Model 12 Auto in xj12
 

Hi all,

Im currently looking at buying an series 1 XJ12L but the main thing that is worrying me is the auto. it seems that you cant put a T400 on a BW twelve cylinder, so if i have issues with the auto im stuck having to rebuild or find a decent model 12 auto. how good were these transmissions behind the v12, did they handle the power? were they the same tranys that were used in the early xj6's. im tipping they are all a bit long in the tooth these days and finding parts/ someone who will rebuild it is probably about as likely as winning the lottery!

Thanks,
Regards Jay

The Model 12 was a very good transmission in terms of ruggedness and durabilty. It's a kissin' cousin to the widely used Ford "FMX" trans. I'm fairly sure many of the parts directly interchange.

Here in the 'States parts ....at least "soft parts".....wouldn't be much of a problem. There are many vendors specializing on older transmissions.

Soft parts would be seals, gaskets, bands, clutch plates, bushings, and the like.

However, "hard parts" might be harder to come by. These would be shafts, drums, gears, gear housings...things of that nature. Loosely speaking such parts are not required unless you have a very serious transmission failure or the transmission has been slipping very badly from wear/heat/neglect/abuse.

Assuming the trans in your candidate car seems to work well at the present, and assuming it has been decades since it was last overhauled (if ever), I would plan on doing a "soft parts overhaul" soon.....BEFORE any "hard parts" are damaged. You'll be good to go for years to come and can put your mind at ease.

Cheers
DD

How hard are the units to overhaul? is it something the diy'er could think about. i do practically everything else on my cars but every time an auto has gone on me ive always stuck a manual in its place, unfortunately, not something you can do so easily on an 12 cylinder. ide imagine the factory repair manual would be a great resource

thanks,
jay

DIY auto trans overhaul? I've always had mine professionally done but that's just me.

Others have jumped in I don't see why you can't. You gotta learn sometime and the Model 12 isn't especially complicated as far as I know.

Do read up beforehand, though.

Other with direct experience will chime in.

Cheers
DD

Another option would be to call John's Cars in Dallas, Texas. Have one of his T350 conversions behind a XK engine. Years ago a friend's dad put one in his Series II V12. He might have a kit for a T400 to go behind your engine.

As above, +heaps.

The BW12 is a cast iron sucker, and STRONG.

Ours spat 2nd gear at 180K kms,a very long time ago, and a simple refresh with only what was required was done.

Transmission shop only for me.

Car now has 505K kms and still sweet.

The BW12 is a tad "slushy" as compared to more modern units, but thats about it.

Clean fluid, keep cool, drive it forever.

the bw in my series three isnt the best box ive ever come across, the dam thing hardly ever kicks down unless you virtually stop or boot it. lucky they are a long stroke torquey motor and can pull away in top gear not like today's rubbish that needs 6 speeds!

anyway, i dont mind having a go at things. at the end of the day if i waste $400 in parts trying to save $1500 then its not all bad. although i would be tempted to hand it over to someone who knows what they are doing. i think its more the clean environment and correct tools at an auto shop that makes the difference.

can you swap the belhousings from an v12 to an xk model 12 box and use it, if so then its probably quite easy to find second hand boxes. for that matter can you swap the bell housings from an later 55 / 56 ect? just a thought. i have heard the earlier boxes are stronger though?

thanks,
jay