Hill decent and slippery stuff

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Originally Posted by rmp

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.

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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.

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Originally Posted by rmp

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.

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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

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.

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Originally Posted by rmp

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.

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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

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Originally Posted by gghaggis

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

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

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.

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.

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Originally Posted by rmp

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

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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

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

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Originally Posted by brad72

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.

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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

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Originally Posted by 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

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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