Over drives and gearboxes on V12s

Two gearbox questions related to the V12 but could not find anywhere else suitable to post.

  1. Has anyone attached an overdrive to a BW 12 - if so what model?

  2. Has anyone fitted a very late 6 or 8 speed auto to a V12 like ZF 6HP or ZF 8HP - If so what were issues to be overcome such as getting it to operate autonomously from body systems.

Just day dreaming at the moment,



I have a jag 4 speed manual with overdrive.

Its super

ok - i guess no one has considered either option.



Hi Garry, Well I’ve thought about it - mainly when cruising up the M1 at 70MPH with the V12 doing 3000RPM, whilst my 1600cc citroen diesel does the same at 2000RPM!.

Back circa 1975 whilst an apprentice at Rubery Owen, a supplier to Jaguar, after delivering a US spec Marina (awful car) back to Jaguar after a loan a Jag apprentice ran me back from Browns lane to Darlaston up the M6 in a series 2 XJ12 development car which had a two speed back axle! This was achieved by having an overdrive unit mounted to the nose of the final drive.

Around15 years ago I saw just such an arrangement for sale on E-bay but I didn’t win and I’ve never seen another.

Has anyone else seen or heard of such a development?

(1973 DDS S1)

Yes when I picked up this car I noticed straight away the high revs in fifth gear - as you indicated about 3000rpm at 105mph gps speed. On getting home I checked the gear/diff ratios and found they are the same as my Etype so the same issue exists with it as well but never noticed it - but then I was not driving a 6 speed Range Rover Sport that has 1800 rpm at the same 105kph.

Very relaxed driving.


Only barely relevant but l drove a series 1 xj12 for many years with jag 4 speed overdrive box. It was a real pleasure to drive, somewhere round 1800 rpm at our speed limit of 100kph. I even had the overdrive wired through doctored kickdown switch and regularly used it without any issues.

Yes the O/D makes nice driving on the 4speed that is why I was asking if anyone had but an O/d on the 3 speed auto.



I do Garry, but probably not the way you mean.
I am currently running a 6 litre and 4L80E in my 1989 XJRS and that is more or less a TH400 with O/D. It’s not a permanent move so kept the original diff, effortless cruising at a normal use fuel return of 10.4 litres per 100klm.

There is a guy in Sydney who has a Jag You Tube Channel and he bought a XJC with the 6 litre with the 4L80E and he too praises that engine gearbox combination. It seems as far as fuel consumption goes, Jaguar really started to sort fuel consumption issues out by then.

I want to keep my 5.3 but I might look to see if the 4l80E can be mated to it, though I believe the bell housing bolt pattern between the 6 and 5.3s is different.



Yes, the bell housing pattern is different. The 6 litre still had the original T400 mating structure in the rear face but not drilled or tapped. I did drill and tap mine as l was undecided as to whether l would fit T400 or 4L80E, the location dowels are the same for both. Of course that dual use approach can’t be used with the 5.3 so easily, however l don’t think it would be a problem given location dowels are good to go, unless yours is pre T400.

I might also add Garry, it could be done. Many years ago when getting into Jags originally l purchased my first MkVii along with a spare parts car and other parts.
This left me with a couple of 4 speed O/D boxes. I removed the O/D unit from one and made a face plate bearing/seal setup, modified mainshaft with welded uni flange. I mounted this in place of tailshaft centre bearing. I towed a caravan with this set up to Darwin when we moved there back in the 70’s without issue.
Can’t remember the revs with both O/D’s engaged but it wasn’t a lot. (XK 3.4litre)

6 or more gears is great with low torque engines or engines you have to keep in a narrow RPM band to get some performance. Neither the XK or V12 fall in that category so a 5 speed or 4 speed with OD is the sweet spot.

My Series 3 cruises 80mph at 2500rpm with the JT5. No need for less

A year ago we rented an Audi crossover with a turbo four banger, I think it had a 7 speed auto. Awful drivetrain, it was always shifting back and forth.

5 speed is perfect.

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These guys could probably guide you on a ZF8. You can get them easily and cheaply from a wrecked later model Jag diesel and keep the drivetrain all Jag.

That 4.7 first gear would certainly perk up the e type.

Thats interesting. Looking for an alternative to the BW12 in the XJC not the Etype. A ZF6 or a ZF8 would be a great auto gearbox behind a V12 as you would be in an appropriate gear all the time. The both boxes can easily handle the V12s torque as they are behind supercharged V8s in both the Jaguar and Land Rover products. A lockup torque converter would be good too. Not so cheap though even from wreckers.

I am not a person who likes to lead the field in modifications, I prefer others to blaze the trail and make the mistakes so I don’t :innocent:.

So if anyone has actually fitted a ZF 6 or 8 speed auto behind a V12 please let us know how it went.


Garry I was hoping you would want to go first.

I don’t know why these conversions are so expensive. The controller is a Quick 6 and I think about AUD2K, easy to google. The gearbox a Ford 6R80 (beefed up ZF6) which is easily obtained in the US.

Re the ZF8 I think a secondhand box from a diesel Jag in the UK wouldn’t be that much. They are a ZF8 70 version so beefy enough. Plus they are good quality being bought from ZF rather than manufactured in-house like the Dodge version. Dodge and BMW ZF8 are in reasonably high demand because there are adaptors to put them in everything from landcruisers to skylines. Not so with the Jag version which has a unique bell housing pattern. You would need a custom adapter plate but with CAD files there are many companies that could do one.

Interesting - it is a shame they had to use the Ford 6R80 rather than the ZF6HP as the 6R80 out of the Australian Ford Ranger has a very poor reputation.

So it can be done but at a huge price.


I believe those issues are unique to the Ranger (torque converter?) and the box from the Mustang has a great reputation.

Sooner or later someone will come up with an adaptor plate and savvy DIY types will be able do the 6R80 conversion for a reasonable price.

If you want to an overdrive and faster shift you could go the tried and tested GM 4L60 route for approx aud3k. Have a look at the xjs forum as there should be heaps of info.

The 4L80E was used on the 6 liter V12s in the XJS. It has a lockup torque converter and 4 speed with an overdrive 4th. It is very well matched to the V12, unlike the TH400. It used a 3.54 diff which was a good match. Unfortunately, it used a different bolt pattern than the TH400 or Borg Warner, so you’d need an adapter.

The 4L80E used a separate computer in the XJS, but I believe there are aftermarket trans computers for them. The fluid pan, internal wiring harness, and the pan gasket were unique to Jaguar and Rolls Royce as compared with s normal 4L80E. I believe the bell housing was also unique.

I have a 95 XJS 6.0 with the 4L80E. Driving it is night and day different than a 5.3 with the TH400. The TH400 never feels like it is in the right gear, while the 4L80E is well matched. The V12 has enough torque that you don’t really miss having more gears.

John’s Cars in the US also makes a conversion using the TH700 OD 4 speed tranny. I don’t have any experience with that conversion, but here is a link.

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I have the 700R4 behind my pre-HE in a 1979 Series 2 XJ12, using John’s kit as well. I had the opportunity to go with a 4 speed overdrive since the stator in the torque converter of the original TH400 was slipping. The 700R4 has a particularly low 1st gear at 3.06:1 if I recall correctly. This made for significantly better takeoff from a standstill and the overdrive ratio (I forget what it is right now) is a good match with the 3.31 final drive ratio. I haven’t driven the car in years since it came apart for a respray and hasn’t been put back together since. My plan was (still is) to substitute a 6.0 engine I bought that has also been laying around for years. I’ll have to modify the adapter plate for that.

I also installed a 700r4 behind my 5.3 v12 and absolutely love the results. Transforms the car for the better 100%.

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