420 or S-Type trans tunnel - is it the same size for a manual car as it is for an automatic?

Hi all -

I know that when you are looking to convert a MKII to the 700r4 that you should ideally start out with an automatic MKII. Its not that you can’t use a manual car, its just that the transmission tunnel on the manual car will need to be widened by 2 inches, whereas the automatic car’s transmission tunnel is wide enough to start with (this is according to John’s Cars in TX).

I am looking for a 420 or 420g, and I’ve come across several manual cars, but I want an automatic - (this is not a negotiable thing where I’ll love it once I get used to shifting - Tried that with my MGB-GT - sold it after a year and haven’t missed it) My thought was that it might be possible to switch out the manual for a 700r4, but I don’t know if the transmission tunnel is smaller on the manual 420, as it is on the manual MKII - I know the 700r4 fits fine if you start with an automatic 420.

SO - question is - does anyone know if the transmission tunnel on a 420 (or S-type since I believe they are the same) is narrower in manual form than it is for the automatic? Any particular challenges going from a manual to an automatic - usually its more challenging to do the reverse.


I’ve only had 2 ‘S’ types but have converted them both to manual, in the first one I used the manual trans cover, this did not fit comfortably inside the car so I am gong to say that the tunnel is larger in the auto. For the second car I stripped out the centre portion of the cover and just used the gear lever section mated to the auto cover.

Great - thanks. I thought it might be a different size, but it would have opened up more options if the manual tunnel could accept a 700r4.

Yes automatic cars have a larger tunnel. My 420 was an automatic and I converted it to manual.

Meh- well thanks for confirming.

The tunnel on my car is still the automatic tunnel. Just opened the top for the shift lever.

Wait, so your car used to be an auto, but now its a manual? hmm…that may change things some. My intent is to drop in a 700r4 using the quarterbreed kit from John’s Cars, but I’d need to start with an automatic car, or one that used to be an automatic, depending on what all was changed to make it a manual.

It was an automatic. Little modification was needed. Remove a blanking plate for clutch master cylinder. Put individual pedal pads on in place of the large pad that went to both pedals.
I removed the column shifter. That was pretty much it. For me it transformed thr car. When I got it, it had a 700R4 in it. I traded that setup for the manual overdrive transmission and bits.

LOL - How ironic- the car had the very thing I’d be looking to install. I take it you also removed all the shift linkage etc in the engine bay and so forth? The quick solve for that would be to use something like a lokar floor shifter - have it come up in the same spot as the manual shifter - it’ll even look like a manual. Given your experience, would you expect any challenges putting the 700r4 back in? I wonder how many of these cars are converted to manuals, and if that means there are more options than I anticipated.

I was going to install the shifter from an XJ6 before the manual trade deal came up. Let me know if you are seriously interested in my car.
It’s been completely gone through mechanically.
Rebuilt brakes, suspension, steering and engine.
Has just over 2000 miles since this work. You can get a descent $$ selling the manual stuff.

I’m not hard pressed to sell but if the right person came along…

Hello fellow Jag lovers,
The transmission tunnel is most definitely larger in the automatic mk2 ‘S’ than the manual version. I’m in the process of converting from auto to manual. I’ve downloaded a photo to help you understand what’s what, and how I have attempted the swap.
All I did was cut out part of the tunnel and use that modified with a welded on lip and raised section for the gearstick mounting.
I’m no expert, but thought the photo (if it downloaded) may help you with your quest.


Thank you @cabbagebill