Hill decent and slippery stuff

[NavyDiver]

On a very slippery wet mud track, I was going down a steep slope the D3 TD6SE was getting a little out of shape. I engages hill decent. It was ok but when I tried to brake it seems to stop me breaking fully? I could feel the brake pedal engaged by hill decent increasing and decreasing. Very interesting but with the 4 wheel slipping and speed getting higher. Found the inability to brake more a little troubling. Disengaging and steering on to the side of the track enable me to regain control.
Getting back up was a perfect reason to get a winch on front. 6 attempts had me considering going down even a steeper bit of track to see if there was another way out. Lots of branches, bark and bracken added to the track on one side enabled a climb out.
Good fun but mud or slippery stuff sure adds a whole new dimension to travelling off road. If it had been dry a 2wd would have driven it with ease!

I assume the all terrain tires are my main problem on the slippery bits. It was fun as I got out without too much drama. I was driving a hired nissan patrol north of Broome in WA a few weeks ago. It was sideways on a clay road after rain storm for about 20km. I had driven up the track at 100kph 6 hours before- LOL. I am not sure what a steep mountain track would have done to it but I wonder if some settings make it better or taking us ( drivers) out of control puts us at a disatvanatge some times?;)
How does your go on clay or very slippery steep bits when traction is non existant?

[CaverD3]

Mud and ruts setting makes a huge difference. But I have a rear e-diff as well.
Tyres are more crucial on muudy surfaces though.

[gps-au]

Found the inability to brake more a little troubling. Disengaging and steering on to the side of the track enable me to regain control.

Did you use the HDC speed control at all ?

(I have found many D3 drivers don't know about it).

[RichardK]

In conjunction with HDC you can use command shift to lock it up in 1 or 2 low depending how slow you want to go, I find using command shift this way I mostly don't need HDC

[Piddler]

Slippery down hill bits you need to accelerate to clear the tyres and pull it back into shape.

Cheers

[disco2hse]

It was ok but when I tried to brake it seems to stop me breaking fully? I could feel the brake pedal engaged by hill decent increasing and decreasing. Very interesting but with the 4 wheel slipping and speed getting higher. Found the inability to brake more a little troubling. Disengaging and steering on to the side of the track enable me to regain control.

Do not use the brakes when you are using HDC! It says this in the manual too.

You must trust your machine to know what it is doing.

Alan

[camel_landy]

As the other guys have mentioned, there are a number of techniques you can use but the main ones are:


Don't use your brakes.
Get to know & trust the cars ability.
Modulate the HDC speed.
Manually select gear.

Remember that with all of this, if you do start to slide, you are going to have to use the accelerator to regain control (not your brake)!

It's also worth noting that no matter how good the car is, it can't break the rules of physics and magically find traction when none is there to be had!!!

M

[brad72]

So does the hill decent work in reverse as well. I had gone up a really steep slippery section in my D4 on the weekend in rock crawl and had to reverse out of it. The car seemed to accelerate and the abs was working like mad. Bit daunting when you want to go slow. I didn't think about using the cruise control to control the speed however as I was caught a little off guard

Thanks

[WhiteD3]

On a very slippery wet mud track, I was going down a steep slope the D3 TD6SE was getting a little out of shape. I engages hill decent.

I would have thought you'd have HDC selected before you started down? As other have said, select L1 or L2, HDC and stay off the brakes. Use the cruise +/- to change the speed.

What tyres do you have?

[gghaggis]

AT tyres will give you little to no grip on clay - most MT's will struggle too. A bit of speed might help clear the tread, but usually they'll just turn to slicks in a couple of seconds or so.

Cheers,

Gordon

[DiscoWeb]

All my experiences with HDC, and knowing about the use of cruise control to lower or increase speed have been very good.

Nursed my D3 of Mt Pinnibar, which is very steep in places (thank god not wet and slippery) due to a transmission fault using HDC and it is an amazing piece of kit, can put it in neutral if you want (not recommended!!) but tried it non the the less.

Not sure about using it in reverse but as I recall reverse is very lowly geared so in rock crawl you would have lots of engine braking control ? I am sure someone can provide gear ratios.

As has been pointed out, you only control vehicle speed when the tryes have some traction. So no matter what you or the vehicle does, if you are slipping down a track with minimal or no traction only an anchor will assist. I for one do not have an emergency anchor fitted !!

As long as it stayed upright and out of the trees you can look at it as a positive learning experience.

Regards,

George

[Xtreme]

AT tyres will give you little to no grip on clay - most MT's will struggle too. A bit of speed might help clear the tread, but usually they'll just turn to slicks in a couple of seconds or so.

Cheers,

Gordon

Fully agree with above and I would be interested to hear what your experience/thoughts are regarding the use of tyre chains in extreme clay conditions?

[disco2hse]

So does the hill decent work in reverse as well.

Absolutely it does. Again, don't go near the brakes! Nail your foot to the floor if you have to.

Alan

[Jamo]

AT tyres will give you little to no grip on clay - most MT's will struggle too. A bit of speed might help clear the tread, but usually they'll just turn to slicks in a couple of seconds or so.


As I found out once with STT's on the D3. Once they were full of mud, all the car would do is slowly pirouette.


In conjunction with HDC you can use command shift to lock it up in 1 or 2 low depending how slow you want to go, I find using command shift this way I mostly don't need HDC

The Cayenne has no HDC. When I went down a steep, loose shale and rocky slope, I locked the diffs and went into low range manual 1st. Much more control than I ever felt with HDC on the D3.

It was also when I found out about the benefits of tiptronic gear levers on the steering wheel. I could change between 1st and 2nd without taking my hands off the wheel.

I think that when it comes to slippery mud, particulartly on steep slopes, one needs to ask oneself 'do I need to go this way?'. Losing control can be very costly.

[disco2hse]

The Cayenne has no HDC. When I went down a steep, loose shale and rocky slope, I locked the diffs and went into low range manual 1st. Much more control than I ever felt with HDC on the D3.

Interesting. Of course no machine is perfect and therefore no machine will perform optimally in all conditions.

Personally I hate it when I first lurch down a slope (front or rearwards) until the computer works out what it wants to do, but once it has done that I have every confidence that it will perform as required. Then if traction is lost because of soft or slippery ground then a tweak on the accelerator usually sets it off in the right direction.

In the old Stage 1, going forwards, 1st low and no diff lock. No brakes ever and use the accelerator to maintain forwards momentum. It feels that I have more control and probably I do, but with HDC the control is handed over to Silicon Sue.

[Jamo]

But the Stage 1 is a manual box, yes?

Oh, and I didn't mention 'confidence', I only mentioned 'control';) but I suppose in some circumstances lack of one leads to lack of the other.

(My car also has an automatic terrain diffculty alert system. Whenever I have failed to heed her warnings, I have invariably run into trouble!:p)

[NavyDiver]

Did you use the HDC speed control at all ?

(I have found many D3 drivers don't know about it).+

I was using the speed control. It was working untill as pointed out in another thread. Physics took over. 2 tonnes with mud choked tires and a good incline had the car going or starting to go sideways. HDC works and the + & - works well. I read the manual from cover to cover then tried the speed control on a dry slope previosly.
Thanks for the suggestion ( I added note to user guide "nail foot to floor to remove temptation it touch brake while HDC engaged" as I over looked the bit about keeping ones foot off the brake )

[NavyDiver]

I would have thought you'd have HDC selected before you started down? As other have said, select L1 or L2, HDC and stay off the brakes. Use the cruise +/- to change the speed.

What tyres do you have?
Sorry important bit on information. they are Grabber AT 2.

review at General Grabber AT2 Tires - All Terrain Tire Reviews (http://www.offroaders.com/tech/AT-MT-Tires/General-Grabber-AT-2.htm)

the review found they work in mud untill it became deep. The track was slippery as but the mud was less than a few millimeters or a few centimeters deep after I had cut the track a little after the several attempts. Physics took over but the climb out was fun.

[disco2hse]

But the Stage 1 is a manual box, yes?

Oh, and I didn't mention 'confidence', I only mentioned 'control';) but I suppose in some circumstances lack of one leads to lack of the other.

Sorry I didn't express myself clearly enough. What I intended was that when driving the Stage 1, which is manual of course, down an incline requires a specific technique. Since it is manual I am required to pilot it and have control over all the machine's functions to ensure a safe descent. When doing the same with a HDC equipped vehicle there is a technique but it is different to that required when driving the manual Stage 1. In that instance one must pass control over to the computer brains (there are multiple) that control the vehicle's functions.

Tweaking the speed controls adjusts the parameters for the brains but using the brake pedal, or the accelerator pedal for that matter, disengages HDC and is more likely to cause problems than resolve them.

Different techniques but with the same result, hopefully. A safe and controlled descent.

Hope that's clearer.

Alan

[Jamo]

I agree. Different techniques for the conditions and the vehicle. And a bare bones D/4 on the same terrain will perfom slightly differently to one that's been loaded up. My D3 weighed around 3tn+.

The HDC must contain the momentum of the vehicle and momentum is a function of the mass. As I added bits I drifted away from using the HDC and towards driving the car myself as I found I was having more work to do with the HDC than when i controlled the descents myself.

The Cayenne is considerably lighter and, having done 165,000km in my D3, I would at this stage say that the aisin warner auto is better than the ZF. But, then again it's almost like comparing apples and oranges. One was 2005 car weighing 3tn and the other is a 2010 car weighing 2.4tn; and that makes a big difference.

Horses for courses.

[gghaggis]

Fully agree with above and I would be interested to hear what your experience/thoughts are regarding the use of tyre chains in extreme clay conditions?

I've only observed chains being used in clay/mud twice, both times by rather, er, boisterous lads. They certainly worked, but the condition they left the track in had a lot to be desired. Perhaps a more contained driver would have done less damage.

Cheers,

Gordon

[disco2hse]

I've only observed chains being used in clay/mud twice, both times by rather, er, boisterous lads. They certainly worked, but the condition they left the track in had a lot to be desired. Perhaps a more contained driver would have done less damage.

Cheers,

Gordon

Chains are used by the farming community here quite a bit. It is true that they can be used without ripping the ground apart but in general they cause a hell of a lot more damage than rubber. I have chains but I would not use them on a public track, and many clubs will not allow drivers to use chains on club runs although I have seen it done.

The correct chains (there are different types of course) on a vehicle makes a huge difference in traction, mud or clay.

[Xtreme]

I've only observed chains being used in clay/mud twice, both times by rather, er, boisterous lads. They certainly worked, but the condition they left the track in had a lot to be desired. Perhaps a more contained driver would have done less damage.

Cheers,

Gordon

Thanks for your comments Gordon.

My observation of chains being used in a situation that involved a mixture of mud and half buried tree roots was to see a number of vehicles fitted with MT tyres (no chains), spinning wheels, sliding and bouncing around before in most cases, eventually having to be snatched or winched over the obstacle. Then along came a guy with AT tyres fitted with chains and he just idled through with complete control and no more than about half a revolution of wheel spin. It was a most impressive demonstration of how effective, and when used sensibily, less damaging to vehicle and environment the chain equipped vehicle was.

I agree though, that if not used with restraint, they would do extreme damage to tracks.

It is interesting that there are many threads on very agressive, oversize MT tyres but very few, if any, on the use of chains in mud.

[gghaggis]

It is interesting that there are many threads on very agressive, oversize MT tyres but very few, if any, on the use of chains in mud.

Well, in many public areas, chains are illegal. MT's are not.

Cheers,

Gordon

[Cairns Rob]

As Extreme has said chains used sensibly in mud give amazing grip and do far less damage than spinning agressive muddies. They are absolutely awesome on slippery hard packed clay hills such as our CREB track up here. Cheers Rob

[austastar]

Hi,
in about 1964, the track into Blanket Bay (Cape Otway, Vic) was clay, and rutted with longitudinal grooves.
In an FX Holden, I was stuck with the front wheels in one groove and the rear wheels in the adjacent groove and going nowhere.
Ladder snow chains got me going again, even with a hill start.
Yes, driven conservatively you can get traction with little track disturbance.

https://www.aulro.com/afvb/

cheers

[rmp]

In my view HDC is a waste of time for any trained driver (and yes I'd love an explanation as to why it isn't). All it does is apply the brakes for you, and you can do that yourself. ABS works in low range on the D3, so I'm not seeing any advantage whatosever. HDC is of course only applying the brakes for you and does so to a set speed, it can't see the likes of a washout or spoon drain coming and slow things down more or less depending on the terrain and the manual control isn't as quick to react as foot pressure.

One technique that will help is driving through the brakes, ie holding the brakes on with your left foot and applying accelerator to force the wheel to turn slowly. That'll keep the wheels rotating whereas just applying brakes or using HDC is constantly trying to slow the wheel, not force it to rotate slowly. That makes quite a difference.

Also, HDC can be a little rough and jerky and it is not difficult to be smoother by braking yourself.

If the rear locker could be manually locked that would be nice as then you wouldn't lose engine braking on an axle should one wheel slip. But we can't.

HDC works in reverse too, FWIW.

Totally agree with Gordon re chains in mud. Also, trying to fit the buggers....not very nice! At least snow is just cold!

[disco2hse]

In my view HDC is a waste of time for any trained driver (and yes I'd love an explanation as to why it isn't). All it does is apply the brakes for you, and you can do that yourself. ABS works in low range on the D3, so I'm not seeing any advantage whatosever. HDC is of course only applying the brakes for you and does so to a set speed, it can't see the likes of a washout or spoon drain coming and slow things down more or less depending on the terrain and the manual control isn't as quick to react as foot pressure.

There has been plenty of discussion on these forums about these. Just do a search if you really want that explanation. No one else has said one is better than another. What has been said is that a specific technique is required when using HDC. That was not what the OP was asking for anyway.

Oh, and there are not many "trained" drivers off-road. Are there even many on this forum, you know, that have been formally trained? ;)


One technique that will help is driving through the brakes, ie holding the brakes on with your left foot and applying accelerator to force the wheel to turn slowly. That'll keep the wheels rotating whereas just applying brakes or using HDC is constantly trying to slow the wheel, not force it to rotate slowly. That makes quite a difference.

Umm, frankly. That's a recipe for disaster. No way are the reactions of your one brain going to be faster than the computers controlling the various vehicle functions.

And by the way, that is exactly what HDC is doing. Engine turn wheel, brake control slippage.


Also, HDC can be a little rough and jerky

So? So is the ride on rough tracks.


HDC works in reverse too, FWIW.

Said that. :)

[gghaggis]

The one main advantage I can see with HDC is that it can apply braking to select wheels depending on lock-up - ie it will release/partially release a wheel that has locked up. A driver-controlled braking technique could never enforce that fast enough to make a difference. You can 'drive through' the HDC too, balancing the car between braking and forward momentum with the throttle. This is a technique best done in GGS mode, so that you have greater control over the throttle and diff lock-up.

It's not the solution to _all_ descents, but it can be pretty impressive when used correctly.

Note that the HDC in the 2010 models is much smoother and quite unobtrusive.

Cheers,

Gordon

[rmp]

There has been plenty of discussion on these forums about these. Just do a search if you really want that explanation. No one else has said one is better than another. What has been said is that a specific technique is required when using HDC. That was not what the OP was asking for anyway.


The explanation I was referring to does not exist on this forum.




Oh, and there are not many "trained" drivers off-road. Are there even many on this forum, you know, that have been formally trained? ;)


I wouldn't know





Umm, frankly. That's a recipe for disaster. No way are the reactions of your one brain going to be faster than the computers controlling the various vehicle functions.


You've missed the point. If you are descending a 4WD track chances are the gradient varies and, therefore, so can the braking force applied. The example I gave was a spoon drain where you may be descending quite quickly, but as you come to the relative flat part you can slow down effectively. HDC keeps the vehicle at one speed, like cruise control, and doesn't factor in the changes in terrain. Now yes the HDC speed can be varied, but what's quicker -- changing foot brake pressure or pressing buttons to increment and decrement speed? And if it all goes wrong and you need to come right off the brakes what do you do then? Disengage HDC, re-engage it...change the speed....it's all easier with simply modulating the brake pressure.




And by the way, that is exactly what HDC is doing. Engine turn wheel, brake control slippage.


No. HDC brakes wheels. It does not force them to turn. It sets a maximum speed, not a minimum.




So? So is the ride on rough tracks.


So......all the more reason to be gentle with the controls so as not to induce a loss of traction.




Said that. :)

My apologies.

[rmp]

The one main advantage I can see with HDC is that it can apply braking to select wheels depending on lock-up - ie it will release/partially release a wheel that has locked up. A driver-controlled braking technique could never enforce that fast enough to make a difference.


Which is precisely what ABS does, and in fact HDC is part of ABS. I do not see any difference between the computer applying a given brake pressure, and the ABS system then releasing wheels as required, and a human applying the same pressure, and ABS doing exactly the same. If ABS works differently when in HDC mode I agree HDC then has a point, and it may do for Land Rovers. I don't know but I doubt it, and I know Jeep's system does not differentiate between a human or their HDC.




You can 'drive through' the HDC too, balancing the car between braking and forward momentum with the throttle. This is a technique best done in GGS mode, so that you have greater control over the throttle and diff lock-up.


Interesting tip for GGS, I shall try that. I usually use RC mode on hills as I like my centre coupling locked up nice and tight on gradients.





Note that the HDC in the 2010 models is much smoother and quite unobtrusive.


Agreed, although I would say a driver can still do it better.

[Jamo]

If you are descending a 4WD track chances are the gradient varies and, therefore, so can the braking force applied. The example I gave was a spoon drain where you may be descending quite quickly, but as you come to the relative flat part you can slow down effectively. HDC keeps the vehicle at one speed, like cruise control, and doesn't factor in the changes in terrain. Now yes the HDC speed can be varied, but what's quicker -- changing foot brake pressure or pressing buttons to increment and decrement speed? And if it all goes wrong and you need to come right off the brakes what do you do then? Disengage HDC, re-engage it...change the speed....it's all easier with simply modulating the brake pressure.
.

I agree! I generally found HDC to be more effort in such situations and creaqted clumsier reactions trying to change it's speed and turn it off/on.

HDC might be able to quickly apply the brakes, but it can't read the ground.

[disco2hse]

No. HDC brakes wheels. It does not force them to turn. It sets a maximum speed, not a minimum.

Umm. Read what I said again. I said just that ;)

"Engine turn wheel, brake control slippage."

[gghaggis]

Robert,

The difference is that when you release brake pressure (say a wheel has locked up), you release pressure on _all_ wheels. The HDC releases pressure only on the wheel locked up. I believe this is different to the Jeep system.

Once you've commenced a hill descent with HDC on, you shouldn't need to disengage it. You can still override it with either the brakes or the accelerator. Of course, some descents (the rear-clenching type ones) require slower progress than the HDC can provide, and in those instances you can't just rely on the computer. You need to know how to drive.

Cheers,

Gordon

[disco2hse]

Interesting tip for GGS, I shall try that. I usually use RC mode on hills as I like my centre coupling locked up nice and tight on gradients.

Now you see there is something I cannot agree with. If you are ascending an incline then yes you want to lock diffs so that you do not lose power on individual wheels when they start to lose traction. But when descending an incline you actually want to disperse power in a controlled fashion by allowing individual wheels to turn and find traction as they roll. On a vehicle without HDC you use engine braking and no lockers so that wheels can turn at whatever speed they need to. By locking diffs you prevent that from happening. With HDC, as we have agreed, the brakes are applied individually on the hubs so with lockers on all you are doing is stressing the transmission and excessively wearing brakes.


Agreed, although I would say a driver can still do it better.

As John Dewey said, you cannot win an argument through debating points of difference when one or the other have already made up their mind.

[rmp]

Umm. Read what I said again. I said just that ;)

"Engine turn wheel, brake control slippage."

That's not my point. With HDC to slow the car the brakes are applied. Another way to get the car to move as slowly as it would with HDC is not to brake but to drive the wheels at that speed. This method is less likely to induce a skid.

[rmp]

Robert,

The difference is that when you release brake pressure (say a wheel has locked up), you release pressure on _all_ wheels. The HDC releases pressure only on the wheel locked up. I believe this is different to the Jeep system.


It's the same on the Jeep and all other HDCs I've seen. Yes, when the driver releases footbrake pressure all four wheels get less brake pressure but again -- that's not the point. As ABS works in low range, when a wheel slips the computer will reduce brake pressure on that wheel anyway, exactly as it does for HDC. Therefore, I'm not seeing any value in HDC unless the ABS calibration is somehow different HDC vs non-HDC. Jeep's isn't, I don't know for certain about LR.




Once you've commenced a hill descent with HDC on, you shouldn't need to disengage it. You can still override it with either the brakes or the accelerator. Of course, some descents (the rear-clenching type ones) require slower progress than the HDC can provide, and in those instances you can't just rely on the computer. You need to know how to drive.

Cheers,

Gordon

Yep agreed and I do think HDC systems descend too quickly for many descents, rocky ones in particular. An exception is Toyota's Crawl Control which goes down to 1km/h.

[rmp]

Now you see there is something I cannot agree with. If you are ascending an incline then yes you want to lock diffs so that you do not lose power on individual wheels when they start to lose traction. But when descending an incline you actually want to disperse power in a controlled fashion by allowing individual wheels to turn and find traction as they roll. On a vehicle without HDC you use engine braking and no lockers so that wheels can turn at whatever speed they need to. By locking diffs you prevent that from happening. With HDC, as we have agreed, the brakes are applied individually on the hubs so with lockers on all you are doing is stressing the transmission and excessively wearing brakes.


For those interested in why I suggest lockers in downhill try this exercise; find a steep slope, one so steep you gain a little speed even when locked in first low. Make sure on this slope the vehicle will be cross-axled, ie diagonal wheels in the air. See what happens as the vehicle passes the cross-axle section...it'll take off due the effect of the differential. Then try the same again, but with locked diffs. The difference is remarkable and that is why using lockers when descending is a good idea. Disco2hse, sorry I do not understand your explanation, particuarly "disperse power in a controlled fashion by allowing individual wheels to turn and find traction as they roll."




As John Dewey said, you cannot win an argument through debating points of difference when one or the other have already made up their mind.

I'm not here to win or lose (go to General Chat if you want to score points), I'm here to further my understanding and I like having my views challenged. Gordon's always up for that and it's great to have an intelligent debate without it descending into ill humour. Actually I rather think Gordon and I agree on most things but have a habit of approaching any given topic from entirely different angles so it looks like we're disagreeing ;-)

[gghaggis]

Robert,

Not sure I follow you - ABS doesn't normally activate in low range at the speeds we're talking about? You'd feel it in the brake pedal if it did.

Agree with the diff scenario - RC will give you better control in the situation you're talking about (more-so if you have the rear eLocker). But as it auto-engages/auto-disengages, it will also avoid the loss of control that disco2hse is referring to - best of both worlds :BigThumb:

Cheers,

Gordon

[rmp]

Robert,

Not sure I follow you - ABS doesn't normally activate in low range at the speeds we're talking about? You'd feel it in the brake pedal if it did.

Agree with the diff scenario - RC will give you better control in the situation you're talking about (more-so if you have the rear eLocker). But as it auto-engages/auto-disengages, it will also avoid the loss of control that disco2hse is referring to - best of both worlds :BigThumb:

Cheers,

Gordon

ABS does work in low range, I've had it activate and LR tells me should work in low range. What I don't know is whether the activation calibration is different in HDC, I've never got an answer to that question. That for me is the big question about the effectiveness of HDC.

The rear locker isn't in my experience smart enough to engage in the situation I described and even if it was it'd need to pre-lock, not react, and until LR come out with terrain sensing technology it is not as good in that situation as a manually operated locked. That said I do think the auto locker is wonderful and it allows you to focus more on the line than the diff, just sometimes I'd like it to be manually operable.

[gghaggis]

ABS does work in low range, I've had it activate and LR tells me should work in low range. What I don't know is whether the activation calibration is different in HDC, I've never got an answer to that question. That for me is the big question about the effectiveness of HDC.


I know it activates in low range if you're at speed, but I didn't think it could activate when crawling - there shouldn't be enough of a speed differential to get it to kick in? The traction control module will, and of course HDC. Hmm, I'll have to try it and see.



The rear locker isn't in my experience smart enough to engage in the situation I described and even if it was it'd need to pre-lock, not react, and until LR come out with terrain sensing technology it is not as good in that situation as a manually operated locked. That said I do think the auto locker is wonderful and it allows you to focus more on the line than the diff, just sometimes I'd like it to be manually operable.

If you have the 4wd info screen you'll see it lock the rear as soon as one wheel loses grip, and you'll feel it. Try driving the same steep downhill across wombat holes in both RC and then sand - you'll see the difference, the car won't lurch forward as one wheel comes off the ground.

At least, that's how it should work - it's a bit more sensitive in the 2010 models.

Cheers,

Gordon

[rmp]

OK Gordon, I'll give that a shot. I must admit I've not specifically tested it but as I own another car with a manual locker I know what it feels like (and doesn't) to have a wheel in the air lose grip on an axle downhill. I have no doubt it's better than an unlocked D3.

If the ABS system isn't sensitive enough to operate at low speed then how does HDC do it? It's the same mechanism of a computer looking at relative speeds. Hence my original contention, but being electronic my further query about how, if at all, the calibration is changed. We know the ABS calibration is changed for different TR settings, and in some vehicles it is changed in hi vs low range, so it could well be changed when operating in HDC.

[gghaggis]

If the ABS system isn't sensitive enough to operate at low speed then how does HDC do it? It's the same mechanism of a computer looking at relative speeds. Hence my original contention, but being electronic my further query about how, if at all, the calibration is changed. We know the ABS calibration is changed for different TR settings, and in some vehicles it is changed in hi vs low range, so it could well be changed when operating in HDC.

The mechanical sub-system is the same, but HDC uses different algorithms in determining how to apply/release each wheel. The modules are quite different. Think of it as a completely different 'computer' for each.

Cheers,

Gordon

[rmp]

The mechanical sub-system is the same, but HDC uses different algorithms in determining how to apply/release each wheel. The modules are quite different. Think of it as a completely different 'computer' for each.

Cheers,

Gordon

OK well there's the answer I was seeking. I suspected this but couldn't be sure. How are you so sure of it?

[ADMIRAL]

Check out the June issue of 4x4 Australia. It has a comparison of electronic traction control and mechanical lockers.

They have a D4 without the 'E' diff ( engine size not indicated, but they look like 19" rims, which means a 3.0 litre ), a 200 series and a 76 wagon with mechanical lockers.

[Leo]

Don't forget that the rear locker is pre-loaded to varying degrees depending on which TR mode you've selected. I used to moan about the lack of manual lockers in the D3, but now would never go back.

[gghaggis]

OK well there's the answer I was seeking. I suspected this but couldn't be sure. How are you so sure of it?

Basically from downloading and studying the GTR docs. The D4/RRS 2010 uses the Bosch DF11 ABS module - it has 7 or 8 sub-modules. One of those is dedicated to HDC. One to ETC etc.

We also had a car whose HDC was faulty, however the ABS (at speed) worked just fine.

Cheers,

Gordon

[brad72]

After my 1st dabble into 4wd'ing the other day I have a question regarding the HDC. For the following i was in low range and rock crawl mode. In forward, everything worked fine,descent was controlled, i could vary the speed with the cruise etc. When I went up a steep section forward I got stuck so i eased on the brake, put the car in reverse, let off the brake but even with HDC the car just seemed to be too fast to be safe and HDC didn't seem the same as forward. Was i doing something wrong, was rock crawl the wrong program when the ground was a bit loose, or is reverse just that bit faster.

Thanks

[DiscoWeb]

When I went up a steep section forward I got stuck so i eased on the brake, put the car in reverse, let off the brake but even with HDC the car just seemed to be too fast to be safe and HDC didn't seem the same as forward. Was i doing something wrong, was rock crawl the wrong program when the ground was a bit loose, or is reverse just that bit faster.

Could it also be that everything seems too fast when you are going backwards, :eek:down a steep hill for the first time in your brand new D4 :eek::eek:

Regards,

George

[gghaggis]

After my 1st dabble into 4wd'ing the other day I have a question regarding the HDC. For the following i was in low range and rock crawl mode. In forward, everything worked fine,descent was controlled, i could vary the speed with the cruise etc. When I went up a steep section forward I got stuck so i eased on the brake, put the car in reverse, let off the brake but even with HDC the car just seemed to be too fast to be safe and HDC didn't seem the same as forward. Was i doing something wrong, was rock crawl the wrong program when the ground was a bit loose, or is reverse just that bit faster.

Thanks

I think the default HDC speed in Command 1st (low range) is 3.5kph. It may/may not be the same in reverse, but you should still be able to slow it down (via the cruise buttons) to the same speed as forward. Seeing as you were stuck, perhaps there was just no traction, so the car started sliding downhill? And yes, the feeling of speed is greatly enhanced when you're going backwards!!

Cheers,

Gordon

[rmp]

I think the default HDC speed in Command 1st (low range) is 3.5kph. It may/may not be the same in reverse, but you should still be able to slow it down (via the cruise buttons) to the same speed as forward. Seeing as you were stuck, perhaps there was just no traction, so the car started sliding downhill? And yes, the feeling of speed is greatly enhanced when you're going backwards!!

Cheers,

Gordon

x 2

[rmp]

Basically from downloading and studying the GTR docs. The D4/RRS 2010 uses the Bosch DF11 ABS module - it has 7 or 8 sub-modules. One of those is dedicated to HDC. One to ETC etc.

We also had a car whose HDC was faulty, however the ABS (at speed) worked just fine.

Cheers,

Gordon

HDC would certainly have its own module, and HDC failing wouldn't knock out ABS but it would vice-versa. I suspect the HDC module is a controlling module for ABS like ETC and ESC. Question is whether it controls it in a different way or not relative to the driver. Must try and squeeze an answer out of LR. They do love questions like that ;-)

Anyway this has been an most interesting discussion so thank you for that.

[gghaggis]

It's actually more like the diagram below (taken from one of my seminar slides). Programatically there is an ABS module, under which there are algorithmic sub-sections and sub-sub-sections, one of which is the ABS sub-system (ie the actual ABS algorithmic section is a sub-class under the ABS module - they're two different things).

Cheers,

Gordon

https://www.aulro.com/afvb/images/imported/2010/05/1071.jpg (http://www.aulro.com/app/showphoto.php/photo/17497)

[Dirty3]

After my 1st dabble into 4wd'ing the other day I have a question regarding the HDC. For the following i was in low range and rock crawl mode. In forward, everything worked fine,descent was controlled, i could vary the speed with the cruise etc. When I went up a steep section forward I got stuck so i eased on the brake, put the car in reverse, let off the brake but even with HDC the car just seemed to be too fast to be safe and HDC didn't seem the same as forward. Was i doing something wrong, was rock crawl the wrong program when the ground was a bit loose, or is reverse just that bit faster.

Thanks

Can anyone tell me if I am dreaming, but recently took my new D3 on it's first outing and up a considerably steep climb on smooth clay (std road tyres) the vehicle slowed to a crawl at the crest of a run off, revs slowed, even though I engaged more gas peddle pressure. Then she just took off, like it regained lost traction. I thought afterward, "well that's what it's designed to do" but it was a little disconcerting at the time. Having been used to driving a vehicle and now this thing knows better than me?

[gghaggis]

Smooth clay climb, your DSC was probably activating (even if you had turned it 'off') as the car struggled to find grip and slewed side to side. In this scenario, the DSC will reduce torque to the engine (to prevent you spinning the car sideways), almost to the point of stall if necessary. As soon as it finds grip however, the DSC cuts out and torque is resumed!

Cheers,

Gordon

[Dirty3]

Smooth clay climb, your DSC was probably activating (even if you had turned it 'off') as the car struggled to find grip and slewed side to side. In this scenario, the DSC will reduce torque to the engine (to prevent you spinning the car sideways), almost to the point of stall if necessary. As soon as it finds grip however, the DSC cuts out and torque is resumed!

Cheers,

Gordon

Thanks Gordon, yes I did have DSC turned off (thanks to the useful tips on this forum) but I didn't get any sideways movement, more so when approaching the crest of each section. But it worked a treat, just a bit nerve wracking for the first time. Cheers,
Neil.

[rmp]

That initially sounded like DSC but I doubt it for two reasons:

1. You had it deactivated and while the off switch doesn't truly turn it off it does significantly desensitive it and you have to do something pretty dramatic to kick it in

2. From what you describe I can't see the parameters being met for a DSC intervention anyway -- slow speed, no turning, no slide

So, I suspect it's a more prosaic case of the D3 just being a little slow on the uptake with a gearchange or response to throttle rather than being clever.

[rmp]

It's actually more like the diagram below (taken from one of my seminar slides). Programatically there is an ABS module, under which there are algorithmic sub-sections and sub-sub-sections, one of which is the ABS sub-system (ie the actual ABS algorithmic section is a sub-class under the ABS module - they're two different things).

Cheers,

Gordon

https://www.aulro.com/afvb/images/imported/2010/05/1071.jpg (http://www.aulro.com/app/showphoto.php/photo/17497)

Interesting...going off that model it may be different, assuming the ABS module is merely a control system and has no activation logic or at least not the type in question. Who's to know, I'd like to look at the functional specs for the system ;-)

I would suggest adding the steering wheel angle sensor and pitch sensor as these are also important inputs to stability control. I don't know what EBS is -- a collective term for EBD/EBA? TSC would presumably be another module next to DTC/EBS.

[gghaggis]

I don't know what EBS is -- a collective term for EBD/EBA? TSC would presumably be another module next to DTC/EBS.

Robert,

EBS is the 'Emergency Braking System' - this is a cut-down diagram of the full system, so I haven't included all inputs/outputs.

Cheers,

Gordon

[Signal1]

Love this discussion Gentlemen.

[Dirty3]

That initially sounded like DSC but I doubt it for two reasons:

1. You had it deactivated and while the off switch doesn't truly turn it off it does significantly desensitive it and you have to do something pretty dramatic to kick it in

2. From what you describe I can't see the parameters being met for a DSC intervention anyway -- slow speed, no turning, no slide

So, I suspect it's a more prosaic case of the D3 just being a little slow on the uptake with a gearchange or response to throttle rather than being clever.

Could it be that the wrong terrain response setting was used? I was in Rock Crawl - Logic from previous vehicles, low range up steep climbs, select drive to allow car to decide which gear etc. Would Mud/Ruts be a better choice? I'm open to suggestions here. I know I need a decent tyre....seems that's not such an easy thing either! But I suspect with more grip, maybe the vehicle will be less sensitive? I'm still learning the ropes with this baby.
Neil.

[gghaggis]

Could it be that the wrong terrain response setting was used? I was in Rock Crawl - Logic from previous vehicles, low range up steep climbs, select drive to allow car to decide which gear etc. Would Mud/Ruts be a better choice? I'm open to suggestions here. I know I need a decent tyre....seems that's not such an easy thing either! But I suspect with more grip, maybe the vehicle will be less sensitive? I'm still learning the ropes with this baby.
Neil.

In Rock Crawl you will get more intervention from the system (in terms of cutting back engine power), to the point where it reduces power such that there is no wheel spin before it will allow an increase in engine speed. This can sometimes result in stalling. So yes, for anything that requires speed/momentum, Mud-Ruts is a better proposition. Change to RC only if you can no longer make any forward progress (or, of course, if you're actually climbing rocks).

Cheers,

Gordon

[brad72]

gghaggis, I can confirm this. I had the D4 in grass,gravel,snow on a steep section and the car slipped on the loose dirt till i lost all forward momentum. Stopped, changed to rock crawl and off i went with no issues. She really is a marvelous little computer that controls the wheels and power. Heaven help me if I have to go back to a regular 4x4 and rely on skill:(

Brad