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Mr Andrew
Member Since: 28 May 2007
Location: Sydney, Australia
Posts: 128
  
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| Torque restricted when stuck? |
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Two cases I have experienced where the D3 did not seem to have the torque at idle to get onto boost and then make progress...
1: one wheel in a deep hole (so resting on wishbone), other three on good tractive ground, although the whole show was on a slight downhill. In low range reverse, my mates car would not deliver enough power to drag out. I never understood it, but have since experienced case 2 following...
2: A D2 was pulling a disabled RR Classic (rear diff failure) up a steep, loose hill. The D2 lost traction, so the tow failed. We attached my D3 to the front of the train, to share the load of the RR. Low range, 1st gear, rockcrawl mode, DSC off, throttle depressed... not much happened - I was very surprised. No spinning wheels, no progress, engine just did spooled up to maybe 1100? rpm and stayed there. Car did not feel very happy. I stayed on it, and then the D2 made a a tiny bit of progress, my revs picked up, and the D3 started grinding up the hill, at maybe 1800 rpm and pulling very strongly.
So, two questions - does this make sense? Is there some type of torque limit thing somewhere in the drivetrain? Or it is simply thet the motor, at low revs off boost, does not have the torque to get on top of the extreame resistance in 1st low range, when really stuck? If it is a rpm/boost/torque thing, any ideas how to drive around it? I later thought of using 2nd (to allow more slip), or using Sand mode, but didn't think of it at the time to test the theory.
Anybody else have a similiar expeirnce to share, or a solution? Thanks!
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 27th Jul 2009 1:34 pm |
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Ken
Member Since: 20 Feb 2006
Location: Here
Posts: 10865
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Yeh its your bottle jack stuck to the wishbone
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| 27th Jul 2009 2:10 pm |
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Bushwanderer
Member Since: 27 Nov 2007
Location: Northern Rivers, NSW, Australia
Posts: 2050
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Hi Mr Andrew,
I think it's a matter of driving style, where you are starting off at too low engine revs to allow the turbo to spool up. Peak torque is at and above 1900 rpm, therefore noticing the change at 1800 is about right.
HTH,
Peter The Bearded Dragon
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| 28th Jul 2009 3:36 am |
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JR
Member Since: 23 Jul 2009
Location: Cape Town
Posts: 76
 
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| Re: Torque restricted when stuck? |
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Mr Andrew wrote:I later thought of using using Sand mode
Sand mode would probably have delivered the extra drive from the jump that Rock Crawl does not. The difference in throttle response between the two modes when in LR 1, is not significant, but rather just enough to mess with ones ego... 
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| 28th Jul 2009 6:57 am |
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Mr Andrew
Member Since: 28 May 2007
Location: Sydney, Australia
Posts: 128
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Peter,
If you are stuck (ie, immobile), how do you change your driving style? I was reluctant to take up the slack on the tow strap with momentum (it was a tow, no a snatch), and in the first, the car was immobilised. Does change your driving style mean pulling in into gear with revs already aboard?
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| 28th Jul 2009 11:15 am |
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JR
Member Since: 23 Jul 2009
Location: Cape Town
Posts: 76
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Mr Andrew, I've just had a thought 
Not to question you, or your ability, but how certain are you that the DSC was indeed off? Because what you're describing sounds a lot like it may have re-engaged without you noticing...
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| 28th Jul 2009 4:24 pm |
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stapldm
Member Since: 11 Sep 2006
Location: Swine Town
Posts: 2330
 
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Does DSC not re-enable automatically when you change TR mode? Dr. Ian Malcolm:
"Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."
Transgenic tomato anyone?
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| 28th Jul 2009 6:13 pm |
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Donald
Member Since: 15 May 2007
Location: Inverness
Posts: 188
 
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Mr Andrew,
in case 1 was "your mates car" an auto or manual? Reverse towing ie parking heavy trailers uphill has a history of cooking clutches - so perhaps it was starting to glaze and gave up the ghost? They sometimes recover if you stop soon enough and let it cool, although long term you will need to replace it.
Case 2 Do you really want full throttle starts when you are rock hopping on 3 or 4 foot boulders? Terrain response mode rock crawl will change the throttle response to a soft long travel, the diffs will be loaded near to locking if required, cross car suspension will be doing its best to keep the car level.DSC will be at its max in terms of controlling traction control, ABS etc. The car's systems would be working against what you were trying to achieve.
Grass, gravel,snow mode, DSC off, low range 2nd gear would have given a more suitable start with the power coming on smoothly as the car gained momentum,changing up to third if auto.
Sand mode would give higher revs in whichever gear you had chosen, holding the change points for longer.
HDC would be preselected of course - you did consider what to do if you failed the hill climb with two other cars roped to you?
Donald Chipped, K&N, tow pack, AT2's, Mantec, fridge in boot, invertor, Garmin, laptop/Memory Map, Optima yellow top, Traxide Kit, Phillips Extreme bulbs
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| 28th Jul 2009 8:47 pm |
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Bushwanderer
Member Since: 27 Nov 2007
Location: Northern Rivers, NSW, Australia
Posts: 2050
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Hi Mr Andrew,
Unfortunately, with a manual it means feathering the clutch in order to keep the revs high enough for the turbo to be operating (and being in as low a gear as possible). Horrible thought, isn't it. 
Best Wishes,
Peter The Bearded Dragon
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| 29th Jul 2009 2:48 am |
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Mr Andrew
Member Since: 28 May 2007
Location: Sydney, Australia
Posts: 128
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Thanks all for the thoughts and comments, but I am not really any clearer about it.
In both cases, cars were auto TDV6's. So interesting clutch comments, but not applicable here. When I assisted the heavy tow, definately had DSC off. In the earlier, grounded reversing case, I cannot say DSC was off so emphatically, but the driver was a savvy D3 owner, and we tried lots of options - including turning car off, locking it, waiting a few minutes as a reset. I suspect DSC off was one that we tried, but it was a while ago. Did not make any difference.
Donald, interesting thoughts, but I must have missed something 'casue I can't follow how they apply. I rarely use HDC - low range & modest ABS modulated brake pedal is rarely a problem, although on very slippery downhills HDC is better. In any case, not sure how HDC is relevant to an uphill tow - individually any of the cars could breeze up the hill (or hold still on the brakes, so no tumbling back down), but the tow load of disabled RR changed the situation. Obviously there were drivers in all three cars.
Grass/gravel/snow - maybe, but the notion of building momentum was the problem - there was no movement at all, at least for the first say 15 seconds. So we're talking all 4 wheels, with good traction, not rotating at all, and seemingly insufficent torque from the TDV6 to doing anything about it.
Other than the obvious (ie, using my hidden winch), how else would people suggest you deal with this situation? Surely I haven't reached the limit of the usually infinitely capable D3?
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| 31st Jul 2009 12:33 pm |
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Bushwanderer
Member Since: 27 Nov 2007
Location: Northern Rivers, NSW, Australia
Posts: 2050
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Hi Mr Andrew,
As you didn't specify and your D3 is listed as a manual, you can understand my comments. However, as they were autos, forget everything I said. 
Nonetheless, the principal is the same, you need to keep the revs high enough to allow the turbo to operate (assuming a TDV6). The torque converter then acts similarly to the clutch in a manual. Again, you would ideally be in low range and "command select" (manual control).
If you have terrain response, select the appropriate one, and THEN disable DSC. Remember that DSC will re-enable if the ignition is turned off or if the terrain switch is shifted to a different setting.
HTH,
Peter
PS: I don't think it's likely in your scenarios, but if the TDV6 is not up to temperature, it WILL NOT operate effectively. The Bearded Dragon
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| 1st Aug 2009 7:45 am |
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Donald
Member Since: 15 May 2007
Location: Inverness
Posts: 188
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Hi Mr Andrew
sorry for the late reply - I was abroad for a few days.
My comments regarding rock crawl mode is that the ECUs for engine and gearbox are designed to prevent the full throttle response available in other modes.
From your comment that the D2 lost traction, I took that to mean by the severity of the climb,or low level of friction available from the loose surface as opposed to a possible wrong gear selection. No offence intended.
In my mind I envisioned a 2.5 ton RR with a further 2 ton D3 tied to the back of your 2.7 ton D3 when all three of them reached the limit of grip. Or if only the dead RR and the D2 loss grip could the D3 pull or hold both?
An intresting senario to control and co-ordinate safely - communication between drivers, possible no engine to give servo assist for the RR etc.
I've had experience of a Defender towing a D2 on a trailer and a D3 towing another D3 on a trailer both failing a hard steep hill climb and much appreciated the HDC helping control the descent.
Like you, I normally just select low first to third as appropriate unless I am training but I do preselect on climbs.
Donald Chipped, K&N, tow pack, AT2's, Mantec, fridge in boot, invertor, Garmin, laptop/Memory Map, Optima yellow top, Traxide Kit, Phillips Extreme bulbs
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| 4th Aug 2009 10:09 pm |
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