Hill descent

Maybe not all. My mother had a 33 Marathon. Maybe it made a difference in those days. 70's Kind regards, Erik-Jan.

Man there is a load of stuff in this string with some of it going in circles and disappearing up its own rear end :-)

The fact is that the diff which can be locked on a LR is the centre diff. If it is not locked in certain conditions there is a real danger that the front and rear axles will operate at different speeds as would be the case with an open axle diff in slippery conditions. If this happens on a slippery downhill condition then it is obvious that a serious situation can occur with the vehicle spinning totally out of control.

The Land Rover HDC [hill descent control] can result in an early loss of traction in my experience and it is a mercy that LR, in its wisdom, have opted to have the system switched off by default. The Mercedes ML has it switched on permanently and it can catch out the unwary on steep downhill grades on sappy grass to a dangerous degree.

Huw

It may well keep the wheels on one axle to turn together by stopping one speeding up at the other's expense.

The centre diff should never be locked at normal road speed on metalled roads. A wet road is no justification. Neither is a slippery road if it has bends. The centre diff should only be locked when there is a possibility that traction could be lost at relitively low speed.

Huw

Sorry - pure fantasy!

I have centre, rear and front diff locks fitted to my Land Cruiser. Both rear and especially the front are fairly useless and I would not waste a single penny having either fitted unless you intend hitching a plough to the back and intend to plough with one side in the furrow in greasy conditions.

Huw

Which is fantasy? Take each point in turn please.

1. The fact is that the diff which can be locked on a LR is the centre diff

1. If it is not locked in certain conditions there is a real danger that the front and rear axles will operate at different speeds

2. If this happens on a slippery downhill condition then it is obvious that a serious situation can occur with the vehicle spinning totally out of control.

I await your explanation of 'fantasy' with baited breath :-)

Huw

I'm choking here Dougal!!!!!! C...Cough....S.....splutter.

Huw

In message , Erik-Jan Geniets writes

Indeed it did, I'd forgotten about that, probably cos it never worked on mine.

It was actually a low ration button which operated on the front pulleys IIRC leaving the rears to operate normally. Hill Descent hadn't been dreamt up then, bullshit was still in its infancy,

In message , Erik-Jan Geniets writes

We had a 44, 1970 also IIRC.

In message , Huw writes

Not sure I follow your reasoning. On the one hand you consider them useless on the other hand you say they would pull a plough in conditions in which most 4x4 would be stuck solo. I found them very effective, in mud, and with 2 wheels in a rut. The rears were also very useful climbing, not so much the fronts because of the weight transfer off the front wheels and onto the rears.

Only on a tractor with deep lugs on its tyres.

I found them very effective, in

I find the rear diff lock useful only for slow rock crawling. Useless in mud because the traction limit for one wheels is so near the traction limit of the other. I've never found them to take me more than a few inches further than with an open axle diff. Of course if you actually were ploughing in greasy conditions you would know that one side of the tractor works in the furrow which is a high traction side while the other side works on the loose greasy surface. This is unusual for a 4x4 and is the reason LR have never offered an axle diff lock. It provides so little advantage in this kind of vehicle.

The front diff lock is even less value.

Oh, but one can always find the once-in-a-while moment where the axle diff-lock provides an advantage to justify its existence but I use my many vehicles offroad more than most and my main daily drive has three diff locks; one is essential while I have never found the others more than expensive toys *in this type of vehicle*.

Huw

In message , Huw writes

See Disco III spec. Perhaps LR have now realised the error of their ways.

But perhaps we'll just have to agree to differ.

Disco III has high sales expectations in America where rock crawling is much more prevelent than in Europe. In conditions of slow driving with high axle articulation with high traction, the axle diff lock is far superior to traction control or open diffs. This is not a situation that you find much in the UK and I would not expect more than a very small minority of owners to specify this option. Certainly not business users who use these things in anger, like farmers. Recreational users have different priorities and can generally find justification for wasting their disposable income.

Probably yes. I don't give tuppence for axle diff-locks and I drive one every day as well as many other vehicles, some with electronic traction control and others with LSD's. Frankly none offer a significant advantage over traction control which I find more useful than axle diff lock, which I find crude and ineffective for this type of vehicle. For my many tractors and plant equipment then diff-locks have varying degrees of usefulness. Front and rear diff-locks are most useful for tractors engaged in heavy draught work where they are commonly automatically controlled or managed.

Huw

Not all LR's have this option. Correct me when wrong.

Hardly. If a car is moving the front as well as te rear axles operate at an almost equal speed. (Almost equal is of-course different but just slightly)

Don't know.

Kind regards, Erik-Jan.

Full time four wheel drive LR's mostly have selectable centre diff lock. The ones that do not are Range Rover since late 1988 which have an automatically managed viscous centre diff and modern vehicles with electronic traction control, although newer versions of Defender and DiscoII with traction control may well have the diff lock reinstated by the owner or latterly by the factory even with HDC which regulates the speed of each wheel individually. The HDC needs to be switched on to work and frankly it is not an ideal system, which is why the centre diff lock has been reintroduced.

You have obviously not encountered the conditions I have on a fairly regular basis where traction is lost downhill. If one axle has more grip than the other but nevertheless loses traction to at least one of the high torque wheels [the front going down hill] then the two axles can and do act in the same way as two wheels on the same axle in that one axle can turn much faster than the other. This can result in a sudden loss of control with the rear end overtaking the front and the vehicle spinning out of control. This is very commonly known about and is a fundemental safety issue that no driver of such a vehicle should be ignorant of.

Well now you do and, if you think about it, the logic is impeccable and you will have no excuse if it happens! There are those that play with vehicles and there are those that depend on them, often for their life. It continues to amaze me that drivers do not endeavour to know how their vehicles work in order to get the best out of them on and off road. The safety of themselves, their passengers and bystanders depends on it.

Huw

I would like to add to this and ask you to imagine the rear axle [with the centre diff open and in extreme downhill] actually losing traction on both wheels. In this situation what do you think can happen? I'll tell you. With the centre diff open the front axle can gain speed at the expense of the rear which has lost it. The fact that the rear has no traction allows the front to accelerate with no resistance to the point that the rear pinion shaft can reverse direction in the same way that a single axle can have one wheel turn forwards and one backwards in a similar and perhaps parallel [or even simultaneous] situation. In fact in this situation it is normal for one rear wheel to turn in the wrong direction while the front wheels seem to gain speed with the vehicle speed and cease to hold back. It is the rear wheels, one of which turns at ground speed while the other reverses direction, that causes the typical pirouetting where the rear comes around. In summary, with an open diff and in extreme traction conditions then the propshafts that connect the front and rear axles can be seen to behave similarly to a single axle where one halfshaft turns faster than the other. If this happens front to back and side to side then it spells trouble which is why open centre diff vehicles ALWAYS have some kind of control fitted. For control and safety.

Huw

Understood. And logical. In my first statement I was assuming that there was still traction. What you describe may or will happen with an open center diff when one of the axles loose traction.

Thanks, Erik-Jan.

I sure will remember next time decending a snow covered road. We do not have much snow this winter though. Kind regards, Erik-Jan.