[Samurai]

But windup is not torque. Windup is actually stored energy. Remember the old windup watches?

This windup is created by uneven turning of front and rear shafts. And it is local to the front and rear prop shafts, and TC drive chain. Since it is local, this windup cannot be transmitted back to the gearbox.

[DirtyDan]

Originally Posted by Samurai

But windup is not torque. Windup is actually stored energy. Remember the old windup watches?

This windup is created by uneven turning of front and rear shafts. And it is local to the front and rear prop shafts, and TC drive chain. Since it is local, this windup cannot be transmitted back to the gearbox.

Well, you have restated the problem in an interesting way.

But, do the two props really turn at different speeds or is the chain binding them so robust that they cannot in which case the windup, in any form (energy?) may go where? Up the transmission output shaft?

If the chains were not robust I would expect them to break rather quickly. But they don't.

I dunno. I confess. But I am still unconvinced. And what is true of Landrover may not be true of Mahindra, may not be true of x.

Transmission windup may be a great ole myth. It was all over the forums 15-20 years ago. I just don't know at this point.

I'd like to hear from the hands on testers, B.D. or/and Spike Arrestor.

[Samurai]

Here is another take, I thought of it after I mentioned windup as a stored energy. To make use of any stored energy (say battery), the energy source has to be part of the circuit. Whether it is electrical circuit or mechanical circuit.

In this case, windup energy is part of the mechanical circuit that has prop shafts, differentials, drive shafts, wheels, tyres and the ground between the tyres. One of these has to absorb/release the windup, nothing else can. On the offroad terrain, it is the low traction between tyre and ground that releases the windup. The gearbox is not part of this circuit, so windup energy can't go there.

[Sutripta]

Some people have been chastising me for not being too economical with words. So here goes - a long post.

There are actually two issues here a) transmission wind up and its causes, and b) the effects of this windup seen by different parts of the vehicle.

The windup part has been effectively explained by lots of people here. Won't go into it again, but would like to highlight one point, that the main gearbox does not see the forces generated by this windup. Think of it this way: suppose the input shaft of the gearbox was free, and you could turn it by hand. Wind up the transmission as much as you want. The input shaft would still be free. In fact, if initially there was a fit of freeplay, it would still be there. (And which is why a TC, or releasing the clutch will not release axle windup even an iota)

What are the effects of the windup?
First of all, those forces are carried by the prop shafts/ UJs, half shafts, hubs, and that part of the transfer case which links the two axles together. Normally the UJs are the weakest link. Next would be (from personal observation) all the fancy hubs (ie freewheeling and autolocking).
Steering starts behaving funny. Not the subject of this discussion.
Most important now for this discussion - vehicle starts running heavy. The reason is that at least one axle/ tyre has to scrub or slip (if necessary, this can be discussed later), if movement has to be maintained. This extra force (torque) has to come from the engine, transmitted through the gearbox. But obviously this extra torque cannot be more than what the engine produces. (If more torque is needed, the engine will stall). And gearboxes are meant to happily handle the torque of the engine.

So this (and not the axle windup forces, which can be large) is the extra force the gearbox should see because of axle windup. And in a properly designed vehicle, should not cause gearbox failure.

Phew!

Regards
Sutripta

[DirtyDan]

I asked an automotive engineer who has decades of experience in the production and testing of 4x4 vehicles the following question. He is well known internationally, and well known in India.

If you have a prolonged windup situation on a typical part time 4x4 vehicle (e.g. driving on pavement in 4x4 mode), what would you expect the damage to be?

His time is precious so I had to keep it short and sweet with no chance for follow ups. He did not want me to give his name. Below is his answer verbatim pasted in by me.


DRIVELINE WINDUP: the first thing to go will be the hypoid axle pinion bearing preload because this is a frictionally achieved specification. Then the transmission mounting rubber pad [if any] will deform to one side. Then the synchronizers of the transmission will misbehave. Then the needle bearings of the propeller shaft will go.

Not one bit of this whole discussion will help me get chicks. But make of his comments what you will.

[Sutripta]

^^^
Except for the synchronisers, in line with what we are saying.
Would really like to know how synchronisres will be damaged.
Even better if he can point out our misconceptions/ follies/ attempts to misinform/ outright lies.

Make of our statements what you will!

Regards
Sutripta

[sudev]

Agree with Professori.
Why would synchros wear?? AFAIK these come in to play only when changing gears.

[ex670c]

Hi Guys,

Transmission Windup will happen to any vehicle with a Part-Time 4WD.

That is exactly the reason Center Differential (Locks) were invented.

Transmission windup is caused by lack of differential action between the front and Rear Wheels, this is further aggravated by the use of LSD/Lockers/Diff-Locks.

Wrt to Mahindra JEEPs and Maruti Gypsy.

The most obvious signs are
1) you will not be able to disengage the FWH,
2) shift to 2H,
3) Selecting gears will be notchy.

Transmission Windups will happen to any 4WD even in off road conditions.

This depends on design and maintenance.

The simple solution is to Disengage Diff-Locks, and drive to and fro in a straight line.

Regards,

Arka

[mallumowgli]

Originally Posted by sudev

Agree with Professori.
Why would synchros wear?? AFAIK these come in to play only when changing gears.

If I may butt in...

4WD mode is not required for the synchros to wear off. If you try to rotate the wheels in a direction opposite to the engine rotation in 2WD itself would fry the synchros. So, does a 4WD with TC locked up mode induce this condition? If so, wouldn't an auto clutch reduce the chance?

[m_upreti]

Originally Posted by ex670c

Transmission Windup will happen to any vehicle with a Part-Time 4WD.

This site as some interesting discussion on this topic

http://forum.difflock.com/viewtopic....2b07bff137a672

[DirtyDan]

Originally Posted by Sutripta

^^^
Except for the synchronisers, in line with what we are saying.

Inline except for the details and who can be bothered with those?

Originally Posted by Sutripta

Even better if he can point out our misconceptions/ follies/ attempts to misinform/ outright lies.

This engineer only commented on the effects of windup. He wishes to remain anonymous. Apparently in the past when he gave contact info he was deluged with resumes, crackpot theories, threats and all manner of nonsense from sundry malcontents, unemployed PHDs, trolls and other anti-social types with an ax to grind.

Originally Posted by mallumowgli

If I may butt in...

4WD mode is not required for the synchros to wear off. If you try to rotate the wheels in a direction opposite to the engine rotation in 2WD itself would fry the synchros. So, does a 4WD with TC locked up mode induce this condition? If so, wouldn't an auto clutch reduce the chance?

Windup constitutes increased load. The wheels, axles, don't want to rotate. Hence the transmission is stressed.

[sudev]

Originally Posted by mallumowgli

If I may butt in...

4WD mode is not required for the synchros to wear off. If you try to rotate the wheels in a direction opposite to the engine rotation in 2WD itself would fry the synchros. So, does a 4WD with TC locked up mode induce this condition? If so, wouldn't an auto clutch reduce the chance?

May be I am slow but cannot understand your point.

AFAIK synchros function when two gears rotating at different speed approach prior to slotting with each other. Once gears are slotted (engaged with each other) there is no load on synchro rings. If you do manage to stress transmission in any mode some thing has to give up in the train of mechanical lock - gears?

But may be I am wrong.

[Sutripta]

Originally Posted by DirtyDan

Inline except for the details and who can be bothered with those,

And pray, which of these 'details' is is at cross purposes to our thinking?

BTW, where do you now stand on the question which got this particular ball rolling, namely that a torque converter minimises/ prevents axle windup?

Regards
Sutripta

[DirtyDan]

Originally Posted by Sutripta

BTW, where do you now stand on the question which got this particular ball rolling, namely that a torque converter minimises/ prevents axle windup?

I did not say "minimizes/prevents' axle windup. I don't remember anybody else saying this either.

[Samurai]

DD, you said the following:

Originally Posted by DirtyDan

Auto transmissions also give some degree of protection from drivetrain "windup" in 4x4 vehicles

Let's keep our focus on this. How does your anonymous expert or you support this?