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Diff Lock, to lock or not to lock ????


Boydie
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Okay, I've had my Disco 300Tdi for just under 6 years now and travelled over 40% of Australia and well over 230,000 kilometres and I'm still learning.

My Disco has, in the front axle, a Detroit "Tru-Lock" differential, not a true LSD but a helically geared differential that assures some drive to both wheels regardless if one wheel is in the air or not. The rear axle has a Detroit "Locker" differential, again, not a locked differential but it is a LSD.

Okay to my poser, when is it safe to put the car into centre lock and just what is meant by "wind-up" I've only ever used the centre lock when I'm driving in deep sand and facing the possibility of getting bogged, but is it okay and safe to leave the centre diff locked when driving along on the beach for example, or do you see a sand dune, come to a halt, engage centre lock and then tackle the dune?

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You can engage diff lock on the beach, in fact anytime you are on a surface that the wheels can "slip" so windup does not take place and break one or all the diffs.

I am also learning something new every time I am out 4wheel driving. I only have the centre diff lock at this stage, thinking of getting the Eaton E-diff's for both my vehicles.

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Diff-lock can be engaged or disengaged at any road speed, so no need to stop.

However, with the vehicle in motion it is ESSENTIAL to be travelling on firm ground, in a straight line and without wheel slip, therefore DO NOT engage diff-lock if one or more wheels arre slipping... This will damage the transmission.... according to the disco owners handbook.

Driving on a normal surface with the differential locked the steering will feel stiff and excessive tyre wear will occur with the transmission 'wound up'.

Again, all the info is in the owners handbook.

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I engage diff lock when approaching an area of reduced traction drive through then disengage. Engaging on dry solid dirt or tarmac etc (except if a chance of wheels in the air) will result in wined up this is when one or more wheels travel fast than the others putting twisting stress on everything. Whined up can only be lost by disengaging diff lock (this will equalise stress between all wheels) or spining a wheel.

Mike

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I tend to lock it pretty much as soon as there is any risk of getting stuck or it becomes heavy going / soft ground. Lots of folks here don't and see it as a last resort, and lots of them break the centre diff as a result. The centre diff is supposedly much stronger when locked than when not.

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I thought if a wheel spins alot with the diff open you can blow it diff pretty quick and if you might lose traction diff should be locked. Although with 2 lsd I guess you shouldn't be able to get as much wheel spin if one is in the air.

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I lock the cdl as soon as i leave the black top, loose gravel often quickly turns to slippery hard clay then to slushy mud.

Diff-lock can be engaged or disengaged at any road speed, so no need to stop.

However, with the vehicle in motion it is ESSENTIAL to be travelling on firm ground, in a straight line and without wheel slip, therefore DO NOT engage diff-lock if one or more wheels arre slipping... This will damage the transmission.... according to the disco owners handbook.

Driving on a normal surface with the differential locked the steering will feel stiff and excessive tyre wear will occur with the transmission 'wound up'.

Again, all the info is in the owners handbook.

You will blow the center diff long before any tyre wear will occur (which will only happen on bitumen) and good luck trying to engage the CDL at anything more than rolling speed without knocking a few teeth off the gears.

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I lock the cdl as soon as i leave the black top, loose gravel often quickly turns to slippery hard clay then to slushy mud.

You will blow the center diff long before any tyre wear will occur (which will only happen on bitumen) and good luck trying to engage the CDL at anything more than rolling speed without knocking a few teeth off the gears.

I've only had to use diff-lock twice in the 27 years I've had one, and that was in a bit of snow recently and it engaged at 30mph with out any issues.

But perhaps you should read your owners handbook because that info is in there, or better still tell LR that their information in the book is wrong.

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I lock the cdl as soon as i leave the black top, loose gravel often quickly turns to slippery hard clay then to slushy mud.

You will blow the center diff long before any tyre wear will occur (which will only happen on bitumen) and good luck trying to engage the CDL at anything more than rolling speed without knocking a few teeth off the gears.

I think your confusing diff lock with hi low. Diff lock can go if at any speed. Hi low change should be done below 5 mph though it will go in at higher speeds but not without risk of damage.

Interestingly on a land rover off road coarse they suggest engaging diff lock when you leave tarmac I didn't argue the point but he did go distinctly quite when he found out my daily driver was a tomcat.

Mike

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I thought if a wheel spins alot with the diff open you can blow it diff pretty quick and if you might lose traction diff should be locked. Although with 2 lsd I guess you shouldn't be able to get as much wheel spin if one is in the air.

Was it Ashcroft that state 10 seconds of a single spinning wheel can blow the centre diff?

Diff = locked the moment you think you could possibly spin a wheel up.

Yes it was, but I don't believe it. Number of times I'm out with Al my friend with the hybrid, and he almost never locks his diff...only when he does find there's no more forward moment with it open. If these statements about spinning centre diffs were true, he'd be going through about 3 230's a week...

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The rear axle has a Detroit "Locker" differential, again, not a locked differential but it is a LSD.

To clear up this point. The Dteroit Locker is a full locker, not an LSD. It is normally locked. One wheel can unlock only when the force comes from the wheel and not the drive.

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Yes it was, but I don't believe it. Number of times I'm out with Al my friend with the hybrid, and he almost never locks his diff...only when he does find there's no more forward moment with it open. If these statements about spinning centre diffs were true, he'd be going through about 3 230's a week...

I'd assume it depends on the speed differential across the centre diff, when you spin one wheel up you can potentially spin the (small) planet gears in the centre diff at a hell of a rate compared with the amount they cope with during "normal" driving. Same as people blow axle diffs by spinning a wheel (usually it's the landing-whilst-spinning that kills 'em).

CDL in/out is a bit of a philosophical / driving-style question, running with everything open is nice if you're being gentle as it stops wheels being "forced" to slip and hence reduces the chance of breaking traction, but as soon as one wheel does lose traction, that's it.

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Well thank you all for your input,

I think the poser I put has been answered, when on sand, lock the centre differential -- it just goes to show how slow this old codger drives, as I would have done well over 110,000 kilometres on soft desert sand with the centre diff free :blush: and all that time it should have been locked (according to the gearbox guru Mr David Ashcroft - and hallowed be his name) from now on it's going to be locked!

Anderzander: I guess from the drivers seat it's impossible to say, I don't get to look at the wheels while I'm driving but having studies videos of Brutus bogged in sand (which has happened too many times) no, if one front wheel is free - that is it has no traction - the other front wheel still has drive, from the videos both are turning at the same speed.

Red90: Agreed but by "full locked" I was referring to the air or electric locker style of differential where both wheels are solid locked, with the Detroit the differential works normally until one wheel is free at which point the differential locks and drive is transmitted to both wheels equally.

Again, thank you all for your input and valued comments and advice ^_^ you never ever stop learning with a Landy, their complexity is in their simplicity

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Red90: Agreed but by "full locked" I was referring to the air or electric locker style of differential where both wheels are solid locked, with the Detroit the differential works normally until one wheel is free at which point the differential locks and drive is transmitted to both wheels equally.

Nope, they are both fully locked normally. A wheel can force it to unlock. One wheel can travel faster than the crownwheel. But neither can ever be slower. Power from the crowheel forces both wheels to move together at the same speed.

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I'm a bit late to the party, but I only have the centre diff unlocked to climb on the trailer and move around the driveway. With the V8 in trials and challenges there isn't the chance to risk running it open and remembering not give it a boot full. But the only guaranteed way to blow the centre diff that I have heard of is to try a tight turn with it 'open' by pulling the handbrake on. Other than that failures could just be wear? So that would be a good reason to lock it on any surface it won't wind up. It is maybe the toughest part on these vehicles :)

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Well thank you all for your input,

I think the poser I put has been answered, when on sand, lock the centre differential -- it just goes to show how slow this old codger drives, as I would have done well over 110,000 kilometres on soft desert sand with the centre diff free :blush: and all that time it should have been locked (according to the gearbox guru Mr David Ashcroft - and hallowed be his name) from now on it's going to be locked!

Anderzander: I guess from the drivers seat it's impossible to say, I don't get to look at the wheels while I'm driving but having studies videos of Brutus bogged in sand (which has happened too many times) no, if one front wheel is free - that is it has no traction - the other front wheel still has drive, from the videos both are turning at the same speed.

Red90: Agreed but by "full locked" I was referring to the air or electric locker style of differential where both wheels are solid locked, with the Detroit the differential works normally until one wheel is free at which point the differential locks and drive is transmitted to both wheels equally.

Again, thank you all for your input and valued comments and advice ^_^ you never ever stop learning with a Landy, their complexity is in their simplicity

You can feel from the drivers seat when you need diff lock or not.

In essence it's not hugely different to any other 4x4 that simply has 2wd/4wd. With diff lock engaged you have essentially the same thing you'd get selecting 4wd mode in most other 4x4's (that don't have a centre diff).

A way to think of it is like this. If you had all open diffs (stock Disco). Lift one wheel up off the ground. That would be the wheel that would spin and you'd have little or no drive to the other 3.

Engaging diff lock would mean both axles would drive, so one wheel in the air is not a problem. However lift diagonally opposite wheels (i.e. cross axle'd) and you are left spinning wheels.

As you have some form of traction aid in each axle, you won't really see the 1wd scenario. As both wheels on the axle will likely try to rotate. But you could find yourself in a situation of both wheels on the axle spinning and the others not doing anything. It'll feel like a 2wd vehicle with an LSD.

It's at these times when diff lock will make all 4 wheels spin. However when locked it'll reduce your turning circle, make the vehicle push on more so on slippery surfaces and as it makes all 4 wheels spin (in your case), it could cause you to dig in easier and 'tram line'/follow the contours of the terrain more so.

Windup is simply the fact that when making tight turns (low speed stuff), that the front and rear wheels want to travel at different speeds, i.e. the front prop wants to spin faster than the rear one. On tarmac this will result in a load bang, either as the front wheel suddenly jumps/slips and releases the energy, or when the transfer box breaks. On loose/slippery surfaces there will be enough wheel slip occurring that this won't be an issue.

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Gottcha, and again many thanks to you all for your in-depth explanations.

Oddly enough, on two occasions with the diff lock in it's normal unlocked position and while driving through a set of three very tight "S" bends going to my local hardware store I have heard a very loud bang emanating (I thought) from the rear axle. This explains it all and my speed through those bends will be reduced considerably from now on.

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Gottcha, and again many thanks to you all for your in-depth explanations.

Oddly enough, on two occasions with the diff lock in it's normal unlocked position and while driving through a set of three very tight "S" bends going to my local hardware store I have heard a very loud bang emanating (I thought) from the rear axle. This explains it all and my speed through those bends will be reduced considerably from now on.

I've got a D2 with a TrueTrac up front and a Detroit in the rear as well. As Red90 noted, the Detroit is a full locker, and when on solid ground you will hear it "pop" like that at times going around turns, especially if you are heavy on the pedal and hard in the turn.

Regarding CDL use, generally speaking if things are slippery and traction is poor, engaging the CDL is your best bet. However with the Detroit in the rear you will have situations when wheeling on firm ground (rock crawling as an example), where when turning tighttly the tires will not be able to slip sufficiently and that full lock from the Detroit in the rear is going to cause wind up. In these situations I will often try to disengage the CDL beforehand to prevent that, then work through the tight turn, and re-engage after if needed.

As a general rule though, if it is slippery ground it is best to avoid agressive wheel spinning without the CDL locked. The 2-piece cross pin in the LT230 transfer case is a fail point in those conditions. When its locked its not an issue. Ashcroft does have an upgrade for this though http://www.ashcroft-transmissions.co.uk/diy-rebuild-kits/lt230-rebuild-kits/hd-cross-pin.html

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Yes, I have an Ashcroft cross piece in my centre differential, my local 4WD gearbox specialist stocks them and was fairly insistent on fitting it as part of the transfer box overhaul carried out some three years ago - along with stress relieved planetary gears. The only weak point in the centre diff that remained were the silly brass shims which were replaced with similar spacer shims from a late model BMW "Mini" Cooper S

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