD

 

Right you are Doug, the Getrag 290 was indeed used in the X300 XJR, I'd forgotten that

No problem handling the V12 as you say, though I reckon a bell housing adaptor might be needed.

Cheers,

Allan

 

Thanks everyone. I have seen Driven Man and others stuff. Very interesting.

I think the best thing to do is look for a Jaguar unit as one comes up on ebay or elsewhere. There is no time pressure. I did see one earlier but it got away.

Will update as things progress.

TM

 

After mid 1977 ( once Jaguar switched from the Borg Warner* transmission to the GM Turbo 400** transmission) the locating dowels aligned with Chevy manual transmission bell housing ( although the bolts don’t align ) because of the longer input shaft you will need to use an adapting plate. Something very easy to make yourself.
Depending on which Chevy manual transmission you use T 5 or a T56 you will need either a 3/4 inch, 7/8 inch, or 1 inch plate roughly 15” x18”
It takes me about a morning to drill the required holes and tap the plate for the ones holding the transmission. And if you have a band saw about 1/2 hour to cut away the excess. The first one I did I used a saber saw and that took more than an hour. In the end you wind up with a big C looking adapter.
If you want to just open a box and get all the stuff that will add about $4000 to your costs and you’ll still have to have someone install it for you.

Depending on what you pay for the transmission ( figure a good used T5 will cost around $500) while a T56 will be more. One thing is if the T56 doesn’t shaft smoothly be wary. Replacement parts quickly add up. And buying a brand new one at a cost of $4600 is actually a better deal.
You can budget about $2000-$2500 as a cost to do everything yourself. ( except I have a local drive shaft supply place modify my driveshaft to work. Figure around $100)
* the Borg Warner has a cast Iron case With a Aluminum Bell Housing.
** the GM Turbo 400 is one piece aluminum

 

I see you are in the UK.
Maybe look at Simply Performance in Surrey

https://simplyperformance.com/

Rob

 

This thread is 7 years old!

 

Hahah