Where to start?
I really dont rate the TDi conversion for exactly this kind of thing; its just FAR to easy to fit one, and then find.... and then find.... and then find....
Its just NOT a nice conversion, unless its really well thought out at the beginning, in which case the conclusion of that thinking logically is its a lot more effort or money than its worth!
The train of thought goes something like this; TDi from Dead Disco; dead easy drop into Series engine bay.
Next its found to be rather noisy and not very fast, so the notion of gearing it up strikes.
Meanwhile, other transmission issues start to rear thier head, as over drive units, if fitted start to complain loudly, as do main-box lay-shafts.....
As the TDi engine searches insidiousely for the 'weal link' just about everything that rotates between the flywheel and the wheels, starts to creak, clunk, grind or whine.......
The Dead Disco is looked at again, and the idea extends to pillage from that whatever bit of the series transmission is complaining loudest, and use that to 'beef up' the series tranmission to cope with the TDi'd power delivery.
Main box, is the LT77; wont fit straight into a series. Needs mounts adapting to suit, and an adaptor to fit the series X-fer box, and coming from a Disco, will need the bell-housing and gear-linkage from a Defender to line everything up in roughly the right place under the series floor-pan, which will also need a bit of tin bashing.
Ascroft LT77-Series adaptor plates are about £300 from memory, while the defender bell & linkage, again, due to the number of people with the same idea, sellers can often name thier own price for....
But, do that and you get a tougher main box, with less liklihood of a lay-shaft fail, and the benefit of a 25% over drive 5th gear.... though your already aware of the added stress that can put on the shafts, only the ones in the main-box should be better able to cope, and you dont have a fragile fairey to worry about.
OK, so to save the price of the Ascroft adaptor, and as the LT77 from the disco has already got it attached, what about its corresponding LT230 transfer box?
Great idea. Only there's a few problems with THAT as well. First, is lining up the props. Drive flange locations are a pain. The flanges are about 6" closer together from memory, and most of that is on the front prop flange.
This means that you need a longer prop top reach the front axle, but becouse the UJ is that much further from the cross member it goes through, you dont have clerance for suspension movement.
There are ways to get round this, and some of them can be helpful in other ways; such as moving the whole engine and transmission forwards on teh chassis rails; makes the weight distribution a lot more nose heavy and demands a Defender flat front, but gives a bit of added room for a longer prop to the back axle, which if a Salisbury can be useful in making the prop arc a bit wider.
But NOT a 'nice' way of doing the job, and still leaves you with a couple of other major hassles; first up being that the reduction in the LT230 is about 25% MORE than in the series X-fer, so you loose the advantage of the LT77's 5th gear...... unless you fit 3.5:i diffs...... bringing you back to square one!
HOWEVER; LT230 is a permenant four wheel drive gear-box, which rover elected upon originally with the Rangie, becouse it meant that the axles only had to handle half the power, each, hence they could get away with using the standard rover axles, rather than expensive Salisburies, or finding something even tougher than that.
SO, you could go back to a Rover Axle at the back end....... and THAT could more easily be fitted with a Rover diff to get 3.5:1 gearing.......
HOWEVER!
Front axle on a series was designed to be part time driven, and was not expected to be a particularly 'refined' road vehicle.
Consequently, Rover elected to fit cheaper Universal Jounts into the quarter shafts in teh swivils, rather than Constant Velocity joints.
UJ's as used on prop-shafts suffer a peculiar phenoninon; when flexed, the bent part of the shaft 'pulses' at a different speed to the straight portion, due to the gemonetry changes of the knuckle joint, and the greater teh angle of flex, so the greater the pulsing effect.
Remember what I said about power and speed; Power = Torque (or load) x Speed.
As the shaft changes speed through a knuckle joint, so the load on the shaft fluctuates. This means that its subjected to a constantly changing load, and hence you get cyclic fatigue and vibration.
On a prop-shaft, the phenominon is self compensating, to some degree, becouse you have two knuckle joints, and ideally, parallel flanges on the ends.
This means that as the shaft is 'pulsed' at the imput end by the flex at the knuckle, the knuckle at the other end, takes that 'pulse' and through the same geometry effect, in reverse, smooths the pulse back to a constant speed and load..... make sense?
OK, now, in the front axle, the shafts in the swivil only have ONE knuckle joint, so there is no complimentary knuckle to reverse the pulsing, and for a constant input speed, the front wheels themselves will 'pulse'.
And it can be quite a significcant amount! Worked it out not long ago, and I think that on a 30" wheel, steered through as little as 5Degrees, it could 'pulse' by as much as +/- 1/2" per revolution.
{Thats the 'sort' of lock you use on a typical country road at 45mphish road speed. At 'full' lock, I think that the amount of scrub could be as much as +/- 2" maybe more!}
Ie: as the wheel goes round, it can try and grab an extra half inch of tarmac, compared to a rear wheel, then in the next quarter turn drag for half an inch.....
Mean while, the wheel on the other end of the axle can be doing teh exact same thing, but not necesserily, and in fact inordinately unlikely to be 'in phase'.... so you have one wheel scrabbling ahead and another dragging behind, then them both swapping over, twice every wheel revolution.
This was NOT deemed a significant 'problem' on the series Landies, as it was ONLY ever envissaged it would happen when four wheel drive was engaged, which would NORMALLY be at both slow speed and on a 'loose' surface, where that amount of 'scrub' would have 'negligible' detremental effect, compared to the benefit the added traction could offer.
On a car driven on good tarmac at normal road speed? Well, your tyres are not going to last very well, as teh starting point, while the load and vibration are going to make themselves felt in what will feel like 'notchy' steering at low speeds and steering 'judder' or vibration at higher ones, all of which will do little to help shaft and joint life in the transmission itself.
What you really ought to have, and what Rover fitted to axles intended for permenant four wheel drive, is a 'Constant Velocity' Joint or 'CV'.
Works differently to a UJ, but does the same thing; basically its a cup and ball, with grooves in both, filled with ball-bearings, so that the cup and ball are 'splined' together, but rather than sliding alonmg a cylinder, teh splines wrap around a sphere, so that the input and output halves can bend.
Very elegant solution, but also an expensive one to manufacture; but the added cost of that was less than the added cost of stronger 2wd axles so there was an overall saving to the company, as well as performance benefits, becouse the jount doesn't suffer the geometry effects of a knuckle, so doesn't give this 'pulse' loading syndrome.
SO! To make your now permenant four wheel drive series nice to drive, and prevent this drive line shdder loading and snapping quarter shafts or UJ's, you realise you need CV joints.......
And you cant fit the CV joints from your Disco axle into the series one.
You CAN get a CV joint 'kit', from I think Paul Haystee or Zeuss, but you are looking at over £500 from memory.......
WELL! You think. OK, we cant use the bits out of the axles in the rear salisbury or the front swivils, but HEY why not use the WHOLE AXLE!?
Not only does it have the right diffs in, and the right joints in the shafts, ithey also have disc brakes on the end, and given the added performance of the TDi engine, those could be REALLY useful too, right?
Yeah! Oh.....Kay....... you just KNOW I'm going to reel off a whole load of 'problems' now, dont you? And I'm not going to diddapoint, but they are explained in great detail elsewhere on this board!
Essentially, the Disco axles are bracketed for coils, as mentioned, and 4" wider, as also mentioned, though swapping BOTH that's not such a great concern.
What IS a concern is that the front axle, has a completely different steering arrangement, which basically demands you copy over not just the front axle, but also the Disco's power steering box, and steering links.
That means majot chassis mods to fit the steering box, and use of a defender steering column to make it work.......
AND you have a lot of problems with the suspension, becouse if you try and keep the leaf-springs, the Disco steering rods are all in the way of the springs...... which begs the suggestion of using the Disco's Coil springs and radius arms, and welding the appropriate defender coil mounts to the series chassis......
What you NOW HAVE, after all that work, is no longer a Series III, its an 88" 'not quite a 90" Disco 'Hybrid', which DEMANDS SVA testing, as it has a radically altered chassis, non original engine, transmission, axles, steering and brakes, and I dont think you would managed to keep a single 'point' by the 'originality' rules, towards keeping its original registration, it would warrant a Q-Plate.
And for the cost, hassle and effort, TBH, you would have had two more valuable cars, leaving the series alone in the beginning, and probably done less work trying to patch up the rot that killed the donor Disco!
None of which is very possitive or helpful, to you.
BUT! Undettured, I can almost garantee, that you are thinking, EITHER:-
"OK, well, how 'doable' is that disco GEarbox and adaptor plate Idea?"
And / Or
"Well Could I use axles from a Toyota or something?"
Well lets quash the Toyota axle idea here to begin with. Botto line is your 'problem' is a 'Hot-rod' engine and a fragile transmission not designed to cope with it, lack of road speed, and a lot of noise when at road speed.
Different axles, WHEREVER they are sourced, wont do much if anything to solve that problem, unless they have the higher gearing in them, which we've already worked out isn't helpful, and you can get more easily and probably more cheaply, bitingthe bullet and getting the Salisbury converted to 3.5:1.
Which leaves the LT77 box and Ashcroft adaptor idea, which is, about as MUCH as I reckon is practicable or worth doing.
BUT, the 5th gear, has the same effect as the diffs, but only when you use it, and removing the SIII Mani-box, does reduce some of the risk of transmission failure. SO, to do what you want, it is QUITE a useful mod, but not a very cheap, quick or easy one, and would STILL only tackle about half of the problem.
Going much further, as pointed out, you are just climbing into a full on Hybrid build, where the benefits to be found, REALLY just aren't worth the effort, complexity, hassle and money.
So you are now thinking, "So what you are telling me was fitting a TDi was a bad idea"
And I'd be nodding my head in response!
As you went on "But its there now, so WHAT should I do?" adding quickly "I'm NOT going to take the damn thing OUT again!"
Well, no..... personally I wouldn't have put it in in the first place, but whats done is done, I guess!
So, I'd suggest, that the more sensible plan of action right here right now, would be to back up to the advice at the bottom of my last post.
Tackle the symptoms; deal with what you CAN, most easily deal with.
Go over the car, looking for anything loose or rattly and bolt it down. Fit new dorr hinges, window channels all that kind of stuff to stop bits rattling, than add sound proofing to make it more tolerable to live with what you have.
Some damage limitation might be done by removing the Turbo from the engine and using a 2.25 Diesel manifold, as per I think its the Glencoign (Spelling) Di conversion; to take some strain off the transmission.
Or leave it there and (Or even if you dont, perhaps!) be prepared for something going 'pop'.
And on that line of precaution, you could either start sourcing bits for an LT77 conversion with series X-fer adaptor, or you could try and source a second hand gear-box, and X-fer and recondition them, ready for a straight swap if/when something jams up or breaks, likewise with axles and propshafts.
I mean, you could go back to an SIII 'Rover' rear axle and pop 3.5:1 diffs in both; but you KNOW you are going to a wealer axle AND loading it harder, so you would be increasing the risk of breakage, but with spares ready to hand? Depends how much of an inconvenience that would be as opposed to the inconvenience and hassle of precaution against it.
End of the day, its all about compromise and finding one you can live with.... there are NO magic wands or all solving Panacea, I'm afraid.
