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Old 24th September 2014, 20:10   #271
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by mallumowgli View Post
Duster is a AWD vehicle. It has 3 modes. 2WD, 4WD Auto and 4WD lock.
2WD - Only front axle are powered
4WD Auto - The rear axle engages if front wheels lose traction.
4WD Lock - The rear axle engaged permanently until car crosses 60Kmph

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Originally Posted by mallumowgli View Post
4 WD Auto is an AWD mode I think, with the 4WD lock being locking the central differential
Sorry, there is no center differential in Duster. Let me repeat, the purpose of center differential is to allow 4WD on tarmac or hard surface. Duster doesn't have that feature.

Check the 4x4 system of Duster if you are not convinced: http://www.awdwiki.com/images/nissan-x-trail.jpg
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Old 26th September 2014, 11:38   #272
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Samurai View Post
That is it for now, if this is understood, I'll explain further in later posts.
Alright, since there is no doubt about this, let's move on.

A 4WD vehicle with open center differential becomes helpless if even one wheel loses traction. We have already established this. In this regard, it is no different than regular 2WD vehicles. Therefore, very few 4WD vehicles offer open center differentials. Most drivers of 4WD SUVs simply expect their vehicle to pull out of slushy situations. Open center differential won't meet that requirement. However, limited slip center differential will solve this problem. Since LSD allows different torque on either side, one wheel losing traction won't result in other side losing torque.

That is why most 4WD SUVs offer one of the following 4WD system.

1) Part-Time 4WD without center differential. (eg. Jeep, Gypsy, Gurkha, Endeavour, Scorpio, Thar, Safari)
In these vehicles, once 4WD is engaged they should not be driven on hard surface. It can result in transmission windup.

2) Part-Time 4WD with limited slip center differential (eg. Pajero with Super Select II)
These vehicles can be driven on hard surface even after engaging 4WD. The center differential will ensure no transmission windup will occur, by allowing different speeds. The limited slip (torque-slip) will allow different torque for front and rear prop shafts. That means if any one of the front wheels lose traction, it won't rob the torque from the rear wheels. The center LSD can be locked on demand to behave exactly like Part-Time 4WD without center differential.

3) Part-Time 4Wd with on-demand AWD (Duster, XUV, etc)
These vehicles are pretty similar to part-time 4WD without center differential. Except that 4WD engages automatically whenever lose of traction is detected in the powered wheels. The 4WD will disengage automatically if all wheels have traction. The coupling is usually of the type (viscous/clutch pack) that allows different speeds, so there is no fear of transmission windup. Here the lock refers to permanent engagement of 4WD, but it is still the limited slip type.

4) Full-Time 4WD with limited slip center differential (Grand Vitara, Fortuner)
These vehicles are always on 4WD, but using a limited slip center differential. The center differential will ensure no transmission windup will occur, by allowing different speeds. The limited slip (torque-slip) will allow different torque for front and rear prop shafts. That means if any one of the front wheels lose traction, it won't rob the torque from the rear wheels. The center LSD can be locked on demand to behave exactly like Part-Time 4WD without center differential. But this should be avoided on hard surface, to avoid transmission windup.

That is about center LSD. If this is understood, next I will address the front/rear differentials.

Last edited by Samurai : 27th September 2014 at 10:32. Reason: Correction
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Old 26th September 2014, 11:56   #273
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Default Re: Driving all four wheels: how is it done?

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Alright, since there is no doubt about this, let's move on.
Thanks for your posts. What about Storme, Thar and Scorpio? In which category they will fall?
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Old 26th September 2014, 12:03   #274
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Default Re: Driving all four wheels: how is it done?

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Thanks for your posts. What about Storme, Thar and Scorpio? In which category they will fall?
The first category, I added them to the list.
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Old 26th September 2014, 12:40   #275
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Default Re: Driving all four wheels: how is it done?

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The first category, I added them to the list.
Thanks Samurai for all the details. Could you please educate us on the types of axles like Banjo and Salisbury? Yesterday during the launch of the Scorpio somebody mentioned that they have moved to Banjo type from the previous Salisbury type and that it can carry a lot more load. Is this true?
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Old 26th September 2014, 15:30   #276
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Default Re: Driving all four wheels: how is it done?

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Could you please educate us on the types of axles like Banjo and Salisbury?
Not really familiar with these. I won't be able to tell you anything you can't find on Google.
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Old 26th September 2014, 21:49   #277
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Default Re: Driving all four wheels: how is it done?

Just reporting a correction. In my morning post #272, I accidentally attributed prevention of transmission windup to limited slip, instead of the center differential in point (2). Then I copy pasted the error to point (4). But the eagle eyed DBHPian SS-Traveller point out the obvious error. He also pointed out that on-demand 4WD vehicles have viscous/clutch pack type coupling, and the lock is still limited slip type. It is now corrected.

Last edited by Samurai : 27th September 2014 at 10:33.
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Old 26th October 2014, 14:06   #278
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Default Re: Driving all four wheels: how is it done?



Someone who is entirely clueless about the difference between AWD/4WD and difflocks!
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Old 27th November 2014, 17:13   #279
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

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Dear Eric - lovely photographs, excellent information, completely true and every single thing that you have pointed out is known for a long time, so thanks!
For those of you who STILL wish to dispute the rather obvious short-comings of the Scorpio mHawk VLX 4WD, I would like to refer you again to B.D.'s post #32 in this thread. Can there be any question that B.D. is in complete agreement with Eric (RINGOISM) on this matter?

Auto transmissions also give some degree of protection from drivetrain "windup" in 4x4 vehicles (without center diffs) as the mechanical connection between front and rear axles is lacking. The auto transmission takes up the friction between axles turning at different speeds....to a point anyway. That being said, I would rather drive a MT....it's more manly and tends to awe de womens.

Last edited by DirtyDan : 27th November 2014 at 17:17.
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Old 27th November 2014, 21:43   #280
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

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Originally Posted by DirtyDan View Post
For those of you who STILL wish to dispute the rather obvious short-comings of the Scorpio mHawk VLX 4WD, I would like to refer you again to B.D.'s post #32 in this thread. Can there be any question that B.D. is in complete agreement with Eric (RINGOISM) on this matter?

Auto transmissions also give some degree of protection from drivetrain "windup" in 4x4 vehicles (without center diffs) as the mechanical connection between front and rear axles is lacking. The auto transmission takes up the friction between axles turning at different speeds....to a point anyway. That being said, I would rather drive a MT....it's more manly and tends to awe de womens.
Hi Eric, I think you have mentioned my name in your post by mistake. As those words were posted by our beloved Bawa Ji and not by me.

The post #32 is by BD and not by me.
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Old 27th November 2014, 22:05   #281
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

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Originally Posted by DirtyDan View Post
Auto transmissions also give some degree of protection from drivetrain "windup" in 4x4 vehicles (without center diffs) as the mechanical connection between front and rear axles is lacking.
??

Regards
Sutripta
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Old 28th November 2014, 02:18   #282
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

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Originally Posted by Sutripta View Post
??

Regards
Sutripta
Yeah, I mis-wrote. What I should have said is that some of drivetrain windup is taken up by the torque converter of an automatic transmission because of the viscous coupling. And, no, I am not going to try to explain that. Go ahead if you want to.

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Hi Eric, I think you have mentioned my name in your post by mistake. As those words were posted by our beloved Bawa Ji and not by me.

The post #32 is by BD and not by me.
I am not Eric.

I never said you wrote post #32.

B.D. really is B.D.

You really are Mary Jean Johnson from Cedar Falls, South Dakota and your favorite color is red.
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Old 28th November 2014, 03:09   #283
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

Fluid coupling, not viscous coupling.
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Old 28th November 2014, 11:28   #284
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Sutripta, DD is correct. The fluid coupling which reduces engine braking also allows slippage between front and rear axles to reduce bind up.
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Old 28th November 2014, 20:09   #285
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Default Re: Scorpio VLX 4x4 Review: 1000 kms in Lahaul-Spiti

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Originally Posted by 4x4addict View Post
Sutripta, DD is correct. The fluid coupling which reduces engine braking also allows slippage between front and rear axles to reduce bind up.
Just to establish context, we are talking of

Quote:
Originally Posted by DirtyDan View Post
Auto transmissions also give some degree of protection from drivetrain "windup" in 4x4 vehicles (without center diffs) as the mechanical connection between front and rear axles is lacking. The auto transmission takes up the friction between axles turning at different speeds....to a point anyway.
Quote:
Originally Posted by DirtyDan View Post
What I should have said is that some of drivetrain windup is taken up by the torque converter of an automatic transmission because of the viscous coupling.
aren't we? (Essentially Scorpio 4X4 manual vs auto)
I didn't know this, and would never have guessed!

Regards
Sutripta

PS.- I still don't get it. If someone could please explain ...
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