Member Since: 29 Dec 2009
Location: London. Scotland. The Alps.
Posts: 131
Q: Transmission Wind Up on Disco 3
Right - numpty question time.
All Disco3s have a centre diff that locks either fully or partially depending on what you select on Terrain Response, and is fully locked in Rock Crawl mode.
If you select Rock Crawl mode (& low ratio) and drive on tarmac, what will happen? Does the computer automatically slip the centre diff to prevent axle windup, or are you on a path to damaging or breaking your transmission? How would you know it was damaged? Presume there would be a bang of some sort...
I ask as the Disco3 handbook doesn't really provide much information on the topic and vehicle handover certainly didn't go much beyond where the light switches were...
I'd add that the handbook says dont use Lo ratio for normal road driving...but doesn't make any attempt to explain why.
Just interested !
Thx
M.
Last edited by mikeyp on 13th Sep 2010 3:22 pm. Edited 1 time in total
13th Sep 2010 3:00 pm
roveribis
Member Since: 04 Apr 2009
Location: Puerto Rico
Posts: 132
Hmmm... I would venture to say that the computer can tell there is no wheel slipage, and would adjust accordingly.
(obviously, should never purposely do this...)-------------------
2008 LR3
ARB bumper, winch, sealed Snorkle, dual battery, Rover Specialties sliders, whole car custom skid plates, 33" tires, ARB air compressor, CB radio, etc...
13th Sep 2010 3:04 pm
crwoody
Member Since: 09 Mar 2009
Location: Littleborough
Posts: 2109
To run in "rock crawl" you have to select low range also, otherwise the centre diff remains open.
While you could drive in low range on tarmac, you won't go very fast and even then the centre diff only locks when the car thinks it needs to so I don't think any bangs would be forthcoming.
Having said that, I can't imagine it's the sort of thing you would do by accident and not notice.Clive
13th Sep 2010 3:19 pm
mikeyp
Member Since: 29 Dec 2009
Location: London. Scotland. The Alps.
Posts: 131
Thats good info, thx, but where did you get this info from (not doubting you, just interested in reading more). What can I read that tells me more about how the Disco 3 trasnmission works? Is there a LR Technical Overview or decent third party book? The handbook is next to useless in this regard...
13th Sep 2010 3:25 pm
crwoody
Member Since: 09 Mar 2009
Location: Littleborough
Posts: 2109
Info gained from pressing buttons, responding to messages and watching the "4x4 info" display screen.
TBH, I don't know of any technical literature on the subject, though I'm sure it must exist somewhere, there are however far more knowledgeable members on here who may be along shortly. Clive
13th Sep 2010 3:39 pm
PaulP
Member Since: 04 May 2007
Location: Barcelona
Posts: 4317
As crwoody says, the centre (and rear e-diff if fitted) will not lock unless it needs to.
It will however be subjected to varying amounts of "pre-loading" meaning that it will come into operation earlier or later depending on the Terrain Response mode selected and obviously the amount of wheel slip it detects on any of the wheels.
I'm pretty sure it says in the manual that no damage can occur by driving in the wrong TR mode irrespective of the terrain, so don't worry about it.
It could be interesting to hoon it around a roundabout in Rock Crawl low range and see what happens though 2006 Discovery 3 TDV6 SE AutoBuckingham Blue 2007 Golf GT DSG
13th Sep 2010 3:55 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26704
The D3 will not wind up its transmission, as previously said, the centre diff is pretty clever. However, things can and do go wrong with gearboxes.
My friends Range Rover Classic has just failed spectacularly. It had a BW Viscous coupled transfer box (with no selectable diff lock) When the viscous bit seized, the first he knew was when the front prop snapped at the universal joint by the gearbox. The flaying propshaft then proceeded to smash the floor pan, and rest of the gearbox to bits
So, in about 20 years time when the D3 is getting old, and things start to sieze up, this is what might happen
13th Sep 2010 8:01 pm
wvlenthe
Member Since: 07 Jan 2009
Location: Arnhem
Posts: 1967
Gareth wrote:
The D3 will not wind up its transmission, as previously said, the centre diff is pretty clever.
Hi, this here is the devil's advocate...
No matter what surface, especially with pre-locked differential, when a wheel slips, the slip is immediately stopped for traction purposes, right?
Slip would be defined as 'one wheel spinning faster than the other' right?
So what happens in a tight corner? 'One wheel spins faster than the other'.
OTOH, even in rock crawl, there's a limited slip allowed, judging from all the Youtube vids. So your diffs will prob not suffer from a slight corner as the diff will be released once you go straight again. Staying in a tyre-rubbing corner might be a different story, but that's deliberate misuse.
Could also be that the D3 takes the steering angle into account in calculating wheelspin, after all the angle is displayed in 4x4 info. So clever a car, LR must have thought of this.
(I'll wait for someone reporting how they've done before I try though!)
regards,
WiljoD3 V8 HSE Auto in Zermatt silver - driveway version gone but not forgotten, only the living room cupboard version remains
13th Sep 2010 9:11 pm
Iain G
Member Since: 31 Jan 2009
Location: Filey
Posts: 430
My experience of the centre diff operating is that there has to be quite a significant 'spin' on the wheel with no traction before the centre diff comes into play. Far more than would be experienced by negotiating a tight bend.
13th Sep 2010 10:09 pm
Iain G
Member Since: 31 Jan 2009
Location: Filey
Posts: 430
A bit of info I have in my possession:
The DD295 transfer box is a full time, permanent four-wheel-drive unit, with 50/50 torque distribution to the front and
rear driveshafts. The unit is manufactured by Magna Steyr Powertrain in Graz, Austria and supports the following
features:
ô€º Permanent four-wheel-drive with a bevel gear centre differential, providing a 50:50 torque split
ô€º Selectable high and low range for optimum on-road and off-road performance
ô€º Two-speed, fully synchronized 'shift-on-the-move' system allows the driver to change the range without
having to stop the vehicle
ô€º Electronically controlled multi-plate clutch providing a centre differential lock and torque biasing function to
give improved traction performance and vehicle dynamic stability.
A strategy, to electronically control the centre differential multi plate clutch assembly, has been developed to provide:
ô€º a pre-loading function, increasing locking torque with increased driving torque
ô€º a slip controller to increase locking torque under off-road conditions and decrease locking torque for optimum
comfort, e.g. parking.
The unit is located under the vehicle and is mounted on the cross-member, behind the transmission. The unit is
identical for all engine derivatives.
The transfer box receives a torque input from the transmission output shaft, which is passed through the unit to two
outputs for the front and rear drive shafts.
The input torque is equally distributed via a bevel gear type differential. In order to provide an optimal torque
distribution to each wheel in all driving conditions, the unit is equipped with an electronically controlled locking and
torque-biasing device. This device detects wheel slip via various vehicle system inputs to the transfer box control
module and locks the differential accordingly. The locking torque is applied through a multi-plate clutch assembly.
A planetary gear set, located in the differential assembly, allows the driver to select high or low range whilst driving,
this is known as 'shift on the move'. When in low range, the planetary gear set provides a ratio of 2.93:1, which gives
the vehicle an extremely low crawl speed for off road driving and trailer towing. High range is a direct drive from the
transmission output shaft and provides a 1:1 ratio.
Both the centre differential locking and biasing and the 'shift on the move' features are actuated via a DC transfer box
motor, which is controlled by the transfer box control module, via a Pulse Width Modulation (PWM) signal.
13th Sep 2010 10:12 pm
ukdave104
Member Since: 31 Jul 2007
Location: Stonehaven
Posts: 266
Great write up Iain G, now we should all know how it works
2014.5 Discovery 4 HSE in Corris Grey Metallic - arriving this week.
2011 Range Rover Vogue 4.4 TDV8, now departing
2012 Freelander HSE SD4 Auto - Mrs UkDave104's Toy.
2010 Discovery 4 XS - gone
2008 Discovery 3 HSE - gone
2007 Freelander 2 GS TD4 - gone
14th Sep 2010 8:32 pm
Iain G
Member Since: 31 Jan 2009
Location: Filey
Posts: 430
erm, I didn't actually write it
17th Sep 2010 7:57 pm
CFB
Member Since: 02 Dec 2005
Location: Bradford, West Yorkshire
Posts: 6100
Sshh, take the credit 8)2020 BMW X1 18d XDrive X-Line Auto
17th Sep 2010 8:00 pm
mikeyp
Member Since: 29 Dec 2009
Location: London. Scotland. The Alps.
Posts: 131
The Feb 2011 issue of Land Rover Owner International has a v good article on the DD295 Transfer Box. See Pages 180 - 185. Now I can study this a bit more and try and get my head around sun & planet gears. Boy thats going to be a headache....
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