[shashanka]

Originally Posted by DirtyDan

Drivetrain windup gives testimony as to just how much traction......and a good mobile with which I can call Rahoon and his intrepid M&M tractor .

Very lucid and crisp narrative, Dirty Dan - tar road, no centre diff or VC, and 4WD - the hair-raising effects of torque wind-up in these circumstances is made crystal clear in your narrative!

[shashanka]

Originally Posted by Tejas@perioimpl

So theoretically, if a car has an all wheel steering (the back wheels move in opposite direction to the front), then the wheels will move in the exact same distance and there will be no transmission wind up?

Dr. Tejas, the point you have raised is interesting. But 1) steering angle is not the same for the front and rear wheels; 2) rear wheels turn in opposite direction to the front at low speeds and : 3) they turn in the same direction at higher speeds. The steering input to the rear wheels is quite complex and depends on several variables - vehicle speed, front wheel steering angle etc. Thus the need for the centre diff/ viscous coupling remains for full-time AWD applications. But for old-fashioned 4WD systems - my BS6 Thar manages with this! - driver skill (mine in this case!) is paramount for avoiding torque wind-up issues.

[Tejas@perioimpl]

Originally Posted by shashanka

Dr. Tejas, the point you have raised is interesting. But 1) steering angle is not the same for the front and rear wheels; 2) rear wheels turn in opposite direction to the front at low speeds and : 3) they turn in the same direction at higher speeds. The steering input to the rear wheels is quite complex and depends on several variables - vehicle speed, front wheel steering angle etc. Thus the need for the centre diff/ viscous coupling remains for full-time AWD applications. But for old-fashioned 4WD systems - my BS6 Thar manages with this! - driver skill (mine in this case!) is paramount for avoiding torque wind-up issues.

You've quoted a 12 year old post!

My fundamentals are much more clear now about drive train windups.

In a nutshell, three issues have to be there together to cause a drive train windup:

1. You must be turning
2. You must be driving with TC in locked position
3. You must be on a high traction surface

Only if these three factors are there you will get a windup. Any 2 and you will not get a windup.

[shashanka]

Originally Posted by Tejas@perioimpl

You've quoted a 12 year old post!

My fundamentals are much more clear now about drive train windups.

In a nutshell, three issues have to be there together to cause a drive train windup:

1. You must be turning
2. You must be driving with TC in locked position
3. You must be on a high traction surface

Only if these three factors are there you will get a windup. Any 2 and you will not get a windup.

Thank you sir! I don't have a TC (the Thar is manual) and I shall certainly remember not to engage 4WD on tarmac.

[Tejas@perioimpl]

Originally Posted by shashanka

Thank you sir! I don't have a TC (the Thar is manual) and I shall certainly remember not to engage 4WD on tarmac.

TC - transfer case

Your thar has it.

[Tgo]

Originally Posted by Tejas@perioimpl

My fundamentals are much more clear now about drive train windups.

Is it possible to experience a windup in a Duster AWD? It has a electronic clutch pack that engages the rear differential. Its placed in in the rear diff housing as a result the prop shaft is always rotating even in 2WD mode.

I was experiencing a weird resistance while moving from standstill. Felt like at the clutch bite point the car hesitated just for a second. Similar to the way a hill hold function lets go of the brakes suddenly. I also noticed a sound which I could best associate with the prop shaft jumping (juddering, as this has a dual mass flywheel so there is some rotational damping effect there as well). Do these symptoms correlate to the windup phenomena?

I thought following the freeing up (going back and forth on full lock on loose surface) procedure did work on a few occasions but it could be psychological too.

Just want to understand my vehicle better and possibly not end up damaging the components.

[SS-Traveller]

Originally Posted by Tgo

Is it possible to experience a windup in a Duster AWD?

The prop shaft & clutch pack transmit power to the rear axle without causing a wind-up, since the clutch allows slippage between the front and rear axles (works like a differential, but controlled electronically). Due to the slippage being allowed, the clutch pack is known to overheat and wear out if subjected to extreme off-roading. Such a clutch will exist in some form for all 4wd vehicles where the primary drive is to the front wheels, and the engine is mounted transversely - hence, Duster, Compass, Yeti, XUV500 AWD all have such a slipping clutch as part of the rear prop shaft, and controlled electronically, in some form or the other. The Skoda clutch unit even has a name - Haldex.

I was experiencing a weird resistance while moving from standstill. Felt like at the clutch bite point the car hesitated just for a second.

It takes the electronics a few milliseconds to detect wind-up and release the clutch, to prevent transmission damage. You might feel that kind of resistance if you are operating in AWD locked mode.

[Tgo]

Originally Posted by SS-Traveller

The prop shaft & clutch pack transmit power to the rear axle without causing a wind-up, since the clutch allows slippage between the front and rear axles (works like a differential, but controlled electronically). Due to the slippage being allowed, the clutch pack is known to overheat and wear out if subjected to extreme off-roading. Such a clutch will exist in some form for all 4wd vehicles where the primary drive is to the front wheels, and the engine is mounted transversely - hence, Duster, Compass, Yeti, XUV500 AWD all have such a slipping clutch as part of the rear prop shaft, and controlled electronically, in some form or the other.

So only if the clutch has fused shut due to heat or is malfunctioning and staying closed all the time, will a wind-up occur. Sounds right.

Wondering what the fail position is. Logically should be fail to open.

Even after 3 years since getting my differential replaced, I am still trying to figure out what caused it to fail. I have pinned it down to one instance of real-wheels-on-the-ground towing (about 20 kms) which is not recommended for AWD cars. But still trying to understand why??

[Tejas@perioimpl]

As SS said it will not let a wind up happen.

Most newer cars will have this fail safe. The New Endy also has sensors to prevent a windup

However, if you continuously keep driving on high traction surfaces in Locked mode, there will be instances of torsional stresses on components before the system releases the windup and eventually you will damage and break some component due to this. So it is not advisable to drive in AWD mode unless you have a centre diff or a car especially build for AWD on tarmac.

[SS-Traveller]

Originally Posted by Tgo

Even after 3 years since getting my different replaced, I am still trying to figure out what caused it to fail. I have pinned it down to one instance of real-wheels-on-the-ground towing (about 20 kms) which is not recommended for AWD cars. But still trying to understand why??

That is the cause. The clutch would have remained engaged for some reason, but forced to slip because the engine / gearbox was not running at the same speed.

[SPIKE ARRESTOR]

Originally Posted by Tejas@perioimpl

Most newer cars will have this fail safe. The New Endy also has sensors to prevent a windup

Would be interesting to know how this fail safe works, do you by any chance have more details of the same? What kind of sensors are you referring to here?

Spike

[ruzbehxyz]

Originally Posted by SPIKE ARRESTOR

Would be interesting to know how this fail safe works, do you by any chance have more details of the same? What kind of sensors are you referring to here?

The 4WD Endeavour is a Full time 4WD and equipped with Terrain Management System which is an intelligent system. Every second the ECU receives data from all sensors and decides what's best for the vehicle, keeping the parameters in control. Its a fail safe mechanism unless if you engage 4L on tarmac or lock the rear differentials and take a harsh turn.

https://youtu.be/BYy4rCNpilk

[shashanka]

Originally Posted by Tejas@perioimpl

TC - transfer case

Your thar has it.

Oops! My mistake, Dr.Tejas! And thank you once again.

[Kosfactor]

Originally Posted by Tgo

Even after 3 years since getting my differential replaced, I am still trying to figure out what caused it to fail. I have pinned it down to one instance of real-wheels-on-the-ground towing (about 20 kms) which is not recommended for AWD cars. But still trying to understand why??

This should answer it.

https://en.m.wikipedia.org/wiki/Viscous_coupling_unit

Usually both sides are spinning when the vehicle is in motion but when towing with rear wheels on the ground and front wheels are locked, the output spins and the input side of the rear viscous coupling stays still causing it to heat up and does the damage afterwards.

[batish]

Originally Posted by Tejas@perioimpl

My fundamentals are much more clear now about drive train windups.

In a nutshell, three issues have to be there together to cause a drive train windup:

1. You must be turning
2. You must be driving with TC in locked position
3. You must be on a high traction surface

Only if these three factors are there you will get a windup. Any 2 and you will not get a windup.

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.

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

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?

Originally Posted by Tejas@perioimpl

As SS said it will not let a wind up happen.

Most newer cars will have this fail safe.

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

However, if you continuously keep driving on high traction surfaces in Locked mode, there will be instances of torsional stresses on components before the system releases the windup and eventually you will damage and break some component due to this.

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

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