[ph03n!x]

Originally Posted by batish

New to this sir. So need some help here. Turning as in? Example: I need to ascent a steep slope which has few curves and it isn’t possible in 2WD.

Driving in this surface you've shown in the photo will not cause a wind-up.

Originally Posted by batish

TC in locked position means 4L (Thar 2020)? Asking since that is the only gear which locks rear diff.

4H and 4L - TC here is the Transfer Case, when we move from 2H to either 4H or 4L we're "locking" the transfer case to drive both front and rear axles.

Originally Posted by batish

High traction surface needs to be only tarmac? Will this dirt road be considered as high traction surface? I am assuming this as it has no gravel to allow the wheels to spin and release windup?

Any surface where all 4 wheels are getting (almost) equal traction. This is usually on tarmac, be it black topped or cement-topped surface.

Wind-up won't occur if wheels can slip a bit in relation to the other wheels, like in your pic where the "dirt" allows slippage enough to avoid a wind-up. Same goes for all "loose" surfaces

Originally Posted by batish

Is there anything in Thar AT to prevent this or notify the driver anyhow?

Only the driver to prevent it, and a 4x4 lever stuck in 4H or L to notify

Originally Posted by batish

Locked mode refers to 4L, right? What needs to be done to prevent windup?

4H and 4L. Shift to 4H or L only when off the road. In case you find yourself on a tar or cement topped road that's too steep to climb in 2H and needs 4L, drive a bit in reverse after climbing the steep part before shifting out of 4L.

Originally Posted by batish

Found this in Thar’s manual. Can reversing after disengaging 4WD help release windup?

If a wind-up occurs, then shifting out of 4x4 will be tough (lever acts like it's jammed), and driving in reverse while in 4x4 (not after disengaging) is standard practice like it's said in the manual.


EDIT:

Originally Posted by batish

..Asking since that is the only gear which locks rear diff.

Engaging 4H or L doesn't lock the diff.

The Thar has a Mechanically Locking Differential in the rear axle that locks when it detects slippage in one of the two rear wheels - this happens irrespective of whether the vehicle is in 2H, 4H or 4L.

The front axle has Brake Locking "Differential" (BLD), which applies the brakes individually on the wheel without traction (and hence spinning freely) to allow the torque to be routed to other wheels that have traction.

When we engage 4H or 4L, we are asking the vehicle to transfer equal torque to both front and rear axle. Ideally, this means the wheels get 25% torque each - but in reality, torque will find the wheel with least resistance, which means the wheel that's spinning freely will suck all torque. This is where MLD/ BLD will kick in - MLD will lock both the wheels together and help move the vehicle, BLD will brake the free-spinning wheel.

The newer 4x4 Thars (late 2022?) with no MLD in the rear axle and the 2WD Thars have only BLD, no MLD.

What I said applies for the Thar (and other vehicles that have a lever to shift to 4x4), not as much to vehicles like Fortuner/ Endeavour 4x4 (Full time AWDs) or Duster/ XUV7OO/ XUV5OO/ Tuscan (on-demand AWDs).

[dileep]

This thread is all the more relevant since the upcoming launch of the Jimny which I'm looking forward to. i am a complete 4x4 novice. It is very educative to know how the various 4x4s work and what you should NOT do, more than what you should do.

Maybe some of the experts could write about the 4x4 of the Jimny - there's a lot of material online but none of it is written in the Indian context.
Thanks

[GooseCpt]

Recently got a Fortuner 4x4 AT and went on a trip to Wayanad. The approach to the resort was a stony road with with reasonably steep climbs with turns.
There was a also steep drop some 50m in length and a 40 degree drop - straight one on concrete and followed by few a rather steep climb with tight hairpins - total length around 60meter but with 40degree climbs with hairpins between them. The last set of hairpins was concrete with mild sand cover from the vehicles gone by.

Is this surface/climb ok to be taken on 4H on a AT Fortuner:

Since I am new to a 4x4 drive and new to a heavy SUV as well (previous drive was a 2010 Ford Figo petrol), did not want to risk wheel spin and rolling backs on the climb decided to switch to 4H and the whole climb went without any drama and we reached safely to the top.

When I had re-read the owners manual realized driving on dry surface where wheel spin is not possible could harm the drive train and transmission when driven on 4H or 4L.

Wanted to take the forums opinion on if it was ok to use 4H on the below trail.
I had driven the whole stretch around a KM of the approach stone top/gravel top road on 4H and the final 100 meters on concrete at a slow 10KMPH rolling speed. The same trail had been covered by 2 wheel drive vehicles - I saw an Innova, Creta and Lord Alto parked once I reached the top. So the trail is possible in 2H alone and did the return path in 2H.
So the main question I had was - was their undue stress from the above trail on 4h which I should continue monitoring for any issues or are things are ok from the minor wheel spins from the sand on the dry concrete and the sand top which should have released any stress once reached the top parking spot which is non paved sand top.

Had taken to service center for as the vehicle had complete 950 KMs - they had checked and confirmed everything is fine.



Approach Stony Road - It had few steeps as well - Pic for surface reference.
Does these stones allow wheel slip enough to prevent windup? I had tried moving a few of them - they are relatively loose and some them come off when pulled with hands.




Steep Concrete Climb with bends with red fine sand top from Vehicles gone by:






Final non paved Climb.


Steep Drop: Climb on the way back - covered in 2H.



Thank you!

[McLaren Rulez]

Originally Posted by GooseCpt

Had taken to service center for as the vehicle had complete 950 KMs - they had checked and confirmed everything is fine.

Don't worry, your car is almost certainly completely fine and the extra wear would be insignificant at such low speeds. Depending on how loose the surface was, 4H was probably the right call, especially for that last climb.

Just don't leave it in 4H on tarmac highway drives.

[Tejas@perioimpl]

Originally Posted by GooseCpt

Wanted to take the forums opinion on if it was ok to use 4H on the below trail.
I had driven the whole stretch around a KM of the approach stone top/gravel top road on 4H and the final 100 meters on concrete at a slow 10KMPH rolling speed. The same trail had been covered by 2 wheel drive vehicles - I saw an Innova, Creta and Lord Alto parked once I reached the top. So the trail is possible in 2H alone and did the return path in 2H.

Speed doesnt matter. Slow or fast, if the drive train has to windup, it will.

Remember the three things that have to happen together for a drivetrain windup. Any two and you are ok:

1. You must be on a high traction surface (ergo no wheel slip)
2. You must be taking a turn (even a couple of degrees of turn matter)
3. You must be in 4wd (locked) mode

So the main question I had was - was their undue stress from the above trail on 4h which I should continue monitoring for any issues or are things are ok from the minor wheel spins from the sand on the dry concrete and the sand top which should have released any stress once reached the top parking spot which is non paved sand top.

If you are able to shift to 2wd, then you shouldn't be worried. It will release the windup caused.

Does these stones allow wheel slip enough to prevent windup? I had tried moving a few of them - they are relatively loose and some them come off when pulled with hands.

When in doubt and you have no choice but to engage 4wd on a high traction surface, always air up. Carry a compressor and air up many points to reduce the contact patch and make the car bouncy in the hopes that it would bounce and loose traction and let the wheel slip.