Home > Puma (Tdci) > Puma Centre Diff Lock Max Speed? |
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Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2633 |
I suggest you go do the Land Rover Experience course. |
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15th Sep 2010 5:10am |
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AndrewS Member Since: 10 Apr 2007 Location: Hereford Posts: 3707 |
I have up to instructor level 130's have feeling's as well you know |
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15th Sep 2010 3:50pm |
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Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2633 |
And you are telling ppl not to engage CDL off tar? |
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15th Sep 2010 5:41pm |
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JoostKenya Member Since: 31 Jan 2010 Location: Naivasha Posts: 9 |
That change in tyre road friction from tarmac to gravel is exactly the situation in which switching the diff lock can potentially make it dangerous. Especially if you start braking! If your front wheels are almost locking while approaching the gravel the front axle will start transferring a brake torque to the rear axle which could affect stability when cornering. This is also why ABS and stability control systems don’t like a fully locked differential. The drive line will disturb brake forces and lateral tyre forces.
In general I would say, if the road surface is nice smooth and gravel all the way, no problem to lock. If the surface is changing all the time, better not to lock. Driving 60, 70 or 110 doesn’t make any difference for the vehicle behaviour. The only difference at 110 the safety margin is much smaller because you have to react much quicker if things get instable. There was a quote “all available drive could go to the wheel that is easiest to turn”. As a vehicle dynamics expert I don’t know the words “available drive”. I only know things like drive torque, longitudinal or lateral drive force, tyre slip or rotating velocity. I was trying to explain that with all the diffs open the drive torque from the engine is approximately the same on all four wheels. Unlocked the drive torque will definitely not go to one wheel. This is because of the design of a differential. The wheel with the lowest friction coefficient and load is going to spin first at the same drive torque as the other wheels (it is going to run at a higher slip). This is restricting the drive toque to all wheels. Usually this is not affecting stability very much because the lateral tyre force will usually be very low as well. Anyway if you drive already 80 in a high gear the Puma engine does not have enough power to spin a wheel. Even not on snow and ice. Look at all those modern drive trains with active differentials, electronic diff control ( Audi+ Haldex, BMW X6, WRC rally cars) . They are made for maximum traction and stability. But the active control of their diffs is not about locking a diff. Full mechanical lock would be unpredictable in terms of the amount of torque transferred from one wheel to the other. The approach for those vehicles is more about putting a certain percentage to a specific wheel. Please know that an open diff has 50/50 torque distribution. With a locked diff the torque distribution is related to the tyre grip on the road at a specific wheel. It is difficult trying to explain stability of a vehicle without being technical but maybe you can imagine that if things are getting dependent on a factor from outside the vehicle (road surface) vehicle stability is at risk. Another reason not to lock your diffs at higher speeds: Our Defenders have the benefit of full time four wheel drive. We should not try to imitate the inferior driving of all those Toyotas and Nissans with part time four wheel drive isn’t it? Maybe this is why some drive training instructors tell you to lock?? If somebody can give me a reason and technical explanation why to lock I would be really interested. Joost Joost Defender 110 Puma 2.4 Tornado TD5 Racer Defender 110 V8 Defender 136'' 300Tdi Safaricar SIIA V8 Hybrid |
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16th Sep 2010 7:28pm |
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AndrewS Member Since: 10 Apr 2007 Location: Hereford Posts: 3707 |
Am I I dont think so 130's have feeling's as well you know |
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16th Sep 2010 7:37pm |
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Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2633 |
Not exactly - on most of the Jap brands, 4WD mode is equivalent to Defender with CDL locked. Although a Defender is touted as full-time 4WD, you can get stuck if one wheel loses traction I think David128 explained very well the benefits of having the CDL locked off tar - that's exactly how the LR instructor explained it to us during the LRE course. Also, with CDL unlocked, if you happen to go airborne on a gravel road, you run the very high chance of flipping over when the last wheel touches the ground - as happened to a friend of mine. |
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16th Sep 2010 7:42pm |
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custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20292 |
This is going to sound the most thick thing ever to you lot but because I'm fairly new to the Land Rover world and never needed to use DL how do you select it? I have only used high and low box a. to keep things running smooth and b. because i wanted the crawl ability
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16th Sep 2010 7:59pm |
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jst Member Since: 14 Jan 2008 Location: Taunton Posts: 7992 |
the lever that you are pushing fwd to engage low can also be pushed across to the left to engage the CDL. you can do this in high, neutral or low and on the move. If engaging CDL on the move then you should be travelling at a constant speed in a straight line. Cheers
James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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16th Sep 2010 8:48pm |
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custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20292 |
Cheers I looked it up in the manual although it wasn't greatly helpful on this topic. It did however say not to engage difflock from neutral |
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16th Sep 2010 9:55pm |
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Naks Member Since: 27 Jan 2009 Location: Stellenbosch, ZA Posts: 2633 |
that's odd, LR instructor told us to engage CDL when driving in a straight line, clutch in and then push lever to the left. |
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17th Sep 2010 7:17am |
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Setok Member Since: 16 Jan 2009 Location: Helsinki Posts: 419 |
Yes, but this is also much less likely to happen as drive is distributed to all wheels which, I believe, leads to less torque per wheel (correct me if I'm wrong here) for the same movement. With many of the Japmobiles the front wheels are not helping to drive the vehicle at all, only turn it, so the rear wheels are left to deal with all the power. |
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17th Sep 2010 8:27am |
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jst Member Since: 14 Jan 2008 Location: Taunton Posts: 7992 |
you can engage it in neutral, high or low. Cheers
James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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17th Sep 2010 8:31am |
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custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20292 |
Hmmmm, I can't understand why the manual says that then
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17th Sep 2010 10:53am |
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Ricky Chianese Member Since: 15 May 2009 Location: Perth Posts: 10 |
Jooste
Have I opened a can of worms with this thread? Well I suppose my original question about the difflock and speed has been answered; the banter has raised more questions and interesting reading though! So what is your opinion ?: On a reasonable dirt road at say 80Km/hr, is it better to have CD locked or unlocked? With CD locked, in theory, there will be less wear on the CD but somewhat reduced stability in some situations. I suppose landrover may be more worried about driveline wear than stability for warranty reasons. If this is so, it helps explain the CD use instructions in the manual. What's your take on this? Why do today what you can put off until tomorrow? |
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17th Sep 2010 1:35pm |
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