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Old 24th August 2009, 13:01   #1
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Default Center Differential and LSD in SUVs

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Originally Posted by Samurai View Post
Fulltime 4WD is a freaking boon on bad roads, twisters and rains. I have a fulltime 4WD, so I can speak by experience on this one. Fortuner has central diff with LSD which is a pretty expensive part, Pajero and Captiva don't have it, yet are lot more expensive.
The Pajero has 2wd, full time 4wd, 4wd with center diff lock, and low range 4wd with the center diff locked. It therefore has a fourth option, in addition to the three that the GV and the Fortuner have. The 2wd option helps reduce fuel consumption and road noise. Btw, the Pajero also has LSD on the rear wheels.
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Old 24th August 2009, 13:14   #2
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Originally Posted by Sawyer View Post
The Pajero has 2wd, full time 4wd, 4wd with center diff lock, and low range 4wd with the center diff locked. It therefore has a fourth option, in addition to the three that the GV and the Fortuner have. The 2wd option helps reduce fuel consumption and road noise. Btw, the Pajero also has LSD on the rear wheels.
I just checked the Pajero brochure to make sure. Let me repeat, Pajero doesn't have center diff with LSD, only fulltime 4WD have that. Center diff with LSD is very expensive part. And yes, it is lockable in both Fortuner and GV in 4H as well as 4L.

The difference is simply this. You can drive Pajero on 4WD on regular highway only with open central diff, but not in locked position. The Fortuner/GV have an edge because of the LSD in central diff.

Last edited by Samurai : 24th August 2009 at 13:18.
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Old 24th August 2009, 14:40   #3
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Originally Posted by Samurai View Post
I just checked the Pajero brochure to make sure. Let me repeat, Pajero doesn't have center diff with LSD, only fulltime 4WD have that. Center diff with LSD is very expensive part. And yes, it is lockable in both Fortuner and GV in 4H as well as 4L.

The difference is simply this. You can drive Pajero on 4WD on regular highway only with open central diff, but not in locked position. The Fortuner/GV have an edge because of the LSD in central diff.
Samurai:

Sawyer is correct. Pajero 2.8 Super Select 4WD System has an All Wheel drive mode with a lockable Center differential. It also has LSD at the rear just as the Fortuner. One advantage this system has over the Fortuners is that it can be driving in rear wheel drive mode only for fuel efficiency.

If you don't mind the drop fuel efficiency, Pajero 2.8 can be driven in AWD mode all the time. This set up will be the same as the Fortuner. Just to clarify the Pajero 2.8 Does have a Lockable Center Differential and LSD in the rear diff. Pajero 2.8 with Super Select 4WD can be driven in the following modes:

1. Rear Wheel Drive only
2. 4 Wheel Drive with Center diff open. This is essentially AWD mode similar to Fortuner. This mode can be used on any surface. there will be no damage to the 4WD system due to the center diff.
3. 4 Wheel Drive mode with Center Diff locked. This is to be used only in slippery conditions like the part time 4WDs without the center Diff.

But this will all mean nothing since only the die hard Pajero fans who refuse to see that technology has advanced beyond 115 bhp IDI engines will buy the Pajero at a 3.5 lakh premium over the Fortuner.

The Pajero 2.8 and the Endy will have to be either discontinued or repriced. I also feel that after the initial furor does down, Toyota will launch a cheaper version without 4WD and possibly with the 2.5 D4D engine. This will be targeted at the 2.5 Endeavour with 2WD.

Last edited by 4x4addict : 24th August 2009 at 14:47.
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Old 24th August 2009, 15:05   #4
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Originally Posted by 4x4addict View Post
Sawyer is correct. Pajero 2.8 Super Select 4WD System has an All Wheel drive mode with a lockable Center differential. It also has LSD at the rear just as the Fortuner. One advantage this system has over the Fortuners is that it can be driving in rear wheel drive mode only for fuel efficiency.
Well, it is not mentioned in the website. But if you know it for sure (and you know 4WDs well), then I concede the point.
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Old 24th August 2009, 15:25   #5
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Quote:
Originally Posted by Samurai View Post
I just checked the Pajero brochure to make sure. Let me repeat, Pajero doesn't have center diff with LSD, only fulltime 4WD have that. Center diff with LSD is very expensive part. And yes, it is lockable in both Fortuner and GV in 4H as well as 4L.

The difference is simply this. You can drive Pajero on 4WD on regular highway only with open central diff, but not in locked position. The Fortuner/GV have an edge because of the LSD in central diff.
I don't know which Pajero brochure you are looking at. The one I have, as well as the car I own and have driven for over a year now, says otherwise! And there is no such thing as a LSD in the central diff in any car I have come across till now. The Pajero has a LSD, on the rear axle.
You can drive the Pajero in 2wd, which is the normal driving mode on regular highways, for best FE, or in 4wd with the center diff open, or in 4wd with the center diff locked. The last, if you want to wreck the car in a hurry. The 4th mode is the 4wd low, with center diff locked. Which can also wreck the car if used on tarmac.
PS: Since we are on the subject, the two modes with the center diffs locked are for where there isn't strong traction for the tyres, so that the pressures when the two axles want to rotate at different speeds on turns results in traction loss and not driveline stress, wind up and fracture. And this caution applies to all 4wds that have a lockeable center diff, or those that do not have a center diff like the jeeps/gypsies.

Last edited by Sawyer : 24th August 2009 at 15:33.
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Old 24th August 2009, 16:56   #6
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Originally Posted by Sawyer View Post
I don't know which Pajero brochure you are looking at. The one I have, as well as the car I own and have driven for over a year now, says otherwise!
Sawyer, I didn't check to see whether you owned it. But I didn't take your word seriously based on the way you explained the various 4WD modes. That is perfectly fine if you are not offroading. However, 4x4addict knows 4WD very well, so I can take his word that Pajero has central LSD.

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Originally Posted by Sawyer View Post
And there is no such thing as a LSD in the central diff in any car I have come across till now. The Pajero has a LSD, on the rear axle.
Once you pull your foot off the mouth, check on LSD in the 4WD section. Let's not go off-topic here.

Last edited by Samurai : 24th August 2009 at 16:57.
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Old 24th August 2009, 17:02   #7
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Originally Posted by Samurai View Post
Sawyer, I didn't check to see whether you owned it. But I didn't take your word seriously based on the way you explained the various 4WD modes. That is perfectly fine if you are not offroading. However, 4x4addict knows 4WD very well, so I can take his word that Pajero has central LSD.

Once you pull your foot off the mouth, check on LSD in the 4WD section. Let's not go off-topic here.
. Maybe another post from 4x4addict is warranted!
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Old 26th August 2009, 07:18   #8
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Originally Posted by lamborghini View Post
- Was confused by one thing, how can they have an all time 4WD, and then provide a manual shifter as well? How does it work and is it harmful to the engine?


However, the fortuner got to my heart in a way the Innova never can!
Not sure which of the two sticks you are referring to here, but I will take a stab at answering. The usual stick does the usual thing in a manner identical to the Innova. The shorter stick handles the three 4wd modes, which you have to select manually. In some other cars called all time 4wds, these move to 4wd automatically, via a hydraulic pressure sensing transfer case that only activates 4wd if the 2 driven wheels start spinning. And switches it off when they get traction again, and unless that has a lock function, there is no driver involvement in that decision making. I drove a car of that kind for a few years, and never really off roaded with it, and I sense it must have run in 4wd mode for less than a total of 15 minutes in all of those years. If that.
I recently saw a CRV with this kind of drive in slush and it looks a little weird, to be honest. The front wheels are driven all the time ordinarily, and they spin, and then the rear wheels get drive. When that happens, the front wheels stop spinning, and as that happens, the rear wheels lose drive and all the drive shifts back to the front wheels. When the fronts start spinning again....and so on. I can imagine it must be quite unnerving for the driver. I have read articles to the effect that the all time 4wd makes the car very good on twisties, but given how I have seen the thing work, I can't quite see how that can be the case. These kind of 4wds are found in soft roaders, so that the 4wd tag can be attached to them, for a cost lower than installing the kind of 4wd that the Fortuner has. The benefit of the automatic systems also is that the typical driver of those cars cannot damage the car by ignorance of 4wd operating priniciples. The Fortuner can be so damaged, all the way to a fractured drive line, if the wrong mode is selected. So using the Fortuner does need a grasp of 4wd operating principles.
with you about the head/heart. More than anything else, I think the Fortuner pricing reinforces the outstanding value that the Innova is, but it is a car that does not have pose value.
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Old 26th August 2009, 08:41   #9
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I found the following info in the Toyota brochure about the 2 levers and the different 4WD's
I have enclosed pictures
Attached Thumbnails
Center Differential and LSD in SUVs-toyota-fortuner-screen-1.jpg  

Center Differential and LSD in SUVs-toyota-fortuner-screen-2.jpg  

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Old 26th August 2009, 08:57   #10
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Re the last page of the brochure attached - why oh why can they not say against HL - To be used in conditions offering poor traction only??!!! The way it is worded, people will think, if some traction is good, more is even better, let me use it just to be safe! Hopefully, it is clarified somewhere in the manual. Very few of the sales staff has any clue about this either.
This is the most common mode that results in driveline damage. Even in the rains on tarmac, given how well modern tyres stick to tarmac in the rains.
The LL description is just as misleading, but in practice it does not matter, people never leave their cars in LL for long enough to do serious damage.
Btw, the Pajero has exactly this set up with one addition. Below the H would be a 2H, driving the LSD equipped rear axle only. For better FE and less noise relative to its 4H mode.

Last edited by Sawyer : 26th August 2009 at 08:58.
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Old 26th August 2009, 09:35   #11
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Quote:
Originally Posted by lamborghini View Post
- Was confused by one thing, how can they have an all time 4WD, and then provide a manual shifter as well? How does it work and is it harmful to the engine?
Your confusion is understandable. Most people who own 4WD vehicles, don't really understand how it all works. Even the Mahindra & Maruti service stations where I service my CJ340 and GV, the mechanics don't understand the exact usage of 4WD system. It took me more than a year of 4WD ownership, regular offroad experience and frequent discussion with fellow offroaders and 4x4 section to get a decent understanding of just my vehicles.

Since Fortuner 4WD system appears very similar to my Grand Vitara, that is torque sensing LSD in the central diff, let me dare to assume I understand it.

H mode - This is used for your regular driving. Here the front and rear diffs are open. The torque is sent almost equally to both front and rear drive shafts. However, the center differential has torque sensing type limited slip system. It acts as open diff until some lack of traction is detected. When that happens, more torque is sent to the drive shaft with higher traction. The amount of torque is decided by the torque bias ratio. Downside, if the traction is zero in the front or rear, the other side gets nothing either*. Then it is time to lock the center diff.

HL mode - This basically disables or locks the center LSD, this is the normal 4WD high mode in Jeeps. Both front and rear get same torque irrespective of slip.

LL mode - Same as HL mode but you will get almost twice the torque in every gear at half the speed. Generally used for descent control and slow climbing.

N mode - All wheels will be disengaged from the transfer case. Useful for towing only, never engage this lightly. If the vehicle is towed by traffic cops in normal fashion (lifting one side), your vehicle will be severely damaged.

*The clutch based or viscous type LSD behaves differently under similar conditions, but that is off-topic here. When to use the modes can only be understood by frequent offroad driving. Yes, it is possible to damage the system in HL & LL modes, exact explanation is again off-topic here.

If this is all confusing, don't worry. I took a year of hob-nobbing with experts and offroad driving before the basic understanding sunk in.
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Old 26th August 2009, 12:51   #12
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Quote:
Originally Posted by lamborghini View Post
- Was confused by one thing, how can they have an all time 4WD, and then provide a manual shifter as well? How does it work and is it harmful to the engine?
The car is always in Full Time 4WD/All Wheel Drive mode. The second lever is to used to lock the center diff and to engage low range.

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Since Fortuner 4WD system appears very similar to my Grand Vitara, that is torque sensing LSD in the central diff, let me dare to assume I understand it.
Samurai, if I may correct you , The 4WD system with the Torque Sensing LSD in the center diff was developed by Borg Warner and initially came on the Isuzu Trooper. It used to be called Torque on Demand (TOD) in the Isuzu Trooper. This is heavy duty All wheel drive sytem that can be driven in 2WD mode, and will engage 4WD when wheel slip is detected. This Borg Warner system is available in a number of American SUVs.

Mind you the Grand Vitara sytem is a full fledged center diff and can be driven in full time AWD mode.

The clutch pack based part time system found in the CRV/Captiva etc are light duty ones that are meant to provide some traction when wheel slippage is detected. The clutch pack generates heat when engaged and hence it is never meant to used in full-time 4WD mode like the Pajero/Fortuner/Land Cruiser, etc.

For example in the 4WD CRV, the car typically runs in Front Wheel Drive mode. There is a skinny shaft that goes into the rear differential with an integrated clutch pack. This clutch/Rear diff is engaged in three modes:

1) When are accelerating from stand still. This is to reduce torque steer and wheel slippage when you are moving from stand still.

2) When slippage is detected. It shuts off soon as the ECU senses that the wheels are no longer slipping. However an ECU obviously has limits as Sawyer has mentioned about the CRV he saw.

3) Locking the diff with the VTM-4 lock on the dash. This is used to extricate yourself when you are stuck in Sand or slush. Soon as you reach about 16 mph, the ECU shuts off the VTM-4 Lock since it is never meant to be used permanently.

The Pajero and Fortuner doesn't have the Torque Sensing Center Diff. In All wheel drive mode there torque distribution is maintained at 50% front and back.
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Old 26th August 2009, 13:26   #13
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Originally Posted by 4x4addict View Post
The Pajero and Fortuner doesn't have the Torque Sensing Center Diff. In All wheel drive mode there torque distribution is maintained at 50% front and back.
Tini, I got that from here: Fortuner
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Old 26th August 2009, 13:46   #14
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Right at the time I though I understand 4x4 completely.

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H mode - This is used for your regular driving. Here the front and rear diffs are open. The torque is sent almost equally to both front and rear drive shafts.
Is this not the 4x4 high in our jeeps? With the front and rear shaft engaged and open differentials?

Quote:
However, the center differential has torque sensing type limited slip system. It acts as open diff until some lack of traction is detected. When that happens, more torque is sent to the drive shaft with higher traction. The amount of torque is decided by the torque bias ratio. Downside, if the traction is zero in the front or rear, the other side gets nothing either*. Then it is time to lock the center diff.
Why a star * there? Does that means that it has got only one differential in the center and no more at rear and front axle?

Quote:
HL mode - This basically disables or locks the center LSD, this is the normal 4WD high mode in Jeeps. Both front and rear get same torque irrespective of slip.
Is this mode basically locking the diffrentials and not the shafts, as that is already connected?

Sorry if I sound silly...
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Old 26th August 2009, 14:24   #15
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Originally Posted by 4x4addict View Post
The Pajero and Fortuner doesn't have the Torque Sensing Center Diff. In All wheel drive mode there torque distribution is maintained at 50% front and back.
Don't know exactly how the center diff on the Fortuner works, but on the SS II equipped Pajeros, it employs a viscous coupling unit to achieve a 33/67 front rear distribution in normal conditions. Or so I read, it's not easy to make out the difference between that and a 50/50 split in driving a car. Once you lock the center diff, then both axles get equal power of course.
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