lol. Gave me a chuckle this morning when I read that. Any scrap yard or insurance salvage lot can probably hook you up with something better. With my DIY experience tuning/tinkering with my truck's 5spd transmission I'm leaning toward that brand with a US Shift controller you can easily fiddle with it until it shifts and functions like a manual, my truck does now and double tapping the brake signals to gear down, "tow" mode is now "sport" mode its quite nice having that kind of control. Given the older transmissions are mechanical/vaccum operated you'd probably need an array of gizmos and mods to even come close to the same effect.

 

i have my 700R4 set up for manual shift or just D for standard shifting!
i can hold any gear i select, up to 6000revs, altho in 1st it shifts into 2nd at 5500revs floored!
ron

 

I'll let you know in a couple of years when it gets on the road lol

 

To document what I learn as I go along, in the hope of helping the next fool:

My earlier idea that I could use the TC lockup to let me fit a higher-stall TC, but have it act like a more sedate unit when not needed, appears to be rubbish. TC stall is a mechanical property, and attempting to use the TC clutch to switch it on and off is asking for a burnt-out TC clutch, unless of course I'm spending a fortune on a TC with massive clutch... at silly money, which I won't spend. Maaaybe recent hi-tech units do clever stuff with TC lockup, but - for pre-2000s TCs at least: TCs lock up when you're crusing in top gear, and anything else is really fighting the OEM design. I believe the locking TC was introduced with the 4L80 in the facelift, so for owners with '88s, no soup for you.

Somone on t'internet mentioned that the facelift models have a TC with stall around 2600-2800 anyway, and since the V12 in factory tune makes peak torque at about 2800, a higher-stall TC is a trading money, fuel economy, TC temperature and driveability for very little return. Although, Ronbros talking about lighter TC and flywheel is obvious sense, as rotating mass is by far the best weight to lose if you want to liven up the beast.

The 6-speeds are interesting. For those who don't know, a 4-speed auto is the same thing as a 3-speed with overdrive; the 4th gear is achieved by engaging the OD when you're in 3rd. The 6-speeds go one further and engage the OD in each gear, giving you the sequence 1 - 1 OD - 2 - 2 OD - 3 - 3 OD. And this can be done with the 4L80E with not-too-complex electronics (although you'd surely also modify the valve body if you want a good result). It would be pointless unless you also change the ratios - that's because the problem isn't that the gears are too far apart from each other, it's that first gear is too tall but I'm not willing to have a shorter 4th and higher cruise RPMs; if I were OK with 3000 rpm on the motorway, I could find a 3.73 or 4.10 diff and be done with it. What I want is a greater overall spread, so you'd do the 6-speed conversion while also swapping the planetary gearset for one with a 2.97 first or more. Unfortunately, those gearsets are rare and pricey. Further, fitting that shorter gearset would increase the distance between the gears to a probably-unacceptable amount, which is a common complaint about the 4L60 box (which has a shorter first than the 4L80).

So, while it would techincally be possible for an owner to convert their 4L80e to a six-speed with a drill bit, a few springs and an aftermarket TCM (transmission controller), you'd be lacking in the gearset to take advantage of the mod and you'd be missing out on the R&D needed to get the shifts working well. You would do better to just f'n buy the TCI six-speed at around £5000 and figure out who can ship it to the UK for you. And I suspect this is a reasonable use of the money, if you want a great restomod.

Another option is the "second overdrive" which bolts on the back of the trans. Those cost US$3000 and also need a shorter driveshaft. They are usually overdrive, not underdrive, so you then also need a shorter diff, maybe a 4.10. That would give you a wider spread without sacrificing final drive in top. This adds complexity, needs to fit under the car, adds heat and saps a tiny bit of power... but hey, you don't need to muck with the box itself.

Another thing I've learned is that it's possible to adjust line pressure - such that you can switch between stock soft shifts and firmer sportier ones - if you are willing to muck about with PWM control. I don't think there's an option on the market, you'd have to homebrew.

So this is my plan:
- lighten the flywheel, just get it machined out a bit
- fit a custom shifter that has a bump-shift mode
- wire up some dumb electronics to achieve full manual; bypass the stock TCM when in manual mode
- rig up some PWM control to increase line pressure while in full manual
- NOT spend money on the transmission hardware
- drive the car for a bit
- if I really feel the lack of a shorter first gear over time, then I'll use a lot of very long socket extensions to get at the bell housing bolts in situ, and drop the box out from under the car without pulling the engine. Since the engine and box are currently apart, and since this will happen in the next five years if at all, you'd hope that they'll come apart OK.

 

Oh BTW @VancouverXJ6 , I'm in the UK, parts availability is very different. The car "scene" is predicated on small-displacement manual cars - your Civics and Golfs. It's only in the last decade that the US mfrs really started pushing cars here - now you see these plastic mustang-in-name-only things everywhere. Oh yeah, we got Chrysler 300Cs in spades too when they were a thing. But it's a challenge getting a big US gearbox, and the mustangs are generally not yet on the scrap heap. I can count the 6L80s and 6R80s on ebay on the fingers of one foot.

 

Have you considered a 700R4 or 4L60e.? First is much shorter and 4th is taller. It's the perfect trans for the broad power curve of the V12. Its also far less parasitic and I would describe the shifts lightning speed when compared to a 4L80e. Realty no need for more than 4 properly spaced gears with the flat curve of the Jag V12.

Jag should have used this trans but I suspect GM wouldn't allow that becasue it would have made the Jag far more competitive with the Corvette and Jag probably wanted something close to ZERO for warranty claims for a transmission they didn't make. The early 700R4's did have some issues but by the early 90's they were far more stout.

https://dellowconversions.com.au/pro...ine-adaptor-2/
This company makes and adapter.

 

I had considered it, vaguely but not seriously, because:
- all the reading I'm able to find is written by US-based enthusiasts, and they tend to disparage it - possibly because they're building 500hp lumps with narrow power bands, quite the opposite of the low-tune Jag
- needs that adapter plate (I'm betting the bolt pattern is different between the 5.3 and the 6.0, but that's easily fixed by a machine shop)
- I got the impression that they don't support a locking TC, and since I expect to do a lot of motorway miles that's a major downside - HOWEVER, I now think this is incorrect and they do have locking TCs

Maybe I need to think about it some more.

There are a couple on ebay UK right now for under £500. I'd expect to rebuild it, give it a stronger sprag or whatever. So with the rebuild kit and adapter I guess we're getting up to £1000, which is probably alright.

It's a bit shorter than the 4L80, so I'll need spacers for the driveshaft. I was amazed by the weight of the driveshaft anyway, so perhaps that can get a replacement that's lighter and a touch longer? We're getting a bit over my planned budget but, hey, as long as the wife gets a foreign holiday this year she won't care ;-)

I could rebuild it knowing that if I fk it up, at least I have the original to put back into the car. It's also about 30Kg lighter. For a switchable full manual, it'll have to be the 4L60e, as that has electronic control.

I did always wonder why JLR used the 4L80 when it's so massively overspecced.

Cheers for the idea @icsamerica

 

For completeness, factory ratios:

4L60:
3.06 1.63 1.00 0.70

4L80:
2.48 1.48 1.00 0.75

Sweet, that'll get me 80mph at about 1900 rpm or so - very comfortable. I won't even touch the 3.54 diff.

That's a huge gap from 1st to 2nd, but... hold 1st to 5400 rpm where the power peaks, then 2nd will kick in at 2850 where the torque peaks - I'm starting to like this idea more and more!

No wonder the guys with narrower power bands don't like it, but yeah, looks great for the Jag with the stock cam.

 

Ha, here's ronbros and warrjon talking about it, good enough for them, good enough for me!
https://www.jaguarforums.com/forum/x...e-swap-167463/
Jaguar XJS Restoration : XJS V12 4L60e Conversion