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Old 31st August 2009, 23:55   #76
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Originally Posted by Sawyer View Post
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.
Imagine your left tyre to be half inflated, while the right tyre is fully inflated. That means your left wheel is turning lot less than the right wheel. Now imagine you are driving straight in this fashion on a perfectly smooth and straight road.

If you let go the steering, what do you think will happen?

According to your logic, the steering should turn right to compensate for the under-rotation of left wheel. What happens in reality is the exact opposite, it turns left, thereby aggravating the problem.

In other words, steering wheel doesn't self correct the imbalance caused by uneven wheel rotation.
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Old 1st September 2009, 06:26   #77
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Originally Posted by Samurai View Post
Imagine your left tyre to be half inflated, while the right tyre is fully inflated. That means your left wheel is turning lot less than the right wheel. Now imagine you are driving straight in this fashion on a perfectly smooth and straight road.

If you let go the steering, what do you think will happen?

According to your logic, the steering should turn right to compensate for the under-rotation of left wheel. What happens in reality is the exact opposite, it turns left, thereby aggravating the problem.

In other words, steering wheel doesn't self correct the imbalance caused by uneven wheel rotation.
I see your point. My argument contains the assumption that all 4 wheels are of the same diameter, so that there is not an inherent imbalance in the set up. Which is how it would be most of the time for all practical purposes.
And I am also not proposing that the steering action will compensate for left/right wheel on the same axle issues. Steering action - or inaction to be precise - will however keep the car going in a straight line - in a correctly designed and maintained car, again, this is the assumption in place. Because one could also argue that because the alignment is out of whack, the car will not move in a straight line without steering input and cause wind up to happen if low range is engaged.
And it is this that takes me to still recommend use of low range on steep straight climbs/descents regardless of what the surface is like. If the car has wheels of different diameters at four corners, lots of other issues will surface long before this kind of use adds to those, also because it will be driven in that mode of 4 different dia wheels over much longer distances and times that I have been talking about.

Last edited by Sawyer : 1st September 2009 at 06:28.
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Old 1st September 2009, 08:24   #78
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Originally Posted by Sawyer View Post
I see your point. My argument contains the assumption that all 4 wheels are of the same diameter, so that there is not an inherent imbalance in the set up. Which is how it would be most of the time for all practical purposes.
In reality, there is absolutely no way to ensure all 4 tyres have same diameter. There will be millimeter or fraction millimeter differences between tyres due to wear and tear and amount of inflation. These millimeter differences can add up quickly when the tyres rotate hundred times or thousand times. For example GV tyres will rotate 448 times in one KM. Just 1mm difference in diameter can result in 3.14mm difference over one rotation. That is 14cm of difference in 100 meters, 1.4m difference in 1KM. Open differential doesn't allow any slip, it is a pure mathematical device. Therefore, the front open diff will transmit this difference back to the front drive shaft in a hard tarmac situation. In case of open or locked or no center diff, this difference will be transmitted to the transmission and rear drive shaft. This is why full time 4WD vehicles need a center diff which allows slip or center LSD. A center differential that allows slip will absorb the difference and keeps everybody happy.

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If the car has wheels of different diameters at four corners, lots of other issues will surface long before this kind of use adds to those, also because it will be driven in that mode of 4 different dia wheels over much longer distances and times that I have been talking about.
There will be always minor differences, but that gets compensated by center LSD. When you lock the center diff, then it is up to the terrain to provide the slip.
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Old 2nd September 2009, 13:50   #79
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Hi

It is very clear that driving on surface with good traction with diff lock can cause serious damage very quickly (may be just a Km is enough).

Samurai has mentioned that wet grass, gravel, sand , slush are surfaces where diff lock can be engaged without worry.

I just wonder if there is any other way one can sense / feel / find out while driving and without looking at the road surface below if wheels are slipping or not slipping before deciding to engage the diff lock.

Thanks

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Old 2nd September 2009, 16:07   #80
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@GRV, oh yes you can actually feel the rear end moving around. Until that happens, I never attempt the locked position, and in the Paj, it takes some doing to move the stick to there. For the GV, it should be a lot easier, and since you can do it in motion, you can always wait till you feel the car slipping around on the road and do it without losing way. I have found that until that time, 4H works just as well. And I guess therein lies the advantage of the center diff, you can drive in 4wd all the time if you wish, and get most of its advantages without worrying about transmission damage. Having a 2wd mode in addition confers the additional benefit of better FE and slightly less noise.

Last edited by Sawyer : 2nd September 2009 at 16:15.
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Old 2nd September 2009, 18:18   #81
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One way of making use of the huge amount of torque 4L offers on tarmac is if you have manual-locking front hubs. If you leave the front hubs unlocked and shift into 4L, what you will essentially get is 2-wheel drive, low ratio.

That would help immensely in such situations! We've used this trick years ago to get up a very steep tarmac road with a 1-litre, 45 bhp, fully-loaded gypsy (old MG410, which had manual locking hubs).

No transmission wind-up, as the front drive shafts are free to move inside the hub, but all the advantage of 2-pt-something-more-times torque going to the rear wheels. You can hear clatter in the front hubs though, but no harm done.

Sawyer - want to consider manual free-wheeling hubs as an add-on? Would greatly help. I've often wondered if it's possible to swap my auto-locking hubs on the Scorpio to manual for precisely such situations (and towing on tarmac).

Cheers,
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Old 2nd September 2009, 19:18   #82
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Originally Posted by Sawyer View Post
And I guess therein lies the advantage of the center diff, you can drive in 4wd all the time if you wish, and get most of its advantages without worrying about transmission damage.
You better qualify it as center LSD.
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Old 2nd September 2009, 19:28   #83
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@Samurai - getting to be tripping out on LSD now!
@Roshun - I see the point, but I am not sure I can install those very easily on a Pajero - or so I think. Lot easier to do this on a Gypsy I guess. How would you go about getting them for a Scorpio?
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Old 20th September 2009, 09:03   #84
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Quote:
Originally Posted by Roshun View Post
One way of making use of the huge amount of torque 4L offers on tarmac is if you have manual-locking front hubs. If you leave the front hubs unlocked and shift into 4L, what you will essentially get is 2-wheel drive, low ratio.

That would help immensely in such situations! We've used this trick years ago to get up a very steep tarmac road with a 1-litre, 45 bhp, fully-loaded gypsy (old MG410, which had manual locking hubs).

No transmission wind-up, as the front drive shafts are free to move inside the hub, but all the advantage of 2-pt-something-more-times torque going to the rear wheels. You can hear clatter in the front hubs though, but no harm done.

Sawyer - want to consider manual free-wheeling hubs as an add-on? Would greatly help. I've often wondered if it's possible to swap my auto-locking hubs on the Scorpio to manual for precisely such situations (and towing on tarmac).

Cheers,
In a current model Gypsy, if these hubs were to be installed, and used all the time in locked mode, would this be the equivalent in all respects of how the OE hub equipped car would work? Allowing for 4wd to be selected on the fly as one can just now?
If so, does this also then mean that unlocking them would allow for the use of the low range on tarmac without transmission wind up? That would allow for steep gradients on tarmac to be climbed with ease.
In practice, that would mean that one gets down to unlock them only at those rare times when low range is needed on tarmac.
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Old 20th September 2009, 09:42   #85
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Quote:
Originally Posted by Sawyer View Post
In a current model Gypsy, if these hubs were to be installed, and used all the time in locked mode, would this be the equivalent in all respects of how the OE hub equipped car would work? Allowing for 4wd to be selected on the fly as one can just now?
Yes. Installing Free Wheeling hubs and keeping them locked is same as the current OE set up in the Gypsy.

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If so, does this also then mean that unlocking them would allow for the use of the low range on tarmac without transmission wind up? That would allow for steep gradients on tarmac to be climbed with ease.
In practice, that would mean that one gets down to unlock them only at those rare times when low range is needed on tarmac.
Yes, you can use this to use low ration and maintain 2WD mode provided the added rear axles can handle the added load/strain. However, in my opinion this doesn't make sense. The whole reason for having Free Wheeling hubs is to 1) Improve Mileage , 2) Ease Steering Effort, 3) Reduce wear and tear on the front drive components when 4WD is not needed.

Realistically we will mostly know when there maybe a reason to use 4WD. For example if you are planning to take a road trip of the beaten track then you can keep the hub locked. However, if you are hitting the mall and the movie, the chance of you needing to lock your hubs are very remote. I feel it doesn't make sense to install Free Wheeling Hubs and then keep them locked all the time except when you want low range in 2WD mode.
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Old 20th September 2009, 19:15   #86
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@4x4addict - I get your point - in the city there is indeed never any need to lock the hubs for 4wd, and leaving them unlocked can be the way to save on the things you have pointed out.
Where can I get these hubs from for a Gypsy, and is it an easy install?
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Old 21st September 2009, 07:22   #87
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There is a manufacturer in Bangalore that supplies OEM for Mahindra. They also used to make for Gypsy. See this thread:

http://www.team-bhp.com/forum/4x4-te...ubs-jeeps.html

You can also consider importing the ones for the Suzuki Samurai. But, I am not sure of the part number for Gypsy. Khan may know.
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Old 25th October 2009, 10:25   #88
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Default Four-wheel drive transmissions and Limited-slip differentials (LSD)

These are from the Book written by Mr. Andrew St.Pierre White, a scholar in 4x4 system

Four-wheel drive transmissions Summary

1. Part-time four-wheel drive transmissions have two differentials; one on the front axle and one on the rear axle.
2. Full-time four-wheel drive systems have three differentials. One on the front axle, one on the rear axle and one in the centre, driving the front and rear prop-shafts.
3. A differential lock on an axle prevents differential rotation between the two wheels on that axle. (Left and right).
4. A differential lock in the centre prevents differential rotation between the prop-shafts. (Front and rear)
5. It is possible to have all three differentials lockable (full-time 4wd), or two differentials lockable (part-time 4wd). This is the ultimate traction configuration.
6. Free-wheel front hubs are used to save fuel. They are fitted to parttime four-wheel drive vehicles only. They cannot be damaged by leaving them locked.

Limited-slip differentials (LSD)


A limited slip rear differential does the same and gives the same advantages as a lockable differential but, as the name suggests, the advantage is limited.

In most cases limited slip differentials are fitted on the rear axle only. This is usually advisable, for when fitted on both front and rear axles, some limited slip differentials can alter the vehicle’s handling characteristics and cause instability at speed.
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Old 25th October 2009, 14:50   #89
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She promised to get back to me in a while and after about two hours of waiting i got a callback confirming that the Fortuner in India has LSD and only center locking diff and no rear locking diff..
@Manuuj,

For a Full Time /Permanent 4x4, there must be a Centre Differential Lock that is attached to the prop-Shafts of Front and Rear. For a LSD, it is normally attached to the axles (Front or rear) and most of the time to the Real axle.

So when the lady said that toyota has LSD and centre differential lock, then it must have a centre differential lock + front/rear or both front and real axle differential lock
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Old 25th October 2009, 19:42   #90
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Originally Posted by g_prajeesh View Post
For a Full Time /Permanent 4x4, there must be a Centre Differential Lock that is attached to the prop-Shafts of Front and Rear. For a LSD, it is normally attached to the axles (Front or rear) and most of the time to the Real axle.
Ok, you are confusing multiple things here. Here are the facts:

1) A fulltime 4x4 needs a center differential with limited slip (known as LSD), so that it allows slip between front and rear axles. A fully open or fully locked differential doesn't allow any slip between the front and rear axle. Without the center LSD, you can't drive the fulltime 4x4 on tarmac without damaging the driveline.
2) The center differential lock (which eliminates slip) is only useful for slippery condition, and should be applied under such conditions where the terrain provides the slip. A locked center diff is same as not having center diff, so it becomes same as other part-time 4x4 like Jeeps.
2) The front or rear LSD will allow slip between left and right parts of the given axle. It does nothing to compensate for the difference in front and rear axle.

Quote:
Originally Posted by g_prajeesh View Post
So when the lady said that toyota has LSD and centre differential lock, then it must have a centre differential lock + front/rear or both front and real axle differential lock
A full differential lock in rear or front is a very potent feature. You can easily break the axle under wrong usage. I doubt they give it on a SUV whose 99% of the customers are unaware of 4x4 usage.

No, I am pretty sure about this. The Indian Fortuner has center diff with limited slip with locking option. The front and rear diffs are fiully open.
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