Hill descent

Huw wrote:

> 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

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

On Sun, 30 Jan 2005 00:08:39 -0000, "Huw"
<hedydd[nospam]@tiscali.co.uk> wrote:

>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.

From previous posts you'll know I agree with Huw, he keeps pointing
out this rock crawling business but doesn't point out the reason the
diff lock is essential here, it's because the axle articulation does
not cause all wheels to fully share the weight, one wheel can find
itself effectively hanging in air. Also there then tends to be a very
high torque requirement on the remaining driven wheels to lift the
vehicle over the step. Traction control via brakes has a problem here
as it is both power consuming and causes high torque variations in the
drive train, because to absorb one wheel being braked the opposite
wheel has to double in speed or something give in the drive train,
instantaneously. Unfortunately I have never had the experience of
using either traction control nor hill descent control.
AJH

On or around Sun, 30 Jan 2005 12:07:44 +0000, [email protected]
enlightened us thusly:

>On Sun, 30 Jan 2005 00:08:39 -0000, "Huw"
><hedydd[nospam]@tiscali.co.uk> wrote:
>
>>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.
>
>From previous posts you'll know I agree with Huw, he keeps pointing
>out this rock crawling business but doesn't point out the reason the
>diff lock is essential here, it's because the axle articulation does
>not cause all wheels to fully share the weight, one wheel can find
>itself effectively hanging in air.

Happens on firm mud /rock tracks as well, as I described.
--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Chuck didn’t reply, so George swung round in his saddle. He could just
see Chuck’s face, a white oval turned toward the sky.
'Look,' whispered Chuck, and George lifted his eyes to heaven.
(There is always a last time for everything.)
Overhead, without any fuss, the stars were going out"
Arthur C. Clarke, "The 9 billion names of God"

"Austin Shackles" <[email protected]> wrote in message
news[email protected]...
> On or around Sun, 30 Jan 2005 12:07:44 +0000, [email protected]
> enlightened us thusly:
>
>>On Sun, 30 Jan 2005 00:08:39 -0000, "Huw"
>><hedydd[nospam]@tiscali.co.uk> wrote:
>>
>>>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.
>>
>>From previous posts you'll know I agree with Huw, he keeps pointing
>>out this rock crawling business but doesn't point out the reason the
>>diff lock is essential here, it's because the axle articulation does
>>not cause all wheels to fully share the weight, one wheel can find
>>itself effectively hanging in air.
>
> Happens on firm mud /rock tracks as well, as I described.

I've seldom, if ever, found this to be a problem with LR suspension on any
'track'.
While I agree with most of AJH's post, the main difference between a steep
ascent where traction control works superbly and a 'rock crawl' is the speed
at which the wheels turn. They turn so slowly while rock crawling that the
traction control just isn't effective, possibly because the signals are not
sensitive enough to the difference in wheel speeds at such low speeds. I
tend to find traction control rather crude in this condition. Otherwise it
is an energy intensive and stressful business is traction control.

I also find HDC an extremely crude device which I prefer not to use if I can
help it because it is more likely to break traction in extremis than to
safeguard it. Before I take my new RR on the banks this Spring I shall need
to find out whether it has a viscous centre diff or whether I shall have to
switch the HDC [yuk!] on for best safety. Anyone know what the new RR has?
Viscous, electronic, Torsen or just open?

Huw

Huw

In message <[email protected]>, Huw
<hedydd@[nospam].invalid> writes
>
>"hugh" <hugh@[127.0.0.1]> wrote in message
>news:[email protected]...
>> In message <[email protected]>, Huw <hedydd@[nospam].invalid>
>> writes
>>> 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.
>> See Disco III spec. Perhaps LR have now realised the error of their ways.
>>
>
>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.
AIUI it's part of the terrain control system or whatever they call it.
Perhaps there's a LR expert who can tell us on which terrain type it is
switched in.

>Recreational users have different priorities and can generally find
>justification for wasting their disposable income.
>
>
Priority of both groups is the same - to keep moving.
>
>> But perhaps we'll just have to agree to differ.
>
>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
>
>
Well I had a 90 for a number of years equipped with front and rear axle
diff locks used for green laning and fun sites where you meet the more
extreme conditions. Time and again people would come up to me and say
how easy I made it look after they had struggled to make progress. Being
a modest sort of chap I had to explain that it wasn't my superior
driving skill, just the fact that I'd put the axle diff locks in.

I was also the one most called on for the really stuck recoveries. I
agree diff locks are crude in comparison to the technology involved in
Traction Control and yes if I was buying a new vehicle for every day use
then I would go for traction control rather than axle diff locks. But
really the difference between an axle diff lock and a centre diff lock
isn't that great in terms of getting traction, namely preventing all the
torque disappearing into a spinning wheel. Surely if they can be
effective on tractors then in principle they will work on any 4x4.

--
hugh
Reply to address is valid at the time of posting

hugh wrote:
> 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, bull**** was still in its infancy,

..... I must be not remembering it right then.
I thought the front had the spinning weights to
change up as the revs got high and the vac
operated bellows to change down so it had
enough engine breaking to feel OK and the rear
was just cones and springs to take up the slack.

I still don't remember a low ration button. I think
I've still got the Haynes manual somewhere. I'd better
look and see...

I blame forgetting things on all those beefburgurs
I ate in the 80s.

Moo
nigelH

"hugh" <hugh@[127.0.0.1]> wrote in message
news:[email protected]...
> In message <[email protected]>, Huw <hedydd@[nospam].invalid>
> writes
>>
>>"hugh" <hugh@[127.0.0.1]> wrote in message
>>news:[email protected]...
>>> In message <[email protected]>, Huw
>>> <hedydd@[nospam].invalid>
>>> writes
>>>> 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.
>>> See Disco III spec. Perhaps LR have now realised the error of their
>>> ways.
>>>
>>
>>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.
> AIUI it's part of the terrain control system or whatever they call it.
> Perhaps there's a LR expert who can tell us on which terrain type it is
> switched in.

The rear axle locking diff is not standard fit on the new Disco



>
>>Recreational users have different priorities and can generally find
>>justification for wasting their disposable income.
>>
>>
> Priority of both groups is the same - to keep moving.

One has cost effectiveness and usefulness as higher priority.
Virtually no farmers will **** around fitting axle diff locks to their
Defenders because they know it won't get them much more than a few inches
further and probably won't get them back from there.


>>
>>> But perhaps we'll just have to agree to differ.
>>
>>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
>>
>>
> Well I had a 90 for a number of years equipped with front and rear axle
> diff locks used for green laning and fun sites where you meet the more
> extreme conditions. Time and again people would come up to me and say how
> easy I made it look after they had struggled to make progress. Being a
> modest sort of chap I had to explain that it wasn't my superior driving
> skill, just the fact that I'd put the axle diff locks in.

And no doubt you had extreme tyres on as well. Great. Farmers and other
business users do not **** about like that and have tractors and such for,
what you call, extreme conditions which they try and avoid like the plague
so as not to poach the land more than neccessary.


>
> I was also the one most called on for the really stuck recoveries. I agree
> diff locks are crude in comparison to the technology involved in Traction
> Control and yes if I was buying a new vehicle for every day use then I
> would go for traction control rather than axle diff locks. But really the
> difference between an axle diff lock and a centre diff lock isn't that
> great in terms of getting traction, namely preventing all the torque
> disappearing into a spinning wheel. Surely if they can be effective on
> tractors then in principle they will work on any 4x4.

Yes they will but the use of a diff lock presumes that there is traction for
it to work. A heavy draught tractor pulls many tons of draught in conditions
which, as a rule, vary considerably from one side, the land side, to the
furrow side. They have deep lug, self cleaning traction tyres and their
primary purpose is to pull loads.
The LR OTOH is likely to pull on greasy surfaces which do not offer much
traction and which is likely to provide near enough equal traction to both
sides. Now you will say that the axle diff locks provide an advantage in
competition. Sure, mainly because of the twisters purposley built in the
course. But in everyday use, even serious use, they are of no use. My LR is
used off road almost every day all year and I have never felt the need for
axle locks. The LCruiser has them and I sometimes lock the back [and *very*
occassionally the front] only to find the LR whiz past where I come to a
stop. That is mostly down to the tyres of course but does show that tyres
are far and away more important than axle locks.


Huw

In message <1107162982.9bf4255d28a989eb311186d2aadccad9@teranews>, Nigel
Hewitt <[email protected]> writes
>hugh wrote:
>> 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, bull**** was still in its infancy,
>
>.... I must be not remembering it right then.
>I thought the front had the spinning weights to
>change up as the revs got high and the vac
>operated bellows to change down so it had
>enough engine breaking to feel OK and the rear
>was just cones and springs to take up the slack.
>
>I still don't remember a low ration button. I think
>I've still got the Haynes manual somewhere. I'd better
>look and see...
>
>I blame forgetting things on all those beefburgurs
>I ate in the 80s.
>
>Moo
>nigelH
>
>
I just blame it on senility. The front pulleys were controlled by engine
vac, the rears by centrifugal force according to wheel spin, moved apart
so pulley diameter was reduced as speed built up, i.e. gearing got
higher. The whole thing was then mounted on a sled with springs to keep
the belts in tension. Long time ago so I may be wrong.

The clutch was also centrifugal, in two stages. Amazing that it ever
worked.
--
hugh
Reply to address is valid at the time of posting

In message <[email protected]>, Huw
<hedydd@[nospam].invalid> writes
>
>"hugh" <hugh@[127.0.0.1]> wrote in message
>news:[email protected]...
>> In message <[email protected]>, Huw <hedydd@[nospam].invalid>
>> writes
>>>
>>>"hugh" <hugh@[127.0.0.1]> wrote in message
>>>news:[email protected]...
>>>> In message <[email protected]>, Huw
>>>> <hedydd@[nospam].invalid>
>>>> writes
>>>>> 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.
>>>> See Disco III spec. Perhaps LR have now realised the error of their
>>>> ways.
>>>>
>>>
>>>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.
>> AIUI it's part of the terrain control system or whatever they call it.
>> Perhaps there's a LR expert who can tell us on which terrain type it is
>> switched in.
>
>The rear axle locking diff is not standard fit on the new Disco
>
>
>
>>
>>>Recreational users have different priorities and can generally find
>>>justification for wasting their disposable income.
>>>
>>>
>> Priority of both groups is the same - to keep moving.
>
>One has cost effectiveness and usefulness as higher priority.
>Virtually no farmers will **** around fitting axle diff locks to their
>Defenders because they know it won't get them much more than a few inches
>further and probably won't get them back from there.
>
>
>>>
>>>> But perhaps we'll just have to agree to differ.
>>>
>>>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
>>>
>>>
>> Well I had a 90 for a number of years equipped with front and rear axle
>> diff locks used for green laning and fun sites where you meet the more
>> extreme conditions. Time and again people would come up to me and say how
>> easy I made it look after they had struggled to make progress. Being a
>> modest sort of chap I had to explain that it wasn't my superior driving
>> skill, just the fact that I'd put the axle diff locks in.
>
>And no doubt you had extreme tyres on as well. Great. Farmers and other
>business users do not **** about like that and have tractors and such for,
>what you call, extreme conditions which they try and avoid like the plague
>so as not to poach the land more than neccessary.
>
>
>>
>> I was also the one most called on for the really stuck recoveries. I agree
>> diff locks are crude in comparison to the technology involved in Traction
>> Control and yes if I was buying a new vehicle for every day use then I
>> would go for traction control rather than axle diff locks. But really the
>> difference between an axle diff lock and a centre diff lock isn't that
>> great in terms of getting traction, namely preventing all the torque
>> disappearing into a spinning wheel. Surely if they can be effective on
>> tractors then in principle they will work on any 4x4.
>
>Yes they will but the use of a diff lock presumes that there is traction for
>it to work. A heavy draught tractor pulls many tons of draught in conditions
>which, as a rule, vary considerably from one side, the land side, to the
>furrow side. They have deep lug, self cleaning traction tyres and their
>primary purpose is to pull loads.
>The LR OTOH is likely to pull on greasy surfaces which do not offer much
>traction and which is likely to provide near enough equal traction to both
>sides. Now you will say that the axle diff locks provide an advantage in
>competition. Sure, mainly because of the twisters purposley built in the
>course. But in everyday use, even serious use, they are of no use. My LR is
>used off road almost every day all year and I have never felt the need for
>axle locks. The LCruiser has them and I sometimes lock the back [and *very*
>occassionally the front] only to find the LR whiz past where I come to a
>stop. That is mostly down to the tyres of course but does show that tyres
>are far and away more important than axle locks.
>
>
>Huw
>
>
I actually had nothing more extreme than BFG MTs. But yes, I agree with
you again, tyres are the most important single factor in off road
traction, and if you are basing your assessment on the effectiveness of
diff locks on a vehicle with normal road tyres then I'm not entirely
surprised that you are less than enthusiastic about them.

But generally 4 wheel drive is better than 2 wheel drive is better than
1 wheel drive or to put it another way, 3 diffs locked is better than 1
diff locked is better than no diffs locked. Whether it is cost effective
or value for money is a matter of personal preference, like most things
in life.
--
hugh
Reply to address is valid at the time of posting