MK10 transmission leak

I’m in the process of sorting a 66 4.2 Mk10 I recently purchased which has an abundance of mechanical issues. One is a big transmission leak through the torque converter area, presumably front seal. Although the po drove the car for a video, it has way too many issues to drive safely (very poor brakes, no ps, sticking accelerator, etc, etc), but does shift in the lower range and drives in all 4 settings (D1,D2,L, R). I don’t find a label, but presume it’s a BW8 (no intermediate speed hold on the dash so I think not a DG250).
Questions: Is it a BW8?
Can I get it out without pulling the engine? The engine runs good, but is questionable for oil pressure/consumption, so I might have it out anyway. I’d like to run it awhile and see, rather than yard it out for a rebuild now.
Should I reseal or consider putting the rebuilt BW66 I have on the shelf in it instead?
Does John’s cars kit for the 700R4 fit in a Mk10?
I appreciate any insights, thank you.

Before removing the transmission I’d recommend trying K&W ‘Trans X’ stop leak. If the car has been sitting unused for awhile, this product may lubricate & expand the seals in the transmission. You really have nothing to lose by trying. The Trans X product was recommended to me recently to cure a leak in the Marles Varamatic steering box which persisted for years, Since using the fluid ten days ago, garage floor remains clean & dry.

unless its been changed out it should be a BW8…(has a big “8” cast on the case)

You absolutely cannot get the trans out without pulling the engine

if you are RHD a Johns kit will not fit, even a LHD is apparently problematic

a BW12 offers some benefits if you can get one cheap

I had a bad leak in my BW8 selector seal…it required me to take out the engine and trans, and partly dismantle it.

I did not change the front seal, as it wasnt leaking and requires a full dismantle.

Probably should have, it isnt that difficult to take them apart…just take a digipic of each step

did change the other seals

I do not know how easy it is to implant a BW66…theoretically is should, and it gets asked about, but I just dont see any with one in there

A BW8 shares the same soft parts as a Ford FMX, and BW12.

being iron case trans, they are stronger than the later ones

The terminal problem is the main drum can wear on its inside diameter, due to ring wear, and no replacement part is available

Educate me. In looking at various workshop manuals I see that the BW8 and BW12 mount to the bellhousing with four ears of the transmission casing and four large bolts and nuts holding the gearbox to the bellhousing, which is unlike the later BW65 and BW66 units. Why is not possible to remove the nuts of the four large mounting bolts and slide the transmission rearwards leaving the bell housing and torque converter in place? Factory WSM does say that the engine and transmission must be removed as a unit but from my knowledge over the decades many in the aftermarket have found ways to do things in a less complex fashion than called out in the WSM when the cars were new. Jaguar often did not take warranty costs into consideration when devising repair methods based on my 32 years in warranty administration. Comments and explanations welcome.

Its not possible to slide the trans rearward more than a couple of inches due to the immensely rigid boxed in trans tunnel.

There is one way that may work, hoist the vehicle, and attach a chain block to the engine, lift it at ~45*…attempt to drop the trans out at that angle…I tried that for the BW8 selector seal, but ended up taking out the entire engine and trans together…after removing bumper, bonnet, radiator, and front suspension

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Thanks for the excellent responses. I have the transX and will try it tomorrow.

John, I had some similar thoughts. BTW, I do have a 4-post lift and a high-lift transmission jack. I was thinking that by releasing the exhaust and rear engine hold down, removing the tack drive, loosening but not removing the front mounts, it would be possible to angle the engine back a bit and slide the transmission off. My old friend, Alan Gerard (rip) told me that he did this with a Mk2. Tony, what do you think? I hope the transx works and then I won’t need to deal with this.

Also btw, with fresh oil, the oil pressure came up 15-20 lbs and the exhaust cleared considerably. I’m hoping that the oil rings will free with time and use.

I think the issue that prevented this is the rear of the engine makes contact with the firewall, disallowing a steep enough angle, (with the IFS in there, and the vehicle on jackstands)

It is possible you may be able to get it right with a hoist
Trans weighs ~120lbs

Not a lot to lose by trying

take out the driveshaft, and maybe take off the rear extension housing of GB

I did not like the thought of trying to line up that 120lb trans, under the car, at a 45* angle

I took out my IFS and rebuilt it while I was in there…that gives a lot more space, and would almost certainly allow your proposed method

(with the proviso I believe the engine will need to be utterly removed from its mounts, lifted high and clear of them, the mounts and brackets removed, to allow the engine to get in to the right angle)

My V8-250 has a leaky BW35 and engine - so much engine oil & transmission fluid there’s no way to see where it’s all coming from and nobody seems to have a ‘dirty’ area these days where it can be washed down.

Does anyone have any experience of the additives that are supposed to stop leaks? Sounds too good to be true, and you have to be careful what you put in a BW35.

Doing a Google search turns up tales of joy and sorrow in equal quantities !!

There are some XJ around, apparently, that have done the opposite - bw8/12 in, bw65/66 out so if it works this way and the transmission is about the same size, it should work the other way. But the 65 and even the 66 are claimed to be much weaker, so I wouldn’t do it even if sitting on the shelf…
Does it fit? Put them side by side once the 8/12 is out since both are there. Since the Mk X is even heavier, I would stick with the old or find one with more gears that fits…

It so happens that my MOD 3.8S is undergoing a complete engine overhaul at the local British car shop. Heavy work such as this is way beyond my ability, or garage equipment. WSM shows a drawing of pulling the engine/gearbox/overdrive out from the top at about a 45 degree angle. From many years of experience my shop does not follow this procedure, and they drop the front suspension, remove the generator/PS pump, carbs, and radiator and lower the whole lump out the bottom. Well, I guess they support the lump on a rolling platform and using a four post lift raise the car off the power unit. They make it look so easy but I know better.

That’s what I did when I converted my Mk2 to manual O/D. Just like the e-type, it’s much easier to drop it out the bottom. It’s a little tricky to get the jack points right, as you can’t move the car after you drop the suspension, and you have to get the car up high enough to get the suspension out once it’s dropped. An overhead hoist would work better to pick the engine off it’s mounts, but I did it with my cherry picker by leaving the lift just high enough to slide the legs under the bottom crossbar of the lift. The Mk10 has a solid crossbar, but I think one could probably do the same. There is a lot more engine compartment space, and it may just be easier to get it out the top. One trick I learned form an old friend is to get the back of the car up as high as you can, reducing the angle for picking the engine out the top.

Trying the transX today. If I have to pull the engine, I’ll convert to 700-R4.

I just spoke to John at John’s Cars in Texas. He says it’s not a problem to get the transmission out with the engine in place. I tried to ask him specifics, but he didn’t elaborate other than it wasn’t a problem. However, he said that a mK10 or 420G will not take a 700-R4 without enlarging the right side of the tunnel by 3". I’m still considering my options, but I do have the sheet metal skills to modify the car, and it needs a carpet set anyway.

I’m pleased you found Trans X. Just follow the instructions on the bottle. Make certain to drain out enough old fluid from the transmission to be able to replace with a sufficient amount of Trans X. On the Mark 2 power steering I did this by using a turkey baster to suck out enough old PS fluid to make room for Trans X. Once you’ve refilled your transmission, make sure you reach operating temperature. If you could actually drive the car, that would be ideal. If not, with the motor running, shift the transmission selector through its gears several times. Then let the car sit overnight. Hopefully you will wake up the following morning with your transmission dipstick showing ‘full’, and a clean, dry, garage floor. Good luck, and please do share your results with us. It’s been twelve days since I ‘rehabilitated’ the PS in my car, and still, not a pink drop of fluid to be found anywhere beneath the car.

I agree if you have the right equipment, that overall this would probably be the quickest, easiest and safest method of doing the job

@OP… How much trans fluid is leaking per day ?

is it bad when the vehicle is moving (drips on exhaust) ?

make sure it isnt the selector seal

Follow up after TransX:
Added the latest version of TransX, designed for high mileage cars. It was leaking pretty profusely through the grated cover over the torque converter, enough to leave a 6" puddle with idling only a few minutes in gear - not so much in park. Not the selector seal, Tony. I ran it up and down my long driveway a few times and then back to the shop. It being a rainy day here in WA State, I could see a trail of iridescence down the blacktop. At this point it had only a steady drip. Up and down the driveway again, on the lift - no leak! I thought - whoops, maybe no fluid, but it was still full ( I actually overfilled it some anticipating leakage). However, at that moment, the coolant hose from the water pump ruptured and sent coolant all over my shop floor, necessitating a shutdown. I think that I have had a great result from this product, but will have to get the car functional again to be sure. Very positive at this moment.

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This forum is so useful. Thanks to all participants.
I just drove my 4,2bMk10, which has been showing 95-100 deg false reading for several years. Different gauge and sender changed nothing.
Someone on the forum said I needed a 10 Ohm resistor. Bought and placed behind the gauge. Now have a steady 72deg reading😊
Out of curiosity, what is the VIN of your car?
Mine is 1D75679
On the trunk lid it says

Some cars had a Mk10 emblem on the low right side of the lid…

I also have one of the first 420G cars which must have started off as a 4,2 Mk10 as it was built in June 66, but that is another story

hmmm…I know I can be wrong

I do know of another that spoke to him also and was told a RHD T7004 is just too difficult to be done, and only 1 has been, aparently the handbrake cable is an issue, amongst other things

Have a really good look at the front of that tunnel, just behind the gearbox flange.

Not just sheetmetal, major fab…anything can be done of course !

I have also researched fitting an AW4, 4 speed auto from a Toyota or Volvo…it can be done, but there is a lot of work

this bit…He says it’s not a problem to get the transmission out with the engine in place
double hmmmm

note, it is possible to dismantle the transmission piece by piece while still in the vehicle, and remove it that way, I have a link to that method

Peder, my car does not have a Mk10 emblem in the right lower boot lid. Vin # is 1D75725
You can see photos in the classified, as I bought it through this forum recently

Not well represented other than being a very solid car, which is most important. I’ll be very pleased with it when sorted, actually pretty excited about it now.

Tony, please don’t think I discount your experience - I’m scratching my head about the discrepancy. When you did this, did you unbolt the torque converter to pull it with the transmission? That would make a big difference in how far back you would have to slide the tranny. It looks like it’s enough to me, but???. I will look at the area you mention. Please send the link when you have a chance.

For now, it seems I may have escaped transmission R&R if the transX continues to work. I hope to get antifreeze back in it today. I’ll need to replace all the hoses - none seem to be available on the west coast, but it looks like a spare used xj6 series 3 hose gives me what I need for the top and bottom water pump outlet hoses.

Many thanks for the invaluable input here.

News to me. Transmission never leaked for me not even a little. You are in a much different climate however. Glad it seems to have stopped. I hope you enjoy the car she is a good girl!

No worries at all Ron, I have only done it a couple of times, and talked to others…always eager to learn of new ways for sure!

The issue is somewhat like certain E-types models I believe, some insist they have taken trans out, most say it cannot be done, and without pics, refuse to accept its possible.

You cannot slide the trans rearward more than 1" or so, due to the immensely solid and small boxed in trans tunnel

I think you would need 4" or 5" inches to get the torque convertor out out ?

Sounds like you dont have to, and I would only do it as a last resort

I am almost certain that you could achieve it by taking some parts from the rear, and then sliding it back…that is not hard to do, and I now strongly suspect this is what people are referring to as the “easy way”

link (he does the whole GB, with a V12 motor, interesting read)

I actually had to almost do this, following my replace selector seal, I did not correctly torque the valve body screws, so had to get back under, and pull stuff out till I found the issue, and put it all back together, on my back, under the car

I have a completely dismantled BW8 which I used to learn upon, so can fairly easily measure up how much extra clearance can be gained by removing the rearmost parts of the trans