When I put my rr into low range mode, engage Hill decent control and the drive it forward it starts making some horrible crunching type sounds which I can also lightly feel through the steering wheel. If i disengage HDC and continue in a forward motion it is smooth and nice. Anybody any ideas what this may be please ?

just a hunch but I think it's your ABS system operating on the wheels for controlling the descent rate. You normally only use this on a down hill. Perhaps if you are using it on the level the system cant feel it going fwd adn so activates the system.

As I say, knowing the system and without seeing or hearing it myself, I would think it is this.

Alternatively it could be your low range not engaging fully (there is a lot of info here on this - use search, your friend)

Ok Ill get it on a decent slope and try again. I have had it going downhill on a steep but short decline not so long ago with zero issues. As well as it being my own personal roller coaster in slow motion there was no crunching sounds then

Just as a side note we tried the same operation 'on level ground' in my friends rr sport and there was no crunching sounds, just nice and smooth

HDC does indeed crunch

Its the HDC!!!

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Mustard wrote:

Ok Ill get it on a decent slope and try again. I have had it going downhill on a steep but short decline not so long ago with zero issues. As well as it being my own personal roller coaster in slow motion there was no crunching sounds then

Just as a side note we tried the same operation 'on level ground' in my friends rr sport and there was no crunching sounds, just nice and smooth

HDC works completely differently when there is plenty of grip

When there is little grip, the HDC comes into it own

so I am correct in assuming that the HDC crunching away on level ground is normal ? Or indeed just crunching away is normal ? Im a little paranoid here as I dont like the noise / feeling it is doing

I used it downhill on a steep Tarmac slope... It is a very weird noise indeed... Crunchy  Alcohol and eBay is never a good mix

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Ok so I tested the HDC on a serious decline tarmac track, it sure made its crunchy sounds to begin with but then they went away and the rr drove me down the hill as it saw fit, very nice

I pressed the go faster pedal and the crunchy noises began again and got worse as i lifted off the pedal then went away so this leads me to ask the question are you meant to press the accelerator when your in HDC low range mode or just leave it to drive itself ?

Mine works like this, the crunching seems to happen when you use the accelerator. I think HDC is for situations where you wouldn't use the accelerator it's for going down very steep slopes safely, I find just engage it and leave it to the car - no brake no accelerator, still a bit of racket as I think it uses the ABS in some way. Geoff

Dont use the accelerator with hdc engaged, it is for descending slopes at a constant rate and that is about walkimg pace. This is regulated by the car.

When descending a steep slope, activate hdc and take feet off both pedals.

Try to go faster and the abs is activated......

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+1

i'm sure it explains that in the manual.. ... - .- -.




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HDC should be thought of as like an extreme ABS that does the work for you , approach steep decent , engage HDC and descend hill with feet away from the pedals and disengage at the bottom . You can adjust your speed with the cruise control up and down buttons but I can't remember when this was introduced . 2008 MY Supercharged
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