I'm considering putting a TH350 or TH400 transmission into an XJ6 serII. I know the 12 cylinder cars came with the TH400 box which is a fairly large transmission. Can anyone tell me if the XJ12 had a larger transmission tunnel to accommodate the bigger auto?

 

The S2 V12 came with the BW12, until the VERY LAST few that got the TH400.

NO body changes that I am aware of between the 6cyl and 12cyl cars.

The transmission spring mount set up is slightly different between the 6 and 12, but the holes in the floor panel are all in the same position.

 

Had a '74 with 400 that I changed to 700R - no problems with fit.
Had another '74 that came with 350 and it had lots of room.

But, putting in a 200R or 700R would make a lot more sense and get
a OD gear.... Jag engine can use the 700R first gear ratio to get the
heavy car moving with the limited torque....

 

TH350 and TH400 will clear easily. TH700R4 may require minor clearancing on the rearward passenger side. IF clearancing is necessary....A few blows with a small sledge should do the trick to create a dimple for the part of the 700r4's pan rail that sticks out in that area. If your car is a series 2 it should have 3:31 diff gears and that's an ideal situation for a 700R4. The shorter 1st gear and overdrive with the 700R4 will allow your car to leap off the line and have a sedate cruise on the highway when locked up in overdrive. If you do go the 700R4 route install a corvette servo and Z28 governor before installation because they are impossible to install once the tranny is in the car. Those two items will allow the transmission to live under power and offer about 5500 RPM shift points. Best of all would be a 4L60E which can be setup to shift right precisely and electronically after it's installed.

 

When we did our 5 speed swap (big 5 speed), we had to massage the transmission tunnel with an assortment of mallets.

It came out looking great.

There was a little separation in the sheet metal at the top of the Trans tunnel, but we covered it with body sealer & it looks great.

No leaks.

 

Thanks for the feedback.


I'm leaning towards a TH350 at this stage. I agree the TH700 is a better option and is tempting. I'll have to see how far funds stretch when I move a few other projects on.


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Which shifter did you end up using when you swapped in the 4sp auto?