XJS 91 Facelift V12 Auto to manual gearbox conversion.

[xjscharlie]

Hello Folks,
I'm looking for some info/advice on converting my 91 Facelift V12 from 3 speed GM400 to a manual box.
Preferably from someone who has had this done and can advise on where and when and overall cost ect.
Thanx in anticipation.

Charlie.

[ChrisDixon]

Jaguar World ran an article last year, featuring these guys:
http://simplyperformance.com/v12-5-speed-conversion/
They are in Surrey and run a demonstrator. In contemplating a conversion overall gearing needs to be evaluated, you may also need to look at different final drive ratios depending on your performance/economy goals.

[pimgmx]

...featuring these guys...

I recently bought their full conversion kit for my '89 V12 after a lengthy email conversation with them. I had a ton of questions (am still quite new to the XJ-S), and living on the Continent means a quick visit to Simply Performance wasn't in the books.

I also looked at the US conversion kit using a Tremec 'box, but reviews of that kit's quality (poor fit, missing/broken/incorrect parts) quickly put me off that scenario. Another option was a kit from Down Under with a Japanese (Supra iirc?) gearbox, I took that off the list because of the prohibitive shipping and import costs...

Which left me with Simply Perfomance...
I already knew of their existence because of their performance exhaust parts (also on my shopping list ), and after reading several positive online/magazine reviews about their manual conversion kits I knew I this could be the right place. A personal recommendation from a former Jaguar engineering boffin who runs his own tuning shop was the final push in the right direction...

Simply Performance knows their stuff in and out, are very friendly (they took all the time answering my questions in great detail!) and transparent in their communication; buying from them was a pleasant and painless experience.

They offer a 'Chinese menu', where you decide which boxes you want to tick for your conversion, ranging from a 'DIY' to 'all ingredients on a single pallet' scenario.
Prices for all the key parts are on their web site, it doesn't get much more transparent than that: http://simplyperformance.com/wp-content ... celist.pdf
An illustrated 'how to' manual is also included, giving sufficient guidance for the local workshop or for an experienced DIY-er.

You can buy just the aluminium gearbox adapter ring, which will be the bare minimum needed for a conversion, and source the other conversion parts yourself, or go Full Monty and order their full kit. This even includes a manual-spec ski slope and leather gaiter for the shifter! You can also order smaller (clutch) parts on the side, but they can talk you through what you do/do not need...

Prices for fitting the conversion kit will depend on various factors:
- hourly rate of your workshop (or are you brave enough to DIY? )
- replacement/overhaul of other components in the process (quite common to tackle other jobs while 'going in deep')
- completeness of the conversion kit: i.e. other parts to be sourced/modified/fabricated?

The full kit shouldn't take more than a few days in the workshop, suggesting that - quite rare nowadays! - labour is the smaller cost component of this adventure.

Do note that Simply Performance depends on availability of donor Getrag gearboxes to 'build' the full conversion kit, so be prepared for some lead time in case you decide to order!

...you may also need to look at different final drive ratios depending on your performance/economy goals...

Just my tuppence: my post-conversion car is destined to be a long-distance GT, but should be capable to handle the occasional hillclimb/mountain pass.
I'll be applying a performance mod or two to the intake & exhaust system and will add a rear ARB plus an uprated front ARB and modified steering bushes for better cornering. The diff ratio (after consulting with Simply Performance) will stay as-is, though: a diff optimised for sprinting will compromise long-distance performance and vice versa...

[xjscharlie]

Many thanx for the prompt and informative reply. Its certainly not a job for the amateur mechanic. Rgds.

[BigCatXJS]

I run a 1989 V12 5.3 with Getrag 265 and original 2.88 diff. We used a doner 3.6 XJS and Simply Performance adaptor plate. The biggest challenge was the gear box mount as I also run the AJ6 TT extractor exhaust system that meant a tight fit in the transmission tunnel. After 3 years light use (well - apart from the hill climbs) the gear box mount has needed to be re-manufactured. Much better now and no more exhaust / tunnel clonking noises! I run 17" wheels so the gearing is slightly different. Very fast for a 28 year old car (the V12 noise - twin tail boxes also deployed - and low seating position makes you think that you are going faster than what you are - probably a good thing!) and so much fun...

[robv12]

David Marks Garages have just completed such a task, worth a call

http://www.davidmarksgarages.co.uk/