Mk10 "drivable" update

Just another follow-up. The BW8 continues to leak significantly and intermittently, and I’m going to condemn it. A reputable local transmission shop owner said that with the old hard seals, I’m not likely to make do without a rebuild. So, sometime in the next month, I’m going to pull the engine and transmission and replace the BW with a GM700r4/John’s Cars kit that I recently acquired. It will require modification of the right side of the tunnel, but it doesn’t look to me that it will be too bad with the drive train out. Besides the overdrive, the GM has a lower first band range which should help with performance off the line. Otherwise, I will likely be struggling with transmission issues forever.

I’ve heard a rumor of one car having been done in California, but have no specific information. If anyone knows more, please share. I will post when I get into it. There will be the scuttle and heater box repair when I have everything apart, so it will take some time. Currently, I have the nasty old carpets and underfelts stripped and will be replacing them along with the door cards and headliner.

The California car you refer to may be the Mark 10 owned by a guy named Micah, I cannot remember his last name. He has a mark X upon which he installed a manual transmission along with swapping out 14 inch wheels for 15 inch ones and I have seen him post photos on this Jag Lovers site. Good luck…

PS Sorry the Trans X did not work out for you, sounds like the old seals were too far gone. I used Trans X in the Marles Varamatic power steering system in my 1967 Mark 2. Since I ‘installed’ the fluid last August, the steering box has not leaked even one drop. Good luck…

No, not Micah, who has recently posted here. Someone actively doing the swap in the last year. I believe John at John’s Cars mentioned it, and I’m trying to reach him.

Yep, not me.

After getting sick of my DG250, I went with a T-5 and 17" wheels. That transmission was horrible. I had it rebuilt once and the converter done. Leaked, shifter poorly and was sluggish. T-5 makes her much more fun.

I think the BW8 was an upgrade from the DG250.

Good luck on the conversion. I looked at John’s years ago and didn’t like the looks of it. Then, I dealt with a shop in the UK with a different auto box and didn’t like their attitude. Next, I tried a different UK shop for a manual. I think it was a Getrag. Lousy place. Misleading and unprofessional. I sent the whole thing back to them and told them to shove it.

Transmission conversions on the Mark X is somewhat unknown territory. I think I was the first to put a T-5 in the Mark X. It was quite an experiment that turned out to be much simpler than going with a different auto box. VERY happy with the conversion. She is much more fun to drive. The only hard part was tracking down the original pedal box, nacelle and modifying the shifter to make it look as though she was originally a manual.

Unfortunately, the place I got mine no longer provides them. Shame, they did a real nice job. XKS Unlimited may sell something similar.


I communicated with Johns Cars re MKX-420G T7004 kit via email a few years ago

He stated for a RHD, forget it, too difficult

I believe this conversion has been done on at least 1 LHD, but I cannot recall any description of it on this forum, of which I have been on over 20yrs

I have measured up a T700 conversion for a MK9, it looks close

there is (at least) two big issues

Bellhousing to firewall…I think this might be manageable

The second issue, which I dont have an answer too, (but should as I measured it)

The length of the trans

The reason being, imo, it is immensly difficult to modify the trans tunnel

It consist of a cylinder of metal like a pipe, boxed in front & rear with square sections, like girders, under the trans tunnel sheetmetal in the vehicle

(the front diveshaft runs thru it)

It is essentially the central bracing structure for the entire floor pan

This is not apparent till the engine and trans is out

So anything is possible, but I would feel very intimidated do any mods to that section of the trans tunnel

I believe some E-types have a similar design

If the T7004 and adaptor are shorter or the same as BW8, you wont have that problem though

A BW12 from an XJ is a consideration

I would strongly advise to check if the leak is the selector shaft seal Ron, that little bastard pisses out trans oil

I took my trans out to fix this seal, and did some others whilst in there.
(and a lot of other work). My 420G no longer leaks a single drop of fluid upon the ground

A pleasing outcome for any older Jag owner :smiley:

BW8 is a strong trans the gears and body are very solid, almost identical as a FMX, which came out behind Ford 351 motors, having said that, a 55yr old trans, fair chance it has worn parts, some are NLA

I appreciate your cautionary note.
A few points to be made:

The transmission does Not leak from the selector shaft, but dumps under load from the bottom vented cover at the bellhousing level and can be copious when it does. I can’t live with a tranny spewing it’s guts all over the place.

So, the engine has to come out with the BW8. I will get a better look at the cross-member then, and have the fallback of a BW8 rebuild and refit. However, for the GM to work (as I’ve viewed the chassis on my lift), it’s going to require just removal of the boxed most forward section at the inside of the right footwell for the front of the bellhousing/adapter plate to fit, nothing on the left. This looks pretty straightforward, not structural, simply requiring a bit of carpet reshaping after filling in the void with sheetmetal. It’s just a flat panel. I agree, this would be more complicated, but maybe not impossible for a RHD car. I think it might depend on where the emergency brake lever is.

At the rear, the GM is longer and the tailstock is fairly narrow, but as John pointed out when I talked to him today, the driveshaft has a slip-yoke. There is no need to bolt up the driveshaft. From my preliminary look, I believe it works with the expectation of the rear mount and kickdown cable possibly being fiddly if different from the 420 car that the conversion kit came from.
I will Not weaken the cross-member.

I have two BW12s, one with a rebuild receipt, and have been warned away from it by the XJ crowd as not being worth the effort over the BW8.

Since I have to pull everything out, I’m committed at least to seeing if the GM will fit without herculean effort. It has the advantages of reliability, low 1st range, and overdrive. I ordered the installation manual today.

As to the Mk7, John told me it’s a pretty easy conversion. I didn’t ask, but I don’t think one has to pull the engine.

that is the main problem for RHD I believe.

There is Youtube of a guy trying (and failing) to add a V12 with another trans into a RHD

I agree 4 speeds would be excellent, and the BW12 is not really an upgrade, but is slightly stronger, and has more parts available

sounds like your front main seal is leaking, easy fix…but as you say…

ps; got your clip, email and pic via PM soon

If you need the front oil seal for the BW8 I believe I have one.

I have to go with Tony in this one. I would just replace the seal and see if that solves your problem. Then you can concentrate on other things and enjoy the car. Sometimes one opens up a can of worms, gets frustrated and sells the car. Do the cheap fix and enjoy. If it bothers you too much when she is on the road, then tear in and give it a shot. As I said before, I looked into this conversion and decided not to.

Not sure with your trans, but I was able to remove and replace without pulling the engine. I just needed a long socket extension to get some of the bell housing bolts off. A lot easier than pulling the engine. Damn cast iron beast weighed a ton.


I appreciate the opinions. I do have it on good authority (Tony and one other excellent mechanic who tried) that you cannot remove the BW8 with the engine in place. If that were the case, it would be different. I am assuming that you either removed a DG250 or a manual transmission? So, the engine has to come out for the “simple fix”. I wouldn’t dream of doing all that without overhauling the BW8 before it went back in. After 55 years, I’m surprised it works at all. I don’t see the conversion as that big a deal once everything is out, but I will prompt you to say “I told you so” if it winds up going poorly. One way or another, I’m not going to hurt the car by chopping anything that might weaken it. The right footwell is huge enough that nobody will notice the difference from the slight modification.

Have a good look Ron, you may see something I missed, and you will be looking anyway re yr conversion, but I could not initially see how you can move the trans back more than 2"

however, I since have done a bit of trans work on other vehicles since, and the BW8, following my “mishap” and found I can just remove the rear tail housing, so maybe I could get one down, (but you could also get stuck.)

Having to jack the engine/trans to different angles would be whats needed
I also purchased longer bolts to help me align & install the trans, which worked very well
(on another vehicle)

I dont think a DG250 is shorter, could be wrong

if oil is running heavily out the front it will almost certainly be the TC main seal, be careful, as the BW8 one might be different to others as the input shaft is .020" less OD than a BW12

certain hard parts are no longer available for BW8, so a complete overhaul may be impossible

the front drum for instance is a wear item, and can only be found as NOS or used items

( which speaks in favor of a T7004 conversion)

I have a couple of spare BW8s for spare hard parts

As I have mentioned, I am 99.9% certain an Aisin Warner A340 trans can be adapted and fit to Jag engines, I have done a bit of work sussing things out, including electronics, another fellow has one further developed, (non-electronic) and that reminds me to re-check Dellows engineering as I think they may even make an adaptor plate

The other person who had trouble with removing BW8 is also a very experienced mechanic, so it’s surely tricky. There is a procedure outlined in the service manual for pulling the transmission with the engine in place, but it’s clearly not possible unless you have a rolling overhead engine hoist and a lift that can work together. The procedure is barely short of pulling the engine because of the steep angle needed, and more complicated imo.

I’ll consider removing the tailstock. Seems like there wouldn’t be enough room to get a puller in there for the flange, though. Maybe after angling it down? If I fail, it doesn’t make the big job any harder. On the other hand, I don’t know that the GM could go back in like that.

I will have a measure of my spare BW8, and a look at a few things.

I easily pulled a BW12 out of an XJ12 and replaced it with a 5 speed Supra, and have done quite a few trans swaps, so I can usually work out the shortcuts

the yoke just tapped off,

(not needed on this job, but the diff yoke needed my strongest puller, i think someone got on the red loctite)

note, on a 420G/MKX, the driveshaft comes out the back (unlike some E-types I believe)

therefore, it is prudent to remove the entire assembly,for a full inspection of the trans swap situation

In your case Ron, as you need to make repairs to that heater sub floor area, an engine out is virtually inevitable

At that time you can go fully shipwright and tidy up all that firewall paint

Its a mongrel of a thing to get out & in, and I found it easier to drop down the IFS as well

Well, the transmission quit leaking, go figure - no sign of leak over intermittent driving for about 40 miles, now. So I was thinking about putting off the transmission conversion a bit. However… I put it on the rack to change the oil and there is coolant dripping off the front exhaust pipe, likely from the head or head gasket leaking out the exhaust manifold to downpipe joint. Seems this engine really wants to come out. I was just lamenting the absence of a machine shop in my area willing to do Jag cylinder heads on the xk engines forum.

Major work underway on the mk10.

Stripped the engine down today - turns out the head was from an e-type, Mk10 7D re-stamped over 7E.
What a disaster inside. It will take a full rebuild. Whoever rebuilt it before was a total idiot.
I believe I am going to be able to make the 700r4 transmission work. Will report back, but this is going to take a lot of time.

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