Thread: Descent control question

Originally Posted by Franz

These vids have less to do with HDC than with the CDL.

To the best of my knowledge, HDC was not used in either of these situations. What these vids did prove was that a D2 without a CDL was dangerous in these situations. LR thought that TC would eliminate the need for CDL and therefore did not bother to connect it (even though they left the spiggot in up till 2002)

Cheers,

Franz

Yes, but isnt that the point Franz. LR's HDC was meant to be used when the vehicle was going down a steep hill - especially given that there was no CDL to be activated..... Without HDC ON OR CDL locked the vehicle can be run away easily. Going down a steep hill without CDL locked OR HDC on (at the least - clearly better to have both going) is simply asking for trouble - close to chucking in neutral and not touching brake, throttle, handbrake and just letting gravity take over...seriously why would anyone take the time to post those up on youtube...now that I think about it the lady who got LR to do the CDL install didnt have HDC on in reverse from memory...).
Cheers

Originally Posted by ozscott

Yes, but isnt that the point Franz. LR's HDC was meant to be used when the vehicle was going down a steep hill - especially given that there was no CDL to be activated..... Without HDC ON OR CDL locked the vehicle can be run away easily. Going down a steep hill without CDL locked OR HDC on (at the least - clearly better to have both going) is simply asking for trouble - close to chucking in neutral and not touching brake, throttle, handbrake and just letting gravity take over...seriously why would anyone take the time to post those up on youtube...now that I think about it the lady who got LR to do the CDL install didnt have HDC on in reverse from memory...).
Cheers

Not sure I completely agree.

Going forward down a steep slope without CDL engaged is not a problem - I'm not sure what happened in that video. Going down backwards is - as can be seen in the video - the front wheels just lock up and you lose steering control. I think the issue is caused by the unequal drive distribution and the ABS system does not recognise the lock up of the front wheels.

Personally, I rarely use HDC as I have had a scary moment on a scrabbly track where the rear tried to overtake the front. Also, the HDC is too fast for many steeper slopes - The D3 has addressed this by having a variable HDC which can be dialled in from 3.5 kmh.

As for CDL, as soon as I leave the blacktop, I engage it - it's uses are many. HDC, hardly gets used - only when I want to excercise the shuttle valves.

Cheers,

Franz

Originally Posted by Franz

Also, the HDC is too fast for many steeper slopes ........................................

If you find this, either you are doing something wrong, or your HDC is not working. In low gear it will crawl, at no more than walking pace, down the steepest slope, with or without CDL.
As mentioned below, you need to engage HDC just before the steep bit or it can run away if you let it.

Originally Posted by biggin

If you find this, either you are doing something wrong, or your HDC is not working. In low gear it will crawl, at no more than walking pace, down the steepest slope, with or without CDL.
As mentioned below, you need to engage HDC just before the steep bit or it can run away if you let it.

If I'm doing something wrong then I've done it repeatedly in both my Disco's for over 10 years! My HDC definitely works and all Disco2's have a 7 kmh setting for HDC - much too fast for very steep descents - drive a D3 sometime and experience what HDC with a correct setting feels like.

Now a manual performs much better in 1st low range and HDC get used less because of the lower gearing. A D2 auto using HDC and following a manual not using HDC down the hill will catch the manual and try to overtake it.

As far as I'm concerened, if they had deleted the HDC feature from the D2 it would not have bothered me at all.

It should also be said that a smooth, very steep descent is fine with HDC but if the surface is rock strewn and lumpy, 7 kmh is way too fast.

I've been told in the D2, the TC (therefore involving HDC) is biased to be axle dependant; in that the system is not strictly managing 4 wheels independantly rather only whats on the same axle (2). Is that the case? And is this then the reason for reconnecting the CDL? I notice the TC rarely triggers when I have the CDL in.

Originally Posted by Signal1

I've been told in the D2, the TC (therefore involving HDC) is biased to be axle dependant; in that the system is not strictly managing 4 wheels independantly rather only whats on the same axle (2). Is that the case? And is this then the reason for reconnecting the CDL? I notice the TC rarely triggers when I have the CDL in.

Not sure about the answer to your question regarding the axle bias but HDC is controlled by the SLABS computer using wheel speed sensors and when the vehicle speed exceeds 7 kmh all the brakes activate and slow the vehicle down to the set speed.

Originally Posted by Franz

If I'm doing something wrong then I've done it repeatedly in both my Disco's for over 10 years! My HDC definitely works and all Disco2's have a 7 kmh setting for HDC - much too fast for very steep descents - drive a D3 sometime and experience what HDC with a correct setting feels like.

Now a manual performs much better in 1st low range and HDC get used less because of the lower gearing. A D2 auto using HDC and following a manual not using HDC down the hill will catch the manual and try to overtake it.

As far as I'm concerened, if they had deleted the HDC feature from the D2 it would not have bothered me at all.

It should also be said that a smooth, very steep descent is fine with HDC but if the surface is rock strewn and lumpy, 7 kmh is way too fast.

Thanks Franz, I appreciate your feedback, and accept what you are saying.
I have done a bit of study on this and RAVE says that "the SLABS ECU calculates a target speed from the throttle position sensor element of the engine data input".
I suppose then that if the throttle position sensor is not setup precisely, it could target a speed more, or less, than 7kph.
Also, if running larger diameter tyres, then this would increase the speed also.
Just thinking out loud here, trying to work out why you think HDC is too quick.
Next time I will take a bit more notice of how quickly it actually goes.
Good thread all.
PS I would love to try out the D3 one day, but I'm worried that I wouldn't be so wrapped with my D2 after the experience.

The early HDC systems were at a set speed and a tad too fast but manual braking assists here. Also when first engaged they to go a bit faster than set and then retard back to the correct speed.

On my RRS the speed of HDC is variable for as much as 20kph to a slow walk but when brakes are applied or other changes to TR are applied it goes back to the fastest speed. I actually found low range and command shift was far better at keeping the speed down when decending - was also a lot smoother than HDC and a lot less noisy.

The HDC in my 98 Freelander and the RRS are all four channel systems.

Garry