I'd really like to have overdrive.
Looking around, there is a conversion kit available to upgrade to the GM T700 trans.

I'm not interested in lumping, but this trans swap seems like a good modification.

Does anyone have experience with this?

 

I have no personal experience but many jag owners have gone to the 700R4/4L60 trans and are very happy. Popular swap.

Cheers
DD

 

Good to know.
I wasn't aware the 4L60 was an option as well.

 

did that swap 16yrs ago, 700R4 with shift kit, so i can hold in any gear i want!

been 16yrs no problems, at all!!!!

you should lower you final axle ratio , for acceleration in lower gears, and use the overdrive for cruising.

CONTRARY to common idea, V12 does NOT have a lot of torque, it has a long torque curve, so pulls for a longer period of time!!

 

I'm resurrecting this post. I found it while searching for this exact info. Thanks Ronbros and Doug for the info.

Does anybody on here now have any other thoughts about it - especially those that have done it?

The first gear in the T700 is supposedly pretty low, so I was under the impression I wouldn't really want to lower my rear end ratio.

I have also found something called gearvenders www.gearvendors.com that basically put another gear between them. But does anybody know how this works in a practical sense? Is it something I have to kick in manually? Say I'm in first gear, then want to go to 1.5 before 2nd gear - how does that work, do I push a button, or do you set up where it shifts and it does it automatically?

It would be great if it worked automatically. But my other thought if it was a manual button type thing, would be to lower the rear end ratio to get more pull in 1,2,3 and then only use it like an overdrive after 3rd gear.

 

i run a 700R4 in my XJS. i demolished the FWD clutch pack within the first week of driving it. i turned that entire transmission into cinnamon swirl.

 

But you still run the 700R4? After being re-built? How is it now?

It seems the 700R4 wasn't quite the tranny the TH400 is strength wise from the factory, but I was planning on putting a strengthened/rebuilt 700R4 behind the V-12. Just want to make sure that is still strong enough and how it feels to drive.

 

well the built 700R4 no longer has 3rd or 4th gear....... so thats sort of how it worked out.

 

I'm not an authority but I've spoken with some people who seem to be. In a nutshell a standard 700 should be fine behind a V12 *unless* you plan on running the engine up to the 6500 rpm level that it is capable of. In that case, the 700 will need some warming over to survive. And a suitable torque converter as well.

I might add that even the 400 needs the right converter for 6000-6500 rpm use. The typical garden variety $129.95 rebuilt t/converter won't tolerate high rpm use.

My only reservation in using a 700 behind a 5.3 V12 is the 1-2 ratio difference. It's like falling off a cliff. That's where your Gear Vendors over/under drive might play in, of course

Cheers
DD

 

some guys use a 4L80E-4L85E, very strong and lot of information coverage.

if i had a Jag V12 bigger displacment, that would be my choice, some of the 6L came with it from the factory!

of course if money no object , GM now has a 6L90E trans available, 6 speeds forward, strong as a bull, can handle 650hp.

in the mean time, my 700 is great!

 

cop, try Johns cars Dallas TX, a Jag specialist!