To lock or not

[AndyG]

A number of threads here have suggested, I think, to lock the centre diff as soon as you smell green grass or dirt, or it will disintegrate.

LR state in the hand book and on decals, nothing over 40 with Centre diff locked.

I am not even quite sure why you would lock in high range, although it could envisage a muddy/snow/sand scenario but not a dirt track or paddock.

So what is right for longevity:o

[manic]

A number of threads here have suggested, I think, to lock the centre diff as soon as you smell green grass or dirt, or it will disintegrate.

LR state in the hand book and on decals, nothing over 40 with Centre diff locked.

I am not even quite sure why you would lock in high range, although it could envisage a muddy/snow/sand scenario but not a dirt track or paddock.

So what is right for longevity:o

I've been locked on loose gravel roads, up to around 80/90kph. If I'm on a surface that allows some wheel spin on take off (tdi :D), I lock up.

Did not know 40kph was a recommended limit... :o

[n plus one]

A number of threads here have suggested, I think, to lock the centre diff as soon as you smell green grass or dirt, or it will disintegrate.

LR state in the hand book and on decals, nothing over 40 with Centre diff locked.

I am not even quite sure why you would lock in high range, although it could envisage a muddy/snow/sand scenario but not a dirt track or paddock.

So what is right for longevity:o

Lock early, lock often. An unlocked LT230 with spinning wheels has a life span measured in minutes (if that).

Re use in high range, it's of use on sandy tracks and greatly improves handling on loose high speed dirt.

[AndyG]

Umm , I just did the Birdsville & Strezleki unlocked. All good, I think:o
I really don't know.

[Disco Muppet]

locked centre on high speed dirt = awesome.

[AndyG]

High speed and Defender, there's an oxymoron, but then I never said Defender earlier.

[rick130]

locked centre on high speed dirt = awesome.
I disagree, I loathe unnecessary understeer, but I'm in the minority.....

[Disco Muppet]

I'm 21, so I still drive a bit stupid :p
Could always fit an ATB centre...
Consider though yesterday I nearly rolled my echo (on a very familiar road and not going THAT fast) when the rear started trying to overtake me and I ended up in a drainage culvert, so my last memory of gravel at speed is a twitchy 2wd ****box :)
Disco unlocked is superb on slippery gravel, CDL engaged made it better IMHO, although yes it does understeer a bit more.
But then I'm in a different boat with a shorter wheelbase and different engine.

[BigJon]

I disagree, I loathe unnecessary understeer, but I'm in the minority.....


We are in the minority :D.

[rar110]

Umm , I just did the Birdsville & Strezleki unlocked. All good, I think:o I really don't know.

I did this last year centre locked. It felt right. 90kmh no issues.

[rick130]

I'm 21, so I still drive a bit stupid :p
Could always fit an ATB centre...
Consider though yesterday I nearly rolled my echo when the rear started trying to overtake me and I ended up in a drainage culvert.
Disco unlocked is superb on slippery gravel, CDL engaged made it better IMHO, although yes it does understeer a bit more.
But then I'm in a different boat with a shorter wheelbase and different engine.

Muppet, an ex-racer here.... ;-)

And yes, wheel base can make a huge difference to stability.
The longer the wheelbase, the slower the transitions.

[Disco Muppet]

Almost an ex-Muppet here :D
Hence why the centre ATB is on my list :cool:
However that may be unattractive to the OP as I wouldn't want to go breaking open a nice new LT230....
A leaky old one like mine however...

[PAT303]

I disagree, I loathe unnecessary understeer, but I'm in the minority.....

I loathe the Yanks saying ''billy bob's crew have did adjusted sum air pressure's to get rid of sum of that push on the corners onto the straigh away''. Pat

[Ancient Mariner]

80" wb series one 200HP Detroit locker 2 wheel drive 130kph +on gravel Thats living:D Bugger now i am thinking free wheeling hubs on the Defender

[DBT]

What is it that makes an -unlocked- LT230 (allegedly) so fragile?

Does the same apply to an LT95?

I've always been cautions about staying locked too long (eg. leaving soft stuff and forgetting to unlock) and sustaining damage due to wind-up.

Now you saying I need to worry about both ends of the track?


:(

[Dopey]

80" wb series one 200HP Detroit locker 2 wheel drive 130kph +on gravel Thats living:D Bugger now i am thinking free wheeling hubs on the Defender

Sounds like fun, but what brakes were/are you using?

Mike.

[Ancient Mariner]

Sounds like fun, but what brakes were/are you using?

Mike.
Whats brakes ?11"x3"? Landy drums and shoes Holden dual circuit master cyl and booster over40 years ago
AM

[Toxic_Avenger]

I've been locked on loose gravel roads, up to around 80/90kph. If I'm on a surface that allows some wheel spin on take off (tdi :D), I lock up.

Did not know 40kph was a recommended limit... :o

On the Puma, the label on the dash recommends Max 40 MPH (60km/h).
I have run the CDL in my 2012 defender up to about 70km/h for short periods on loose gravel. Seems a little more stable



And yes, wheel base can make a huge difference to stability.
The longer the wheelbase, the slower the transitions.
That explains why my 90 is so twitchy on the dirt. I did a mad drift thru a corner coming up to a cattle grid the other day. Lets you know you're alive :eek:

[cripesamighty]

I have found this as good an explanation as any about why it's a good idea to lock your diffs on loose surfaces.

Why do Land Rover transmission units fail? - ask the expert - YouTube

[isuzurover]

What is it that makes an -unlocked- LT230 (allegedly) so fragile?

Does the same apply to an LT95?

I've always been cautions about staying locked too long (eg. leaving soft stuff and forgetting to unlock) and sustaining damage due to wind-up.

...

Dave Ashcroft sums it up best in his FAQ (read the bit I have bolded):

I have checked the adjustment but it won't come out of diff lock. Why?This is often reported after recent off roading, the centre diff is there to allow the props to turn at different speeds when cornering to stop drivetrain wind up, the speed difference is quite small and the centre diff gears are only designed to cope with these low speeds. If you are off road on snow or ice and you get wheelspin from one front wheel, what will happen is the rear prop will not be moving, the front will thus be going double speed, this means the small centre diff gears will be spinning like fury and after a matter of only a few seconds the plant gears will friction weld to the cross pins and the gears will fail etc, the result of this is that the diff will then behave as if it is locked as it in jammed with gear debris. The can happen if the driver forgets to lock the centre diff on a low traction surface or due to incorrect linkage adjustment, Please note this failure is not covered under warranty as we deem this driver error, the diff will never fail for any other reason other than excessive spinning, in which case the diff should have been locked by the driver.

There are plenty of people who have done this, and not just on snow and ice. Yes the LT95 is the same.

On the contrary, you really don't need to worry about wind up. Like the series LR warnings say, use of 4x4 [read CDL] on road will lead to accelerated tyre wear... ;)



On the Puma, the label on the dash recommends Max 40 MPH (60km/h). ...
The people who write manuals these days really are idiots - or rather are forced to be by the legal departments of the companies they work for.

[AndyG]

So your tootling down the Birdsville,
Gravel
Bulldust
Then a stretch of smooth hard clay and CDL is locked & your doing 90 kmph

What's the worst that is going to happen, tyre wear and wind up?

[2stroke]

There's a big difference between driving around on dirt and sitting there on ice flat to the floor and not moving. The diffs in the axle housings have small side gears as well and nobody is advocating locking front and rear diffs to drive around on dirt. I just think you need to use a bit of judgement. Windup has the potential to cause damage as well.

[roverrescue]

2stroke,
define "windup"

As best as I can determine there is no spring and nothing springy in an LT230
just a bunch of dirty great gears that are in constant mesh.
It is a stupidly simple gear box (outside of the centre diff which is a known weakness)

Once the case is locked there is no component in the t-case that will be damaged be torque before that torque is released by some other downstream component most likely tyre wear.
I would argue even 10spline axles and poxy CVs would out torque any tyre on any surface?

S

[DBT]

I would argue even 10spline axles and poxy CVs would out torque any tyre on any surface?

S

Assuming you can't get 7.50R16 (or equivalent) racing slicks ... no arguement from me Steve.

:D

[Tusker]

So your tootling down the Birdsville,
Gravel
Bulldust
Then a stretch of smooth hard clay and CDL is locked & your doing 90 kmph

What's the worst that is going to happen, tyre wear and wind up?

Nothing. Nothing bad anyway. Wind up won't happen on that sort of track if you're proceeding roughly straight ahead.

Tight turns on a high grip surface are another matter. You'll soon feel heavy steering when doing a 3 point turn with the diff in.. But it'll soon unwind as soon ax you hit some dirt. Ot just reverse for a bit if you're worried.

The centre diff isn't much bigger than a tennis ball. It'll overheat & go blue with overuse, that is high speeds on dirt unlocked.

And the car is just faster and more stable on dirt with the diff locked.

Regards
Max P

[2stroke]

2stroke,
define "windup"

As best as I can determine there is no spring and nothing springy in an LT230
just a bunch of dirty great gears that are in constant mesh.
It is a stupidly simple gear box (outside of the centre diff which is a known weakness)
Once the case is locked there is no component in the t-case that will be damaged be torque before that torque is released by some other downstream component most likely tyre wear.
I would argue even 10spline axles and poxy CVs would out torque any tyre on any surface?

S

It's unlikely you'd find your transfer case winds up driving around on dirt, though equally unlikely you'd destroy the centre diff by sitting with the throttle flat out while one front wheel is spinning, surely most people would be intelligent enough to realize they aren't moving and stop and lock it up. By windup I mean when you have the centre diff locked the splines on the front output shaft and the locking dog teeth are forced together by the different wheel speeds to such an extent that it won't disengage and if left locked and loaded for long enough could wear a groove and make engagement and disengagement difficult.
My point is that nobody worries about their front or rear diffs being destroyed by driving on dirt unlocked and rightly noone locks them because it compromises steering, same as locking the CDL.

[rick130]

The centre diff isn't much bigger than a tennis ball. It'll overheat & go blue with overuse, that is high speeds on dirt unlocked.

And the car is just faster and more stable on dirt with the diff locked.

Regards
Max P

I disagree Max, haven't had an issue with the centre diff in twelve years of abuse on high speed dirt, and just prefer the feel of an unlocked centre diff, but as stated previously, I'm in the minority !

[Tusker]

I disagree Max, haven't had an issue with the centre diff in twelve years of abuse on high speed dirt, and just prefer the feel of an unlocked centre diff, but as stated previously, I'm in the minority !

Fair enuff! These centre diffs aren't fragile, but like anything mechanical, they'll fail if you try hard enough.

Regards
Max P

[DBT]

As stated above, theres a big difference between unlocked high speed dirt and sitting still with one wheel spinning.

Somewhere In between these two extremes will be the line between normal CDL operation and destructive abuse, I imagine.

[Dervish]

The Perentie diff lock actuator is called the "cross-country" switch; according to Graeme Cooper Automotive that wording is so all of the ADF's finest know to lock the thing up whenever they're off the tarmac. So the LT95 is certainly not immune.

[DiscoMick]

I'm not convinced about high speed unsealed and locking the centre diff. I just did the Plenty, part of the Birdsville, Walkers Track and various others and did not lock the centre once and it felt fine. On the other hand, I certainly locked up in low on the Simpson.
Locking the centre at speed certainly causes more understeer.

[PAT303]

You blokes must have very different engines to what I've got,the center diff needs one side to spin up to weld itself together,what mods have you blokes done to get enough power to either the front or rear wheels to get them spinning on high speed dirt :o. Pat

[DiscoMick]

You're right, mine's a standard 300Tdi so wheel spinning is not a big issue. Ha!

[AndyG]

Well that's been an interesting discussion, :o
So my interpretation.

Stop to engage CDL, not on the fly, as that could provide a nasty shock ot the system, although it was not mentioned.

The jury is out on smooth fast gravel where there is no wheel getting excessive or lack of traction, my gut feel is unlocked.

Where traction varies significantly, ie snow, sand, bulldust and corrugations, CDL locked to prevent shock loads through the system, and keep it below 80.

This could be a pain where you get a stretch of corrugation unexpectedly on a fast section. ? (stopping to engage CDL)

[isuzurover]

...

Stop to engage CDL, not on the fly, as that could provide a nasty shock ot the system, although it was not mentioned.

...

I have never stopped to engage/disengage CDL. Just make sure you are travelling straight ahead and not accelerating hard.

When I turn onto the dirt (usually loose pea gravel in WA). I engage CDL on the fly, when I am coming up to bitumen or hard packed dirt I disengage CDL on the fly, allowing time for it to fully disengage.

[AndyG]

I always push in the clutch when engaging 4WD in a Hilux, i suppose doing same for CDL will help it along be removing any load

[vnx205]

Stop to engage CDL, not on the fly, as that could provide a nasty shock ot the system, although it was not mentioned.

As isuzurover said, no need to stop to engage or disengage CDL.

The only time there would be a nasty shock to the system would be if one or more wheels were spinning.

All you need to do to ensure that isn't happening on any surface is to momentarily push the clutch in.

[manic]

In a 90 I much prefer the added traction and understeer of a locked cd on loose gravel at speed. The 90 can be real skittish if not careful, cdl helps keep my speed in check. If I'm going too fast round a bend I'd rather have an oversteer warning instead of the rear axle overtaking me!

[dawsey]

I think cdl is under rated,,Very rarely use it myself , Have changed my opinion now!. Two weeks ago a very steep hill climb in sloppy gravel just couldn't climb it. Traction control was working overtime , 2nd or 1st gear low range but no progress, so cdl on and 1st gear low, foot off the pedals completely and it drove it self up the hill with very little wheel spin at all ..my puma can drive itself better than I can drive it...

[2stroke]

The steeper the hill the more weight you transfer from the front wheels to the rear.Thus the more you need to use the cdl. I have no qualms driving mine all day on dirt unlocked but also no problem locking it before I enter a wheelspin situation. And I lock/unlock it on the move.

[workingonit]

I've opened up 4 centre diffs. The centre diff has two weaknesses.

First. The 4 brass thrust washers. One for each of the 4 gears inside the diff. In perfect condition they keep slack out of the mechanism. The washer sits between the casing and the rotating gear, stopping steel to steel contact. Washers are sacrificial. Washers wear over time. It is easier and much cheaper to replace a washer that is out of specification than worn gears and diff casing. Add to this some reports of poor case machining from factory.

Washers wear more quickly when lubrication is restricted through build up of sediment around them, or when oil levels are low. Each washer may wear at different rates. One may be missing altogether, another with sections missing, one cigarette paper thin and one only half worn - in the one diff.

When they wear away completely or fall apart in the final stages (bits of brass in your oil change) you then have a situation of steel gear running on steel case. If you never stress your drive train ie don't go off road, then you might run almost 'indefinitely' with no problems.

Take a vehicle with some hundreds of thousands of kms, with less than routine servicing of the transfer case. The centre diff is now 'loose' or out of specification because of worn thrust washers and slightly worn pins and gear centre holes. The gears not longer hold at an unflinching 90 degrees to each other. There may be varying degrees of friction on each gear, depending on if you are now missing any thrust washers.

Add to this the second problem. The two separate pins that hold the gears in place. The pins have to cross each other but remain on the same plane. To do this the pins are machined in the middle by half their shaft diameter ie only half their strength in the centre. The pins also have to hold the gears ridgedly at 90 degrees to each other, but they don't. There is a little bit of give. That is why Ashcroft sell a one piece replacement for the two separate LRover pins.

My feeling is that under stress the brass washers do not fuse under heat and jam the diff. They simply fall apart under pressure and rapid rotation, even when new, but particularly if already very worn. All this play then adds to the movement of the cross pins which then break in their centres where they have been machined to half their diameter. Locking the diff gets around the slackness or play.

On tarmac, I think you could drive all day with the diff locked. But you would have tyre wear and lots of vehicle vibration as the axles relieved them selves by forcing the tyre to lose traction by skidding. I drove an old Toyota like that after my friend took it for a test drive but did not disengage 4x4. Yes, you might break some other part of the drive train, but it would be along time coming under these conditions. So brief moments on hard pack between lots of soft stuff won't hurt.

On good gravel roads. I think not going to hurt if locked or unlocked. Differentiation unlocked will generally be within the units design range. Depends on whether you like the understeer.

On high speed corrugations, same as above. If locked, understeer probably not so obvious. On corrugations all wheels are momentarily losing traction to relieve any wind up, and wind up is unlikely as the time interval between crests is not sufficient to allow appreciable increase in rotation of one wheel against all others.

Off road, or generally good gravel but with say lots sand drifts or patches of mud, I would drive locked.

Again, Ashcroft make the solid pin centre, but you'll still have to maintain your thrust washers. They also make the auto torque biasing diff that can take some power away from the wheel losing traction - is good in changing road conditions without the need to be constantly locking and unlocking - but that can be locked in the really difficult stuff. Locking distributes power 50:50, but is also there to protect the Rover diff itself.

[workingonit]

If my first reply was not long enough already...

On a slight tangent. Most of our vehicles rack up their mileage on good roads, high range, unlocked. The gears/dog clutch arrangements in these circumstances cop all the wear.

So your vehicle may well be able to climb that steep hill in high range. But if you could see the difference in wear between high and low, locked and unlocked components you would be quickly switching to the basically unworn configeration. Hope that makes sense.

[Disco Muppet]

They also make the auto torque biasing diff that can take some power away from the wheel losing traction - is good in changing road conditions without the need to be constantly locking and unlocking - but that can be locked in the really difficult stuff. Locking distributes power 50:50, but is also there to protect the Rover diff itself.

Also removes the thrust washers IIRC

[2stroke]

Even driving around locked has reasons why it's hard on those little bronze thrust washers on the planetary gears. When the locking dog engages it locks the front output shaft to the diff hemisphere and for any drive to go to the rear, when the front doesn't have grip the transfer gears turn the diff hemisphere until the locking dog takes up the small amount of slack it needs to operate, then the hemisphere keeps turning until the side gears push the planetary gears out into the extremity of the carrier hard into those little bronze washers. This has the tendancy to hammer those poor little guys flat and split them around the edges. As said though they are sacrificial and cheap.

[PAT303]

They are cheap to buy but not cheap to replace. Pat

[2stroke]

Hate to be paying for someone professional to do it. Took me a couple days at home, by the time the floor and tunnell come out. Though it was out for a rear main seal and clutch I took the opportunity while it was out. As well as tidying up some surface rust where the floor panels overlap.

[workingonit]

2stroke, by the time you do it four times (four strokes!?) it becomes a breeze...well, actually, not really. Still a pain.

Was thinking on your description of the locked diff and washer stress. Never considered that effect. Would guess the compression of the washer would follow on from the wear of the dog clutch. Washer takes on stress and compresses until dog clutch faces engage - compression on washer stabilises with some thinning of the washer - washer thickness and load bearing remains the same as it now matches play in dog - then the dog clutch wears a bit - so the washer comes under renewed excess pressure again until it thins enough to match play in the dogs - an so on. But must say the dogs are very tough. My previous comment ties in here now I'm thinking about this? As I indicated above, most wear on the dogs is in the high range unlocked configeration - cause that's how most of us travel. Therefore hard wheeling in high and unlocked, with worn dogs, may put the most pressure on the washers. Changing driving habits so you tackle more things in low range and locked shifts you to virtually unworn dogs and less pressure on washers. Just postulating. Are you going to throw up some other interesting things to think about? :) You can tell my wife's watching 'the block' and I've nothing better to do.

Normally I drop the whole gearbox and t/c, to do all seals, and service the centre diff - although lately I just replaced the diff with an atb.

However, I once just pulled the diff with casing off the t/c by freeing the wires and levers, leaving the rest of the t/c and gearbox in situ. I was having trouble with a detent bearing. I'd do it this way if just wanting to open the centre diff for work.

Yes, expensive to pay someone else to do it, whether replacing the washers or the whole diff. Doing it yourself is cost effective.

Bye...'survivor' has just started - means I make coffee.

[2stroke]

Must admit I was bored... I've only done 2 on an old 2 door Rangie and one on the Deefer. As for a point to all my posting, well I just think common sense is better than blanket statements and they are plenty strong enough if used in combination with that common sense.
I guess you'd be happy with the ATB then? The early LT95s had a regular clutch type LSD in them (was shown one once) but I'm told they all ended up wearing out when people didn't lock them when required.

[workingonit]

I'll be pulling my 5th centre in the next few weeks and replacing it with another atb. Basically you don't know its there. Seen this?

http://www.aulro.com/afvb/technical-chatter/207166-review-ashcroft-lt230-atb-centre-diff.html

[Loubrey]

Obviously everybody's welcome to his or her own opinion on when to lock or not lock the CDL...

Land Rover's official line at the LR Experience training centers (unfortunately not available in Australia) is that the CDL on a Defender is locked the moment there is any chance of loosing traction - that effectively includes just about all surfaces other than black top...

There is a reason the vehicle has high range diff lock and I've done more than 300,000 km in a 300Tdi 90 following that principle, so its safe to say that it certainly doesn't do the car any harm to lock up the moment you leave the black top.

60,000 on my Puma and not a trace of abnormal metal content in the transfer box or gearbox oil at the last service (both original and 48 month health check)...

Cheers,

Lou

[workingonit]

It's locked high and low.

[AndyG]

Obviously everybody's welcome to his or her own opinion on when to lock or not lock the CDL...

Land Rover's official line at the LR Experience training centers (unfortunately not available in Australia) is that the CDL on a Defender is locked the moment there is any chance of loosing traction - that effectively includes just about all surfaces other than black top...

There is a reason the vehicle has high range diff lock and I've done more than 300,000 km in a 300Tdi 90 following that principle, so its safe to say that it certainly doesn't do the car any harm to lock up the moment you leave the black top.

60,000 on my Puma and not a trace of abnormal metal content in the transfer box or gearbox oil at the last service (both original and 48 month health check)...

Cheers,

Lou

So the 40 mph / 60 km sticker on the transfer case is a piece of cover my arse by L.R

[n plus one]

So the 40 mph / 60 km sticker on the transfer case is a piece of cover my arse by L.R

In this day and age you're surprised that something's got a sticker on it which is there for arse covering purposes? :D

I'm surprised LR hasn't removed the centre diff lock from the Deefer for safety reasons - it's probably only a matter of time until cross axle diff locks will banned as unsafe as well..,

[Uber1600]

Hey all just timing in on this debate, I've just spent last week down south of wa and had my 90 in cdl for almost 4 days mainly on sand and dirt tracks and never had a drama. In regards to those saying don't drive above 40km with it engaged if you read through the owners manual it states the centre diff lock can be engaged up to 40mph or 60kph as long as the car is in a strait line with no wheel spin. And aslong as your on a loose ish surface you can dive as fast as you like with it engaged. I was driving 80kph up the beach and it performed fine. Maybe a few people need to check out and read the landrover information properly and get to understand it alittle better. By the way my 2014 90 out did all my mates patrols&landcruisers with cross axle diff locks. The centre diff lock is the real deal! Landrover must know what there doing otherwise it wouldn't be there
Cheers

[2stroke]

Surely mine isn't the only Defender with the warning sticker on the firewall in front of the gearlever saying "The differential lock must only be engaged when traction is likely to be lost... bla bla bla as soon as the difficult surface has been crossed the differential lock must be released." I don't consider a dirt road a difficult surface.

[Loubrey]

Surely mine isn't the only Defender with the warning sticker on the firewall in front of the gearlever saying "The differential lock must only be engaged when traction is likely to be lost... bla bla bla as soon as the difficult surface has been crossed the differential lock must be released." I don't consider a dirt road a difficult surface.

Because you drive a Defender!!! :D

Land Rover training doctrine considers any surface other than blacktop to have potential for losing traction...

The risk of differential speed damage running unlocked on loose gravelly dirt road remain significantly higher than running locked. Might never happen, but that's the official line.

Cheers,

Lou

[2stroke]

Still find it amusing that the centre diff is in jeopardy as soon as the vehicle leaves bitumin but the 2 in the axles, especially that poor excuse for a diff in the front, isn't. I mean one front or rear wheel has to spin up, then HALF of that speed differential has to be absorbed in the centre diff, and that's only if the vehicle is sitting stationary with an incompetent moron driver at the wheel.

[Loubrey]

2stroke,

Don't disagree at all, just the way they teach it and Land Rover Experience is usually aimed at people new to the marque who might just fall into you're descriptive category... :)

I do however find that the moment I feel the 90 being skittish on a dirt track I will notice I forgot to lock the center diff. I'd imagine 110 and 130 would be much more stable and less likely to be as noticeable.

Cheers,

Lou

[2stroke]

I've never driven a 90, in fact the shortest constant 4x4 I've driven was a 2door Rangie and it was much more stable than the 109 S2a it replaced. I reckon I could enjoy a 90 on many levels but I'd imagine the short wheelbase would have side effects. I have previously owned an 80" S1 and have been driving an LJ50 for years but neither CDL or speed are an issue on either of those.:D

[DiscoMick]

We had an interesting experience of cdl and other issues trying to get over a particularly steep and very rutted sandhill on the Simpson a couple of weeks ago.
First time I went into it in low unlocked with the tyres on about 20 and got about halfway up.
Backed down, locked the cdl, charged it again and got about two-thirds up.
Backed down, lowered the tyres to 16, charged it again and just got over.
Should mention that the rear has a Detroit auto locker in it, which makes quite a difference.
So its just a combination of steps as it gets more difficult.
On the Plenty, Birdsville and Walkers Crossing roads, I didn't feel any particular need to lock the cdl in high, as the vehicle already felt very stable. I was actually quite pleased with the way the old Disco coped with the Simpson. Our problems were not related to the basic mechanicals (except for a seized pulley on the air and a leaky heater which we bypassed) and were not that important. Fundamentally, the mechanicals proved pretty tough, including the TJM XGS coils and shocks.

[4wheeler]

Am I missing something here in this discussion? Locking the CDL just turns the Defender into every other non-constant 4x4 out there once 4 wheel drive is selected on those vehicles. All the centre diff does when unlocked is allow the defender to drive on hard surfaces in 4 wheel drive so there is no wind-up front to rear which would have an adverse effect on the gearbox or whatever the weakest component in the driveline on the day is. Why on earth, in off road situations would you not lock the centre diff? Why put added strain on the driveline and force the traction control to work more than it needs to if you have it? Centre diff lock when unlocked potentially means 1 wheel drive in some circumstances as the Defenders have open differentials and this is only overcome by the traction control system or after market accessories such as cross axle diff locks, or LDS's.

Also, why would you want to do high speed on dirt surfaces in a Defender which has the combined roof strength of a few folded tissues in a roll-over? Some of you gents/ladies are braver than me obviously.

So I select CDL for most off road situations, am careful with the power delivery if I need some momentum as I don't want to do a diff or axle. If it looks high traction, no CDL, if really loose I use CDL or if not, reduce speed so as not to work the transmission too hard. Works for me.

Just saying.