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Old 31st August 2009, 08:12   #61
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That does not matter, because if you let the steering wheel be, this self corrects. Wind only starts with steering inputs for the axle to turn. Also, center diff lock does not have any impact on how the wheels on each axle turn. To impact that, the axle diff lock has to come into play. Not relevant in a GV.
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Old 31st August 2009, 08:27   #62
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When the wheels turn unevenly, it does have impact on the drive shaft. After all, open differential is like an adding device. Does power steering allow for self correction, I wonder, I am not so sure.
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Old 31st August 2009, 08:43   #63
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Yes power steering does allow for this - if you do not fight the wheel. The problem with it is that it does the hard work for you, and that makes your intervention of starting or holding a turn a lot easier. In 4wd center diff locked mode, a non power steered car would be very hard to drive on tarmac, when it comes to turns. Even at medium speeds. At low speeds it would be a monster to turn. You would feel the strain through the wheel, and you could win, but with noticeable effort, that ought to warn a 4x4 savvy driver. A power steered car will insulate you from this, it magnifies your effort. But anything multiplied by zero is zero, so if you can keep your hands off the steering wheel all the time while the CD is locked, no issues of wind up.
Before some one jumps in on reading just this one post, the last sentence needs clarification! I do not mean hands off the wheel each time you lock the CD. Or while it is locked! Consider the drive shaft as a pipe, one end is the tyre gripping the road, the other end is your hand holding the steering wheel welded to this pipe. If the axles turn at different speeds, on turns, the pipe is under torque. As are the other two ends, the one attached via the axle to the road wheel/road, and the other to the steering wheel/your hand holding it. If both ends are stronger than than the middle, torque will fracture the middle. But if the road end is not able to take the torque because the road is slippery/slushy, the tyre contact will yield before the torque can impose fracturing pressures on the middle of the pipe. And locking the CD will not cause wind up.

Last edited by Sawyer : 31st August 2009 at 08:55.
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Old 31st August 2009, 09:46   #64
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Quote:
Originally Posted by Sawyer View Post
A 100 metre run in each mode, once in a month or so, is essential to keep that part of the car in good shape, via use of it.
...one does not have to go into 4wd country to do that, a stretch of open tarmac where you can do this by the side of the road.
If you drive the car with the center diff locked, on hard tarmac, without touching the steering wheel, wind up cannot happen.
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Originally Posted by Samurai View Post
Well, it can happen if the hard tarmac is not perfectly smooth. If the road contains potholes and uneven undulations, one wheel can turn less or more than the other.
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When the wheels turn unevenly, it does have impact on the drive shaft.
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Originally Posted by Sawyer View Post
...if you can keep your hands off the steering wheel all the time while the CD is locked, no issues of wind up.
Uhh... looks like I ended up provoking a difference of opinion here - sorry guys, but I'm inclined to agree with Samurai. Transmission windup will happen on hard tarmac to some extent, however small, in centre diff locked mode (or where no centre diff exists), whether or not there are steering inputs. Main reason here is the different diameters of the front and rear tyres - due to different degrees of wear, different tyre pressures, different brands of tyre etc.

Whether that windup is harmful in the long run may be a matter of debate. Before the gears strip off, before the propellor shafts or drive shafts deform, before the U-joints break, the first victim of even slight windup will be the gearbox synchronisers.

It doesn't take too much effort to find a dirt/muddy track in this country to use locked centre diffs or just 4WD mode once a month to keep the system in working order. Why use tarmac at all?
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Old 31st August 2009, 09:53   #65
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Sawyer, I have a simple question. If right wheel turns a little more than the left wheel from going into a pothole or undulation, do you think it will have an impact on the drive shaft?

PS: You don't need undulation, if one wheel is less inflated than the other, that would do it.

Last edited by Samurai : 31st August 2009 at 09:57.
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Old 31st August 2009, 10:09   #66
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Quote:
Originally Posted by Samurai View Post
Sawyer, I have a simple question. If right wheel turns a little more than the left wheel from going into a pothole or undulation, do you think it will have an impact on the drive shaft?

PS: You don't need undulation, if one wheel is less inflated than the other, that would do it.
If I may answer this... the answer is NO. A difference in rotation between left and right wheels is taken care of by the differential mounted on that particular axle. The difference in rotation between the drive shafts to the front and rear differentials is evened out by the centre differential. So, for front tyres inflated at 28 psi and rear tyres inflated at 32 psi, the average rotation of the rear drive shaft will be less than the average rotation of the front drive shaft (since diameter of front wheels is less than dia. of rear wheels due to the air pressure difference).

In a situation like the one on the Gurkha, where front and rear diffs can be locked individually, the answer to your question would be YES - on hard tarmac.
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Old 31st August 2009, 10:22   #67
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We are talking about the situation where the center diff is locked and front/rear diff is open.

If left wheel turns more than the right wheel due to road undulation, will it impact the front drive shaft?
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Old 31st August 2009, 10:55   #68
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Quote:
Originally Posted by Samurai View Post
We are talking about the situation where the center diff is locked and front/rear diff is open.
If left wheel turns more than the right wheel due to road undulation, will it impact the front drive shaft?
The rotation of the front drive shaft is the same as the rotation of the front wheel which is rotating the most (in a given ratio).

If the rear drive shaft rotates the same number of turns while driving over a given distance as the front drive shaft when the centre diff is locked, then - no effect.

If the rear drive shaft rotates a different number of turns than the front drive shaft - yes, windup happens.

Irrespective of whether front or rear diffs are open, the centre diff being locked will transmit a windup action on the front and rear propellor/drive shafts, the CD and the gearbox - but not on the axles connecting the wheels to the front/rear diffs.

If front/rear diffs are locked, and there is NO centre diff (as in the Gurkha) the windup builds up on the front/rear diff gears, the axles, the front and rear drive/prop shafts, and the gearbox.

If front and rear diffs are locked, but the centre diff is open (don't know what car this can be done on), no windup happens on drive/prop shafts or gearbox - only the axles and the front/rear diffs (whichever is locked) suffers.

All this is for a situation of driving on hard tarmac where an individual wheel cannot slip/skid and relieve the windup.

I hope that explains things. But I thought you are one of the OTR gurus, Samurai.
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Old 31st August 2009, 11:44   #69
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Reading the last few posts still leave me thinking that my fundamentals are ok! And when I do give the 4HL and the 4L modes a work out on tarmac, it is an untrafficked road very close to home. And in 4HL mode, I don't touch the steering wheel, and I don't get out of first. Ditto for 4L. For about 100 metres each. I am pretty sure the Pajero can take that, indeed, I still think no wind up is created at all, when it is driven in that fashion on decent tarmac.
But the point is not this academic subject of why do this on tarmac when one can go to a slushy back road.
The point is, if you are ascending or descending steep tarmac in anger, and you are able to do this in a straight line, should you slip the clutch while ascending, and forego the huge advantage that the low range gives you? Going by the opposite view, that is being recommended by SST/Samurai, clutch slip will have to be resorted to. Or the climb will not be attempted. While coming down, engine braking advantages of 4l will be foregone.
I would not hesistate to use 4l on steep tarmac either ascending or descending, if I was able to obtain a straight route that would allow for use of that mode, without providing any steering input. The one time I needed it but resorted to clutch slip was when I had to climb out on steep and winding narrow tarmac, and had to stay in 4H mode, open CD.

Last edited by Sawyer : 31st August 2009 at 12:04.
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Old 31st August 2009, 12:03   #70
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SS-Traveller, I am no guru, but I did know the answer to my question. I was only trying understand Sawyer's point of view.

All said and done, open differential is a mathematical device, or an algebraic equation with 3 variables. If any one variable changes, the other two or one variable has to change to compensate for it. If one wheel turns faster while the other wheel remaining at constant speed, guess who gets to make up for it, the drive shaft. And if the center diff is locked, we have wind up.
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Old 31st August 2009, 12:11   #71
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Quote:
Originally Posted by Sawyer View Post
And when I do give the 4HL and the 4L modes a work out on tarmac, it is an untrafficked road very close to home. And in 4HL mode, I don't touch the steering wheel, and I don't get out of first. Ditto for 4L. For about 100 metres each.
IMO this is just fine for 100 metres - not for 1 km though! The Pajero is built to take a little bit of this.
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The point is...clutch slip will have to be resorted to. Or the climb will not be attempted. While coming down, engine braking advantages of 4l will be foregone.
4HL or 4LL, if engaged, will wind up the transmission irrespective of whether you are in gear or not. So, when rolling down a winding hard-tarmac road in neutral, the transmission will still wind up - except, the gearbox will not be a victim of it!
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The one time I needed it but resorted to clutch slip was when I had to climb out on steep and winding narrow tarmac.
Doing it in anger, as you put it, may have been good - if you had induced wheelspin, that would have helped to release the windup. Doing the same thing slowly and gradually doesn't set off wheelspin, so windup may not get released.
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Originally Posted by Samurai
SS-Traveller, I am no guru, but I did know the answer to my question.
I hope my answer matched yours... And oh yes, I do consider you one of the 4x4 gurus on this forum!

Last edited by SS-Traveller : 31st August 2009 at 12:20.
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Old 31st August 2009, 12:18   #72
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Originally Posted by GRV View Post
3. When I engage GV in 4L Mode does this also lock the center
differential?. I ask this because some time one need higher torque on
perfect tarmac. Due to Torque requiremet I may like to engage Low
range gear, but if I do that my drive train will be damaged (as I am on
tarmac and engaging 4L Lock means locking the center differential also)

Regards
GRV
One of the questions that led to the latest debate is again quoted above. My answer to the question still remains that if the route can be negotiated with zero steering input, using the 4l mode is fine. Given that it will be a steep climb or descent, and given that no steering input can be given, it also goes without saying that the car will be moving very slowly, even though the tarmac is perfect. If the car cannot be allowed to hold its straight line, and is on perfect tarmac, you can't use 4l, or 4HL.
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Old 31st August 2009, 12:21   #73
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Originally Posted by SS-Traveller View Post
IMO this is just fine for 100 metres - not for 1 km though! The Pajero is built to take a little bit of this.

4HL or 4LL, if engaged, will wind up the transmission irrespective of whether you are in gear or not. So, when rolling down a winding hard-tarmac road in neutral, the transmission will still wind up - except, the gearbox will not be a victim of it!

Doing it in anger, as you put it, may have been good - if you had induced wheelspin, that would have helped to release the windup. Doing the same thing slowly and gradually doesn't set off wheelspin, so windup may not get released.
Doing it in anger was a colloquialism for doing it in the real world, sorry. I am not sure where the being in neutral message came from, did not mean to convey that either.
And to clarify - because I was on a steep winding tarmac road, that was also narrow, I could not use 4l. Knowing it will wind up the drive line. I had to stay in high range, center diff open, and slip the clutch in first to prevent from stalling at the low road speed dictated by the road. That was when I realized that what is missing on the Pajero is 4l, with center diff open. Or even 2l would have worked better that day!

Last edited by Sawyer : 31st August 2009 at 12:39.
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Old 31st August 2009, 12:33   #74
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Quote:
Originally Posted by SS-Traveller View Post
...when rolling down a winding hard-tarmac road in neutral, the transmission will still wind up
Quote:
Originally Posted by Sawyer View Post
I am not sure where the being in neutral message came from, did not mean to convey that either.
The being in neutral bit was to convey the message that slipping the clutch has nothing to do with releasing transmission windup. Windup will happen when coasting too if any of the diffs are locked.
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Old 31st August 2009, 12:53   #75
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Quote:
Originally Posted by SS-Traveller View Post
The being in neutral bit was to convey the message that slipping the clutch has nothing to do with releasing transmission windup. Windup will happen when coasting too if any of the diffs are locked.
I edited my post after you wrote yours in response - the last added para is self explanatory, I hope.
Many of the soft road SUVs also come with a lock mode, without having serious 4wd gear such as low range. Cars such as the Tucson and the X trail - the Captiva too, I suspect. The Tucson, I remember had the kind of 4wd the CRV had, but it has a lock mode via a knob. Assuming using that mode has the same wind up potential, and the general lack of knowledge of this subject by the sales people who sell the car - even the people who write the brocuhres if you see the Fortuner's - I am surprised how those cars cope with an inappropriate use of 4hl. The CRV looks silly spinning its wheels like crazy, but for sure will not end up with a wound up transmission in the hands of an uneducated user. How do the other cars cope?
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