Full time four wheel drive.

Submitted: Thursday, Mar 07, 2013 at 14:30
ThreadID: 100939 Views:2341 Replies:4 FollowUps:24
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Dumb question.
My car (Pajero) has the option of two wheel drive, or full time four wheel drive.
I'm use to either 2wd, or 4wd either high or low.
Whats the benefit with the full time? Never had one before.

Thanks.
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Reply By: Notso - Thursday, Mar 07, 2013 at 14:48

Thursday, Mar 07, 2013 at 14:48
Full time will give you better traction and controll on slippery surfaces eg. wet roads etc. The torque from the drive is transmitted to all four wheels instead of it all going to the rear in 2WD.

Disadvantages would be a slight increase in fuel usage and tyre wear.

AnswerID: 506252

Follow Up By: SDG - Thursday, Mar 07, 2013 at 15:01

Thursday, Mar 07, 2013 at 15:01
Thanks for that. With the amount of cars with them now, I'm assuming this is capable of highway speeds, or should it really only be used at the lower speeds.
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Follow Up By: Notso - Thursday, Mar 07, 2013 at 15:08

Thursday, Mar 07, 2013 at 15:08
Yes, any speed is OK. The older systems had no centre diff and you'd end up with "Axle Wind Up", but the centre diff allows the front and rear axles to rotate at different speeds, as long as you don't lock the centre diff.
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Follow Up By: Member - PJR (NSW) - Thursday, Mar 07, 2013 at 16:09

Thursday, Mar 07, 2013 at 16:09
I have been told that with LSD diffs on the front and rear axles you are really guaranteed of drive going to two wheels only. ie 2wd. Eg when one front and one rear wheel is in slippery mud you could be stuck with all drive going to the two slipping wheels.

Thus if we put a slippery diff in the middle couldn't that mean we could be one wheel drive in the worst case?

Of course this is without locking diffs and traction control.

Phil
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Follow Up By: Notso - Thursday, Mar 07, 2013 at 16:55

Thursday, Mar 07, 2013 at 16:55
The diff can be either locked or unlocked.

With open diffs front and rear and the centre diff locked then you have even torque to both front and rear so if one wheel on each axle has no traction then you are stuck.

If you have LSDs on front and rear it is slightly better as they are only limited slip. If you have diff locks front and rear then as long as one wheel has grip you may get out.
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Follow Up By: Member - PJR (NSW) - Thursday, Mar 07, 2013 at 17:07

Thursday, Mar 07, 2013 at 17:07
Thats what I said. I am aware of that and have seen it.

My question is if you then put a slippery diff in the center to drive the front and rear drive shafts would you then be open to a situation with three wheels slipping and thus only having one wheel drive?

Phil
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Follow Up By: Notso - Thursday, Mar 07, 2013 at 17:21

Thursday, Mar 07, 2013 at 17:21
Within the bounds of the efficiency of the LSDs, and they vary a great deal, then in theory you could have a similar situation to the Locked centre diff, it would depend on how much slip was allowed by the slipperies.
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Follow Up By: Member - PJR (NSW) - Thursday, Mar 07, 2013 at 17:30

Thursday, Mar 07, 2013 at 17:30
Just wondering.

With all the electronics and traction control, that I prefer not to have, it would most likely never happen. Even with the LSDs on the 100 series a touch of the brakes can help. I don't know if it was a fluke bit it did help me once. Beat getting the boots muddy anyway.

Phil
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Follow Up By: Patrol22 - Thursday, Mar 07, 2013 at 19:38

Thursday, Mar 07, 2013 at 19:38
I'm getting a little confused with this thread....could someone please remove the cloud for me please. I'm wondering just how many, if any, 4WDs have an LSD front and rear??? or for that matter in the centre diff. Me, I've never seen these sort of driveline configurations on any vehicle....not saying that they don't exist just that I've never heard/seen before.
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Follow Up By: Ross M - Thursday, Mar 07, 2013 at 20:05

Thursday, Mar 07, 2013 at 20:05
Patrol22
Yes you are right, confused is the correct term.
There is lots of hypothetical anecdotal stuff and a wide range of understanding of what is being asked.

It seems NOT TO BE a full time 4WD at all.
If we new what Pajero vehicle it actually is then we would zero in on what features it actually has.
At the moment we are shooting in the dark especially if the info is what they have heard and don't really know about.

Ross M
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Follow Up By: Member - PJR (NSW) - Thursday, Mar 07, 2013 at 20:15

Thursday, Mar 07, 2013 at 20:15
Guys. I was way off topic. I am sorry. I just asked a simple question About how the four wheels would receive torque if all three diffs were LSD. And as true to form with the internet it has confused and up set folk.

Please feel free to report it to the moderators to be removed.

Besides we have one day to pack before a big club drive in those great Vic High areas.

Cheers

Phil
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Follow Up By: Olsen's 4WD Tours and Training - Friday, Mar 08, 2013 at 13:15

Friday, Mar 08, 2013 at 13:15
Phil,

I don't see that you were off topic. As I see it the questions you asked relate directly to understanding the operation of the Pajero. You have asked very legitimate questions, and the kind of questions that are answered in any good 4WD training course. In fact the Pajero and the Prado provide great material for training.

The problem is that exactly how torque is shared via a differential is actually quite complex and completely unnecessary to understand in detail for most users. The key points are-

- too little torque goes to one wheel in certain circumstances for that wheel to provide force capable of moving the car. e.g. loss of traction at the opposite wheel will result in no drive at the other wheel on that axle (let's describe it as slip between the two wheels on one axle). Limited slip differentials do not solve this problem, because the slip is still there, just limited. LSD is not an off-road tool, it is a traction improvement device that developed out of the rally car and general motor racing games - providing traction out of corners when accelerating.

-The only sure way to get full torque at both wheels is to have a locking differential- hence their popularity. Mind you, that makes turning a corner difficult until you unlock it.

- all full time 4wds have a centre differential, some are limited slip when not locked, some are open when not locked, some are electronically controlled, locking when the management program determines they need to. Locking the centre diff delivers full torque to both drive shafts (the torque is shared between front and back axles).

- In full time 4wd mode without the centre diff locked it is entirely possible to have insufficient torque delivered to 3 wheels- what you describe as one wheel drive. Unmodified Landrover Discovery 2 owners would attest to this.:-)

- Think of the centre diff lock as being the same as a part time 4wd with the selector in 4wd position and the front hubs locked. ie really truly driving both axles -if not all four wheels :-)

The Pajero in contrast to the Prado is most likely set up with the ski-ing and similar markets in mind. It has a centre differential but it also has the option of 2wd, bypassing the centre diff and transfer case altogether.

2wd would save fuel when compared to full time 4wd so that option is available for a market that predominantly drives on sealed roads.

Engaging full time 4wd would provide superior traction in rainy or slushy conditions on sealed roads, such as one might encounter in Japan in winter with no danger of transmission windup as the centre diff allows slip.

Engaging low range will lock the centre differential thus making the car equivalent to a part time 4wd with selector in 4wd position and hubs locked. This is of course for low traction/high torque situations and will result in transmission windup if used on a high traction surface.

By contrast, some Prados seems to be geared towards the towing market among other markets. The ability to engage 4wd low range without the centre diff locked (as available in some model Prados) is a huge advantage when backing trailers, as it allows you to go very slow but does not create transmission windup.

I hope this helps.

David O





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Follow Up By: Member - PJR (NSW) - Friday, Mar 08, 2013 at 14:51

Friday, Mar 08, 2013 at 14:51
Hi David

I was not really interested in any particular vehicle. Just what could happen with "all time FWD vehicles".

I believe you answered my question half way through when you said " In full time 4wd mode without the center diff locked it is entirely possible to have insufficient torque delivered to 3 wheels".

Personally I thought that would be the case. I am familiar with LSD's etc. All good reading. I just didn't want it to run off into a 2WD verses 4WD verses 1WD argument. That's why I did not want to direct my question at any particular model or car.

Thanks for the response.

We are off to the Vic High country now for a weeks trip with the club. They always try to find a track that we cannot get up with the LSDs and no lockers. So far we have beaten them. Wheel placement, a good auto box and tyre pressure adjustments do wonders.

Catchya

Phil
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Follow Up By: mikehzz - Saturday, Mar 09, 2013 at 08:22

Saturday, Mar 09, 2013 at 08:22
My LSD is a great traction tool. It locks the rear axle when one of the wheels slips a little bit more than the other. I don't have any traction control. No more sitting cross axled.
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Follow Up By: Olsen's 4WD Tours and Training - Saturday, Mar 09, 2013 at 12:59

Saturday, Mar 09, 2013 at 12:59
Mikehzz, what vehicle so you drive? That is a pretty impressive LSD if it does that.
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Follow Up By: Notso - Saturday, Mar 09, 2013 at 13:10

Saturday, Mar 09, 2013 at 13:10
Years ago we had a thing called a "No Spin" diff in a rescue truck. If one wheel lost traction it would lock the opposite wheel and let the one without traction go into neutral more or less. Great for slippery spots but frightening at speed!
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Follow Up By: mikehzz - Saturday, Mar 09, 2013 at 23:36

Saturday, Mar 09, 2013 at 23:36
Mine is an 04 diesel Grand Cherokee with a Trac Loc lsd in the rear replacing the open diff. The lsd uses an internal clutch type mechanism that locks the diff when the torque difference to each wheel reaches a certain amount. The friction shims inside only last for about 100,000 kms before they are worn out and slip too much to be of any use I am told. I've heard that Nissan Patrols can have a decent lsd as well and that Toyota's are rubbish in the lsd department. I've had no experience with either, just what I've heard.
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Follow Up By: Olsen's 4WD Tours and Training - Sunday, Mar 10, 2013 at 07:34

Sunday, Mar 10, 2013 at 07:34
Mike.

I am not familiar with the lsd in the jeep, but very familiar with the LSD in the Patrol, as I drive one and maintain it. The amount of torque delivered to the wheel with grip is not a lot compared to a locking differential and is equal to that required to overcome the clutch. How helpful it is depends on a heap of factors, weight of vehicle, rolling resistance, slope, bogging etc etc.

My understanding of the Toyota diff is that it is quite good, but wears quickly compared to the Patrol and therefore becomes less useful.

David O

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Follow Up By: mikehzz - Sunday, Mar 10, 2013 at 07:45

Sunday, Mar 10, 2013 at 07:45
I tried an auto locker (Lokka) in mine first but it kept throwing the sensitive Mercedes gearbox into limp mode on roundabouts. I crossed my fingers and replaced it with the Trac Loc and been very happy. ARB only make an air locker for the front of Jeep Grands. Cheers
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Reply By: NTVRX - Thursday, Mar 07, 2013 at 14:59

Thursday, Mar 07, 2013 at 14:59
Hi SDG, Yep....what notso said.....have a read of your owners manual. There is heaps of stuff you should know about your Pajero in there. The Pajero Club Of Victoria is a website with a good forum (like this one) with very helpful members.
AnswerID: 506254

Follow Up By: SDG - Thursday, Mar 07, 2013 at 15:02

Thursday, Mar 07, 2013 at 15:02
Thanks.
I'm reading the Pajero forum in another window, as for manual, don't have one yet. One is on order.
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Reply By: patsproule - Thursday, Mar 07, 2013 at 16:54

Thursday, Mar 07, 2013 at 16:54
Whenever it's wet, even on tar, drop it into 4H. It makes a huge difference and transforms it from tail-happy to neutral. Same deal on gravel or dirt roads, dry or wet.

And you can engage / disengage up to 100kph. Just move the lever forward as you are driving along, back off the throttle a little and wait for the dash lights to stop flashing.

Pat
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Follow Up By: SDG - Thursday, Mar 07, 2013 at 17:00

Thursday, Mar 07, 2013 at 17:00
I'm guessing it would come in handy next week on the Oodnadatta then.
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Reply By: Ross M - Thursday, Mar 07, 2013 at 19:58

Thursday, Mar 07, 2013 at 19:58
SDG
Unless your Pajero is sold as a FULL TIME 4WD model as is a PRADO and also later Pajeros, you are really talking about a 4wd Pajero which normally runs in 2WD and is changed to driive all wheels ie 4WD as required, so is not a FULL TIME 4wd Pajero.

All Full Time 4WD's have a centre differential which can be locked as required to ensure front and rear axles receive drive torque. These with open diffs are then only 2WD.
If the centre diff isn't locked then it becomes a one wheel drive.

So, by what you have said yours isn't a full time 4WD. This 4WD selection feature is only used on loose or slippery roads and isn't made for sustained use ON road where high tyre grip is happening. Transmission wind up/damage and poor steering and increased tyre wear rate will result if used on bitumen.

Ross M
AnswerID: 506277

Follow Up By: Notso - Thursday, Mar 07, 2013 at 20:25

Thursday, Mar 07, 2013 at 20:25
The Paj he is talking about has the Super Select system which allows it to run either 2WD of full time 4 WD, it has a centre diff, along with a few other smarts.
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Follow Up By: SDG - Thursday, Mar 07, 2013 at 20:42

Thursday, Mar 07, 2013 at 20:42
Correct as far as I can tell Notso.
It has 2H, 4H, 4HLC, and 4LLC.
I think thats how it goes.
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Follow Up By: patsproule - Thursday, Mar 07, 2013 at 21:35

Thursday, Mar 07, 2013 at 21:35
Ross, the Mits Super Select system as fitted from the 1990's onwards is a full-time 4WD capable system. Only a few of the GL models missed out on it. It has a full centre diff in 4H mode and it locks this diff out in 4HLc mode and 4LLc mode. Just like a Prado / 80 / 100 series but you can disconnect the drive to the front if you want. I dont fully agree with your statements re 2 and 1 wheel drive. If all 4 wheels are on the ground the torque is applied to all (when in 4H). Later Super Select also incorporates a viscous coupling across the centre diff in order to provide a slight torque bias towards the rear tending towards 50/50 when worked hard (when the viscous coupling heats up and adds drag). Pre traction control models also used a Hybrid Torsen + Viscous coupling rear diff for similar torque distribution reasons.

Pat
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Follow Up By: Echucan Bob - Saturday, Mar 09, 2013 at 10:45

Saturday, Mar 09, 2013 at 10:45
Pat

I agree. I've had two Pajero's. The first in 1992. The superselect had "full time 4WD" with the option of disengaging the front wheels. The Prado lacked this facility. I did long highway trips in 2H to reduce friction.

Bob
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