Hill descent control and diff locks.

[KeithB]

Will pushing the hill descent control button do anything useful when going down a steep off road hill with front and rear lockers engaged? I have never tried it out of fear of breaking something or at least confusing the electronics. I have an LC 200 diesel.
Keith

[Watty2975]

Hey Kieth,
It works pretty well. I have tried it a couple of times on some short steep hills. It was nice and controlled. Tried the same hill using just low range and the brakes. Hill decent was better!

[KeithB]

Watty, was that with the diff locks on?

[GBC]

It works off the abs. You won't break anything with the lockers in.

[cruiser 91]

Only engage rear lockers when descending.
Engage front and rear lockers when ascending.
Edit: because you have air lockers you can turn off front locker prior to cornering 

[#jonesy]

I think the question is if the hill decent works off the ABS and from the few times I've seen it used it alternates the braking around the wheels, applying brakes to only 1 wheel on the same axle, what will happen.

[#jonesy]

I think Cruiser just answered it

[scblack]

I think the question is if the hill decent works off the ABS and from the few times I've seen it used it alternates the braking around the wheels, applying brakes to only 1 wheel on the same axle, what will happen.

The hill descent control will not work as effectively as it could have. It wont break anything - just not work as well as it could. As you say hill descent brakes each wheel independently, or allows power to each wheel. If the axle is locked the process may be compromised, due to drive pushing to a wheel the system is trying to brake.

During descent you would not be using accelerator much I suppose, but the two systems could be somewhat counter-acting each other.

[tombie]

Only engage rear lockers when descending.
Engage front and rear lockers when ascending.

Exactly.... front locker will skew the vehicle when descending.

Rear Locker only when descending and HDC will enable control with steering.


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[Hoyks]

As said above, the Hill Decent Control works in a similar way to ABS, in that if there is any difference between how quickly the wheels are turning, then it applies braking force to the wheel that is turning fastest (as that one is probably in rolling contact with the ground) to slow you up.

With a cross axle diff lock engaged there should be no difference in the rotation of the wheels, so the HDC will see it as everything is hunky-dory, and shouldn't engage, on that axle anyway.

The other question is; Are they factory diff locks? I know with the Mazda, using the diff lock causes a few systems like stability and traction control to shut down, so it may be worth reading the owners manual to see if it is likely to make the computers do anything funky.

But, No, I don't think there is any risk of breaking anything by using diff locks and HDC.

[KeithB]

Yes Hoyks,
It's the same on the LC200. Stability Control goes off when you lock the centre diff. The system doesn't know about the ARB lockers.
I am guessing, having read all of the posts, that if the front, rear and centre diffs are locked the HDC (or the stability control for that matter) won't be able to detect if one wheel is slipping in relation to the others. So how can it do anything?

[tombie]

Because it will detect over-speed and try to brake the vehicle to slow it down..


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[Watty2975]

Watty, was that with the diff locks on?

Keith, it was with the centre diff lock on.

[KeithB]

Yes,
I always have the centre diff lock on in rough country. And, contrary to advice in these posts, I will use the front locker (rightly or wrongly) if the the descent is down a dead straight track. Mind you, I am usually towing a camper, which changes the dynamics a bit.

[cruiser 91]

Keith mate!!!!!!!!!!!!!!!
Golden rule when using ARB air lockers front and back with centre diff lock on, high or low range regardless if towing or not.........(I have the centre diff lock mod)
Please see my previous reply post.
I have been taught by a professional and ARB also use this rule, it works...................
There are plenty of Youtube tutorials explaining this rule.
It is hard to go against what feels abnormal until you practice the right way.
Everyone goes through the same..................once you practice the correct way...........it becomes a revelation then a doh! moment, then you feel like a professional 4wder 
The only different application with towing is you may have to operate the camper brakes manually instead of using the the vehicle brake.
Having said that, I'm only experienced in a petrol cruiser and I don't use vehicle brakes what so ever in a decent.
 
 

[tombie]

If you're not willing to learn why bother asking..


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[cruiser 91]

If you're not willing to learn why bother asking..


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Easy there tombie...................its hard to go against what feels right when its not, been there done that 
Its sort of like "when the penny drops" moment 
 

[tombie]

Easy there tombie...................its hard to go against what feels right when its not.
 

My apologies for sounding blunt. But wow!

How can a fully locked up front feel right?
Steering is horrible when locked, if the trailer shoved the vehicle off line it would be nigh on impossible to steer back into position.
Even without a trailer if it starts to turn it will be hard to control.. potentially, dangerously so.

With HDC, rear locked he has the best of all worlds.
Controlled descent speed, vehicle trying to pull straight from its rear diff and steering capability with braking.

Doing otherwise is folly..


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[cruiser 91]

My apologies for sounding blunt. But wow!

How can a fully locked up front feel right?
Steering is horrible when locked, if the trailer shoved the vehicle off line it would be nigh on impossible to steer back into position.
Even without a trailer if it starts to turn it will be hard to control.. potentially, dangerously so.

With HDC, rear locked he has the best of all worlds.
Controlled descent speed, vehicle trying to pull straight from its rear diff and steering capability with braking.

Doing otherwise is folly..


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Absolutely correct!!!!!!!!!!!!!!!!
But when the mind of the unconverted says otherwise, its hard to convert to the correct way until the "penny drops" 
 

[achjimmy]

....(I have the centre diff lock mod)

Hey cruiser if your talking the ability to lock centre diff in high? The 200s have this standard.

[achjimmy]

The 200 has a fantastic traction control system. I'd be doing as advised above as the TC on the front will add an extra level . Worth keeping in mind the 200 has a claimshell aluminum front diff and it's not the best housing for a front locker, personally I choose not to bother as the TC is so good but each to their own.

[cruiser 91]

Hey cruiser if your talking the ability to lock centre diff in high? The 200s have this standard.

No I'm not. Not sure why I added that into the mix.
The centre diff lock mod is the ability to turn on and off the centre diff lock manually at will when in low range.
 

[GBC]

If you're towing in country where in low 1st you are constantly overrunning the HDC you'll melt the axle grease out of the front end in 2 minutes flat relying on HDC only. I'd happily put on both lockers and use the brakes (yes, brakes) as well to help out the HDC on a steep descent. The front end absolutely smokes up in that sort of terrain with a trailer pushing against HDC only. Lockers prevent the same run away that HDC/TC does by maintaining drive (or engine braking) to the wheel with traction. I am a big fan of electronics but we've proven a few times on various vehicles that they don't cope with that sort of abuse for long - you need to help it out with all your tricks.

[tombie]

Again just use the brakes NOT the Front locker...

Brakes And low 1st on a decent rig will more than hold it back.

The front locker engaged will just hinder correct vehicle control...


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[scblack]

This is a question that may depend on vehicle and HDC systems involved.

I just bought an Amarok TDi 420 auto so I'll stick to that. Amarok does have a rear diff lock too.

This is about towing a camper downhill.
Camper has electric brakes of course run by the car - VW dealer supplied electric brakes, 12pin. Amarok does operate anti-sway systems on trailers but my Swan Outback does not have anti-sway fitted.
If I engage the OffRoad mode, which incorporates HDC that obviously operates brakes etc on the Amarok - does that engage the trailer brakes? I assume not, but thought I would put up the question.

If I press the car brakes, that will of course engage the trailer brakes, but will that confuse the HDC systems?

Am I best to manually press the electric brake button to lightly brake the camper? Hopefully this method would be less likely to confuse the HDC system.

I guess I have to get out and test them together, but hopefully I can gather some more info from this topic. My thinking is for driving off-road with camper is the following:
 - Engage OffRoad mode (HDC).
 - Use tiptronic to hold 1st gear.
 - Use electric brake manual button to lightly brake camper.

Depending on steepness - should I engage rear diff lock?