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-   -   Driving all four wheels: how is it done? (https://www.team-bhp.com/forum/4x4-technical/90454-driving-all-four-wheels-how-done-23.html)

Hi Guys,

Since Driveline Windup can happen in Off road condition, what are protective measures to reduce it?

1) Front Axle Disconnect instead of FWH

2) Divorced T-Case usually with a 1.9:1 to 2.2:1 Low Ratio.

3) 7-11% Higher Front Axle Ratio

Regards,

Arka

Arka, understand about the ratio, but, how does Divorced TC help?
What are the effects of this on a straight line competitive start?

Hi Dhanush,

A Divorced T-Case is driven by a prop-shaft, this creates a speed mismatch (T-Case is slower than the transmission), which allows the T-Case to be shifted to 4-Low at crawling speeds, below 5Kmph.

wrt to competitive straight line starts, I dont think it will be a problem, if the front is faster, since the engine weight is up front.

But, if the rear is faster (I have seen one jeep and a Gypsy with mismatched Diff-Ratios more than 11% 5.38/4.88 and 4.1/3.73), the vehicle will jerk and move forward.

Regards,

Arka

Lets start at the beginning:- what is meant by drivetrain windup, by the people who first used this term on this thread!

Regards
Sutripta

Thanks very much for the attachment. It helped clear my doubts on different drive options and introduction to different terminologies.

What is the basic difference between MLD & 4WD with a ow ratio? MLD can be fitted on rear wheels or front or both?

If only on rear wheels, what if both wheels start slipping?

I do not know much, hence asking the pros.

MLD & 4WD Low Ratio are two different things. Cannot be compared.

MLD is locking differential, and low ratio is reduction in gearing in the gearbox, for higher torque and better control.
MLD cant be fitted on wheels. It can be fitted in front axle differential and rear axle differential.
If both rear wheels have no traction, then there is no use for the MLD. For MLD to help, you need atleast one wheel with traction.
No problem. :)

A noob at 4wd driving is looking for some answers. I'll lay out the context. I frequent an orchard near Mukhteshwar and always have a 4wd Fortuner which I'm lucky to borrow.
So far I've been practicing the following:
Stop at the gate and engage 4wd High Lock Mode-move through the 1st and 2nd gear and hold the car in the third ratio till the curves. For the steep ascent after the sharp curve, i drop to 1st and give a slight accelerator pressure, for the descent I use no driver input apart from keeping the truck in 1st gear High Lock Mode till reaching the plain parking area.
I might be making the worst mistakes here and would be grateful if someone could guide me.please:

1. What happens if i engage the 4H Lock Mode to drive up a twisty road (including two hairpin curves) on a loose surface, which comprises of a loose soil and dust atop a hard packed soil base. the top layer is so loose that merely walking on it raises dust clouds.

2. To enter the orchard proper there is sharp curve and immediately begins a steep ascent-do I engage 4wd High Lock mode or simply 4H? To give the perspective of the gradient-you only see the sky while going up and do not see the descent point till your wheel actually touches it.

3. How do I deal with the descent which is equally steep?

If MLD is fitted to both front & rear wheels, then...?

And in layman terms, how does MLD benefit a 4X4 with low GB?

Thanks a lot for your answers :)

I am not an expert. Just sharing what I learned from this thread.

Consider a scenario, one wheel from both front and rear axle doesn't have traction. Power will flow to the wheels with least traction. In this scenario, one wheel from front and rear axle doesn't have traction, and those wheels only will spin and the wheels having traction won't spin. Now you have one wheel each from both front and rear axle spinning freely and you are stuck. This will happen even for a 4X4 with Open differential(regardless of whether there is a low ratio transfer case).

When you have locking differential, which MLD is, it will help both wheels in the axle to rotate at the same speed regardless of traction. The wheel having traction will now spin you out of trouble. Hence 4X4 vehicles fitted with locking differential can be handy in situations like this.

Experts, please correct me if I am wrong

Sheel, I wouldnt recommend fitting a front locker for a road use vehicle. The problem with front lockers is that, both front wheels turn at a same speed making the vehicle stubborn to turn. The Wheels will turn, but when locker is engaged, the vehicle will continue to go in whichever direction it was going.
An MLD will help any vehicle. It neednt be a 4WD with low. It prevents vehicles getting stuck because of an open differential.

Our Storme & Scorpios do not come with MLD? What about others, Pajero Sports, Fortuner & Thar, Gypsy.

How much will the cost be to fit the Eaton MLD on my Scorpio? Will it be helpful? I do not have any plans to off road purposely on my Scorpio.

Thanks :)

None of these vehicles came with an axle differential locker, AFAIK. However, the Ghurka came with it in the front and rear.

The 4WD itself will take you to some surprisingly non-motorable roads. If you don't plan to off-road, IMO, don't fit a locker.

Since MLD locks as soon as it detects differential spin of about 100rpm, won't it put undue stress when it suddenly locks. Eg, you are on a road with one side slush. You floor the pedal and then suddenly you get the lock and jerk to the wheel with traction?
Atleast with lockers, its in your control, you can gradually increase power to avoid jerks and such.

With any lockers you don't really floor the pedal.
And, thats when the axle star breaks. :)