[DirtyDan]

Originally Posted by dhanushs

Sorry, I dont have much experience driving automatics, but, isnt the drivetrain wind up caused because the "transfer case" is locked, and not the gearbox?

The transfer case doesnt allow different speeds of front and rear prop shafts. and, when they try to do the same the drive train winds up?

Well, depressing the main gearbox clutch doesnt lessen the wind up. Releasing the front prop shaft drive does.

Oh? If you detach the fly wheel and engine from the wind up, you eliminate a big chunk of what the windup is winding up against, do you not?

Damage from windup is often to the transmission first off, then maybe the prop universal joints, the clutch. Maybe the T-case somewhere in the scheme of things. The fact that damage very often occurs elsewhere in the drivetrain, other than the T-case, tends to throw doubt on dhanushs' idea. Does it not? ANd of course, no one ever questioned that taking away the front axle was NOT going to impact windup. That's absurd.

And, does disengaging the clutch LESSEN (not eliminate) windup? Correlatively, do automatic transmissions fare better (somewhat) with windup due to inherent slippage?

Note from Mod : Please DO NOT be rude and use abusive language. If this is repeated, you will be infracted

[dhanushs]

Originally Posted by DirtyDan

Oh? If you detach the fly wheel and engine from the wind up, you eliminate a big chunk of what the windup is winding up against, do you not?

No.

Where does the windup occurs? And due to what reason?

DD, I guess you own a manual transmission, manual steering 4x4 invader with low ratio?

Do you agree that when driving on hard grippy tarmac, with 4x4 (H or L) engaged and FWH locked, there occurs drivetrain windup? And the symptom on this can be seen in your steering? It pushes towards the opposite side on full lock turns?

If so, can you please explain what will happen (to the steering push symptom) while going downhill, on a hard grippy tarmac, with 4x4 low engaged, you DEPRESS the clutch & take a turn? Does the steering push suddenly stop and it frees itself when you DEPRESS the clutch?

[tsk1979]

Danush is right.
The windup is on the axles. Even if you shift in neutral when in 4WD, and turn vehicle, you will see the effects. Try it yourself.

Engage 4WD (L or H does not matter)
Start rolling downhill on hard tarmac in neutral and then start turning steering.

Your gearbox (Auto or manual) does not have anything to do with it. If you have a transfer case without any center diff, it will always try to rotate front and rear wheels at same RPM, and you will get windup, gear or no gear.

[DirtyDan]

Originally Posted by tsk1979

Danush is right.
The windup is on the axles.
Your gearbox (Auto or manual) does not have anything to do with it.

Well, certainly I agree that windup is caused by the front and rear axles turning at different speeds and the front and rear props meet at the TC but the damage to the drive train is most often to the transmission in MT applications so I am not convinced at this point that the clutch and tranny do not play a roll. Please note, once again, that I never ever said that disengaging the clutch on an MT would eliminate all windup. But the bald fact that windup damage is most commonly to the tranny makes me think that clutch and tranny MUST play a roll.

You have a transmission input shaft coming from the clutch which is mechnically linked via the gears to the tranny output shaft to the TC, that is resisting turning due to windup. The resulting friction usually cooks and carbonizes the tranny gear oil and then the innards melt due to heat and lack of lubrication.

I blew up a MT tranny via windup one fine day and there were no steering symptoms whatsoever prior to the MT gears failing totally, no hint of any kind of something going amiss, until it was too late. I had to rebuild the tranny. Everything else was okay including the TC. I wish it had destroyed the TC, TCs are cheaper.

[SS-Traveller]

Remove the engine.

Remove the gearbox.

Keep the rest, with transfer case engaging both front and rear prop shafts (4H/4L, doesn't matter).

Now roll / tow the vehicle on a twisting road.

Report back what happens.

[DirtyDan]

Originally Posted by SS-Traveller

Remove the engine.

Remove the gearbox.

Keep the rest, with transfer case engaging both front and rear prop shafts (4H/4L, doesn't matter).

Now roll / tow the vehicle on a twisting road.

Report back what happens.

And just what is this test supposed to show? That there is still windup? Agreed. But that is not the point. We all agree on the proximal CAUSE of windup.

[Rahul Rao]

Only way to release windup is to shift from 4 WD to 2 WD nothing else will release it. If you get off the road into rough gravelly surface, your tires will slip and release it.
The simple fact that you are getting windup means you are using 4WD where you do not need it. In an AWD there is no windup as there is a third differential between the two axles, but even here if you use the AWD lock on a good surface you will get windup.

Rahul

[Sutripta]

Finally one understands where DD is coming from

Originally Posted by DirtyDan

I blew up a MT tranny via windup one fine day and there were no steering symptoms whatsoever prior to the MT gears failing totally, no hint of any kind of something going amiss, until it was too late. I had to rebuild the tranny. Everything else was okay including the TC. I wish it had destroyed the TC, TCs are cheaper.

though I'd say running in 4X4 was a coincidence, and not the cause.
But I'd like to know the thought process of others who share the same view as DD.

Originally Posted by DirtyDan

And just what is this test supposed to show? That there is still windup? Agreed.

That the forces generated are not transmitted through/ to the main gearbox.

Regards
Sutripta

[DirtyDan]

Originally Posted by Sutripta

That the forces generated are not transmitted through/ to the main gearbox.

Well, since the gearbox in this test is sitting on the garage floor while the rest of the vehicle is bouncing down the road, I think you are quite correct in this case.

[tsk1979]

I have a question.
Let us assume, that Auto transmission due to fluid whatever allows slippage.
What is slippage.
Slippage is front and rear diff rotating at different speeds

4x4 Manual scorpio. Front diff rear diff no center diff - The front and rear diffs have to rotate at same speed - Am I correct?
4x4 Auto Scorpio - Due to fluid whatever, front and rear diffs can rotate at different speeds. - IS THIS CORRECT?

Before you answer this question. Look at this image


In a Car what is your gearbox connected to? DO two shafts go outside to each diff?
No, they do not.

Gearbox output shaft goes to transfer case which decides whether to spin front shaft or not. When engaged, front shaft and rear shaft operate at same RPM.

This is where SLIP is needed. While turning, there should be a mechanism which allows front shaft and rear shaft rotate at different speeds.

Now how this is possible in Auto Tranny scorpio.
I can think of one way. Due to low quality, the tranny leaks oil, which goes to transfer case which allows slip

[ringoism]

Originally Posted by dhanushs

Sorry, I dont have much experience driving automatics, but, isnt the drivetrain wind up caused because the "transfer case" is locked, and not the gearbox?

The transfer case doesnt allow different speeds of front and rear prop shafts. and, when they try to do the same the drive train winds up?

Well, depressing the main gearbox clutch doesnt lessen the wind up. Releasing the front prop shaft drive does.

Absolutely right (AFAIK), unless it's a 4X4 (AWD) system like AMC Jeep's full-time "Quadratrac", which used a viscous coupling (or was it a differential with limited-slip? - Wiki that) in the transfer case between the front and rear drives, in which case windup is an impossibility. In more conventional 4x4 systems windup is not going to be lessened by having an automatic gearbox. As you say, it is an issue of different amounts of rotation between the front/rear prop shafts. The gearbox, whether manual or auto, is out of that loop, so to speak.

This thread went a long way since I saw it a few days ago, and no time to check it all out, but it's fine with me. I'm a tech guy and there wasn't much left to say IMO about the vlx anyway (except that I did NOT experience anything like windup at any time traveling at 45kmph in 5th gear / 4L up Kunzum-La's gravel track ).

-Eric

[DirtyDan]

Originally Posted by tsk1979

Gearbox output shaft goes to transfer case which decides whether to spin front shaft or not. When engaged, front shaft and rear shaft operate at same RPM.

There are at least two issues here which seem to get confused.

1.) One is that an AT or MT stands physically between the front and rear axles and can prevent windup. That obviously is not true. Despite my mis-statements previously, this is not what I meant. My fault for not being a lot more careful with my words.

2.) The another issue is where windup is located. This is not the same maybe as where does, how does it start. We all agree that the proximal cause is the front and rear axles travelling at different speeds. This is where it starts. But I would suggest to you that "windup" can be thought of as resistance (It can be thought of as other things, too). We can see from tsk1979's drawing that the chains of the TC connect the TC to the transmission. As he points out this is a hard connection, no slippage. But this is precisely which causes friction as the torque from the motor moves against the drag and friction of the windup. This, I maintain, OFTEN causes "transmission windup" and ultimately transmission damage and failure. There is probably a statistical record out there someplace of the frequency of breakage of drivetrain parts due to windup but I have been unable to find it via Google. The last thing I remember seeing is that transmission damage is first in frequency followed by TC failure second and then everything else including clutch, universals etc. But I cannot find that info and it may be out of date now anyway. It is probably vehicle and product dependent as well.

I think a lot of you are mistaking the cause of windup for the effects. That is my two rupees on the subject. I am not too inclined to pursue this further. It would be nice to hear from B.D. and Spike Arrestor on the EFFECTS of windup on the drivetrain.

[Samurai]

Originally Posted by DirtyDan

As he points out this is a hard connection, no slippage. But this is precisely which causes friction as the torque from the motor moves against the drag and friction of the windup.

Say this hard connection is removed, as in gearbox itself is removed. Does the windup vanish? In post#306 you agreed it doesn't vanish. On that we are all on the same page. If the presence or absence of gearbox doesn't eliminate the windup, why should AT gearbox change anything?

[tsk1979]

Originally Posted by DirtyDan

I think a lot of you are mistaking the cause of windup for the effects. That is my two rupees on the subject. I am not too inclined to pursue this further. It would be nice to hear from B.D. and Spike Arrestor on the EFFECTS of windup on the drivetrain.

Also consider this. Lets say transfer case is 1:1 ratio(hypothetical).

If you are turning the vehicle, with part time 4WD engaged your front wheels are forced by good traction on the ground to rotate faster than the rear
the front drive shaft tries to slow down the rear. So the stress is at the transfer case end. Gearbox is out of the picture.

Related article
http://www.4x4abc.com/4WD101/def_turnpart.html

Here is a forum discussion about the same. People agree that is the transfer case and downstream components which will be damaged, not the transmission itself
http://www.landroversonly.com/forums...mission-97297/

One reply

The only way the transmission could be damaged is if the transfer case completely self-destructs and also takes out the transmission output shaft. Pretty unlikely.

Conversely, driving too much with the CDL unlocked in loose traction surfaces can cause the center diff to fail as the centrifugal force throws the oil out of the bearings/gears.

One way you can damage gearbox is starting from standstill with wheels turned. You will stall vehicle. But if you Give throttle to overcome this and do a clutch dump then of course, it means Gearbox damage.

Is that what you are saying DirtyDan?

If you had large tires and were in a tight spot with the wheels locked on solid a surface. You may have a severely binding drive line. If you gave a good shot on the throttle, the transmission, weather automatic or manual would be really stressed, because nothing is moving. That would be like driving against a brick wall. If it was going to break that would be the time. I'm thinking the torque converter would be the first thing to go.

I think this is what you are trying to say. If so, then in this case it has nothing to do with 4WD. You can cause the same damage to vehicle by towing a really really heavy thing with your scorpio.

Lets say you fix your scorpio to a 20,000 ton earth mover or JCB. Then you try to pull. Of course you will stall. You dump clutch and spin wheels. Lets say you are on very grippy tires on a very grippy surface which does not allow slip. You dump clutch in manual tranny. Of course you can damage gearbox.

With AT, if there is viscous coupling, you won't immediately break something.
But with MT also, you can damage clutch(burn out clutch) and not break gearbox.

Infact, if a vehicle breaks gearbox instead of burning the clutch to kingdom come, this is a sign of poor design.

I think I have finally understood what you are trying to say.

[DirtyDan]

Originally Posted by Samurai

Say this hard connection is removed, as in gearbox itself is removed. Does the windup vanish? In post#306 you agreed it doesn't vanish. On that we are all on the same page. If the presence or absence of gearbox doesn't eliminate the windup, why should AT gearbox change anything?

Think of wind up as torque. If you disengage the clutch MT, or if you have a much more slippery torque converter, AT, with fluid coupling instead of a harder connection, you have detached the motor and flywheel thus eliminating some resistance, thus eliminating SOME torque friction in the tranny. Tranny windup. That is what I was thinking of. If you rolled down a steep hill in windup mode with the engine off, maybe you could visualize this easier.

TSK1979, I have not read your stuff yet. Maybe if I had, I would not have written this ridiculous garbage above.