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Old 29th May 2016, 21:36   #406
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Vikram Arya View Post
. As there is no manual intervention to engage/disengage the AWD, there is no way to disconnect the drive train from transmission completely and in such a case if the vehicle is towed with any/two wheels on the ground it will damage the transmission componentry.

Therefore AWD vehicles should only be towed on a flatbed.
I think the original question was towing with all wheels on the road, AWD powered off.

Regards
Sutripta
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Old 8th June 2016, 19:15   #407
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You could start off in 3rd gear in 4L.. Not a problem in most situations
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Old 9th June 2016, 15:56   #408
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Sheel View Post
In 4L, can we directly engage 2nd gear and or go till 3rd gear [from 1st and 2nd] w/o much/any A pedal input?

I had to encounter slush and 4H could have cleared it, but because 4L wasn't engaged for a while, I engaged 4L and gingerly tackled it in 2nd gear.
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Originally Posted by BlackPearl View Post
Yes, in most cases you should engage 2nd gear in 4 Low unless you absolutely need the highest torque available in 1st gear.
I think you should consider 4L just as reduced gearing. So, I would say, you can drive in which ever gear you want. Lower the gear, lesser the speed and more wheel control.
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Old 9th June 2016, 20:29   #409
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Default Re: Driving all four wheels: how is it done?

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Why would one want to drive in 4L in 3rd gear? What speed would be in 3rd gear at 4L? No issues with drive-train? What advantage would it have over 4H in 1st or 2nd gear?

TIA
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Old 9th June 2016, 23:09   #410
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Sheel View Post
Thanks for replies

Why would one want to drive in 4L in 3rd gear? What speed would be in 3rd gear at 4L? No issues with drive-train? What advantage would it have over 4H in 1st or 2nd gear?

TIA
Consider an obstacle, where you need to gain adequate momentum, but then towards the apex, need more climbing torque. You can start of in 3rd low, and shift to 2nd low, all the while keeping the vehicle moving. 1st high is similar to 3rd low (gear ratio) , but then you need to stop to change from high to low and then to 2nd gear. After which the vehicle might not clear the apex.

Same case with 3rd low then 4th low and then back to 2nd.
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Old 13th June 2016, 19:18   #411
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Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Sheel View Post
Thanks for replies

Why would one want to drive in 4L in 3rd gear? What speed would be in 3rd gear at 4L? No issues with drive-train? What advantage would it have over 4H in 1st or 2nd gear?

TIA
During a few OTRs that I went to, while climbing a hill from stand-still, the advice from UB Sir (of Kolkata offroaders) was to engage 3rd in 4L, rev up the engine, then release clutch to get the momentum enough to climb to the top. That almost always worked. Did that many times in my stock Scorpio 4wd. I guess engaging 3rd directly gives the momentum (having to change from 1st to 2nd to 3rd in the middle of the climb invariably makes you lose the momentum and you can't make it), and 4L gives much more torque than 4H, and the combination of above gets you through. While climbing up the Sandakphu trail, most of the times I was on 2nd in 4L (except the hairpins), and even some parts of the last 3 kms. Till now, no damage to drive-train detected.
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Old 13th June 2016, 23:52   #412
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Default Re: Driving all four wheels: how is it done?

This thread has been a revelation. Thanks to all who wrote and explained, that after 23 years of driving, I finally understand (well, kind of) what that football-like thingy found on the underside of vehicles actually does.

However, funny thing is, there is a down-side for me now after reading this thread. You see, before I read up all the details here about open and limited diffs, and Sushmita Sen's brother, and scenarios of one wheel hanging in the air and two others slipping, and the torque-genie ignoring the 4th wheel and blah, blah, blah, I never thought twice about taking my Scorpio through different kinds of roads and terrain, including loose sands of Puri and Baruva beaches, or top of the dunes at Hunder, or some really nasty patches of deep mud in Medinipur, or a snow-bound Kunzum pass. Maybe I'm lucky that I didn't get stuck even once (touch-wood) or maybe I knew my limits, or maybe even a remote possibility that I am a damn good driver . However, going forward now, I will probably be much more cautious while confronting such terrain, as Shamindra-da's opening question "driving all four wheels: how is it done?" and all 28 pages of this thread will run through my mind first. Maybe for the better.
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Old 22nd November 2016, 19:04   #413
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Question Re: Driving all four wheels: how is it done?

I have a question about the Storme shift-on-fly part time 4x4 system.

Per my understanding, 4H light on center console glows ONLY after
1. transfer case has connected the front output shaft to rear output shaft
AND
2. the front axle disjoint pieces are connected.

A move from 2H to 4H , would need front disconnected shaft's splines to be aligned, before connecting sleeve can move over the splines and join the two parts.
But how do splines align if the car is stationary? And how does the 4H light come up indicating that the second step is complete?

I have tried moving my car from 2H to 4H when stationary, and 4H light glows solid every time. How?
Is there a gap in my understanding? Something that I am missing?
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Old 23rd November 2016, 10:30   #414
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by black_rider View Post

I have tried moving my car from 2H to 4H when stationary, and 4H light glows solid every time. How?
Is there a gap in my understanding? Something that I am missing?
The 4H light comes on as soon as the TC engages the front drive shaft. When the front drive shaft is disengaged, the light goes off. That is all.
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Old 23rd November 2016, 17:44   #415
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Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Vikram Arya View Post
Therefore AWD vehicles should only be towed on a flatbed.
I have an XUV500 AWD and this is what the user manual says:

AWD vehicles have to be towed only with the rear wheels lifted off the ground
or on all four wheels. If vehicle needs to be towed by lifting the front wheels,
then the propeller shaft needs to be disconnected in order to protect the
coupling.


All this is fine if the vehicle is towed in front of us. But what if the vehicle is towed away by the cops? How does one ensure that they follow the correct procedure?
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Old 24th July 2017, 23:12   #416
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Default Re: Driving all four wheels: how is it done?

I have driven only simple 4WD vehicles, where the differentials can be locked or unlocked, or have LSD. The newer models with terrain modes sounds neat, but I don't understand what they really do.

For example, let's consider the Jeep Compass 4WD system, which has auto/sand/snow/mud modes. I have done extensive driving in snow, sand and mud, and know how to change my driving style to suit the terrain. And it is a combination of how I accelerate, brake, steer and choice of gear ratio.

However, I am unable project this into modes like sand/snow/mud. What does the 4WD system do when each of these modes are selected? And what does it do in auto?
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Old 25th July 2017, 12:06   #417
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Samurai View Post
I have driven only simple 4WD vehicles, where the differentials can be locked or unlocked, or have LSD. The newer models with terrain modes sounds neat, but I don't understand what they really do.

For example, let's consider the Jeep Compass 4WD system, which has auto/sand/snow/mud modes. I have done extensive driving in snow, sand and mud, and know how to change my driving style to suit the terrain. And it is a combination of how I accelerate, brake, steer and choice of gear ratio.

However, I am unable project this into modes like sand/snow/mud. What does the 4WD system do when each of these modes are selected? And what does it do in auto?
Both my SUVs are AWD with a viscous coupling and no low range option, however, I have rented Wranglers & Grand Cherokees a number of times to drive in treacherous conditions that included a 120 kmph blast on the Coquihalla highway in -20C with snow on the ground. Even if the vehicle had one of these systems (Grand Cherokee has a "Selec-Terrain" system) I have never felt the need to use one and have relied on my personal driving style and experience that was acquired over the years (limited to snow/ice, very rough surface, no rock crawling, very little sand or mud). Having said that I am not implying that these systems do not deliver what they promise; I have just not used one. Yes, I do have a Gypsy back home that we all know does not have any of these fancy gizmos other than a low range transfer case.

A few years ago while working on the B2C side when I was dealing with FCA, I asked a similar question to one of their technical guys and here’s the gist of what I understood/remember:

Snow/Gravel: On any hard but low traction surface such as gravel or compact snow the system changes the throttle mapping to provide a gradual response that will help prevent the wheel spin. The transmission kicks into 2nd gear at take-off that again helps reduce the wheel spin. The electronic centre/rear differential switch to higher preload setting and will come into action sooner. The traction control also switches to steeper response curve. Hill Descent Control that uses the ABS to maintain a slow speed on steep declines is automatically engaged in low range if the vehicle is equipped with one.

Mud: In this setting also the throttle mapping is altered to reduce wheel spinning however the transmission takes off in 1st gear and will stay in 1st under light throttle. The transmission will shift into a higher gear when the throttle is increased. Traction control curve is less aggressive to allow slightly more tire slippage to help generate traction.

Sand: Though in the initial stages one requires gentle throttle, however, once you have gained momentum you would want to maintain enough speed to avoid getting bogged down. In this mode, the system kicks off the throttle gradually but ramps up the response with increased velocity. In the sand mode, the transmission both upshifts & downshifts quickly to keep the engine within its power band. Traction control curve is linear.

Rock: Throttle mapping is very gradual and progressive in this mode as we all know precise throttle application is critical along with brake and steering input. Transmission kicks off in 1st gear, stays there longer and downshifts much quicker to maintain slow speeds. Both HDC & TC have a very aggressive curve to reduce speed quickly on steep declines.

As for the auto mode, I guess the system algorithm takes inputs from engine speed, throttle position, steering movement and the vehicle velocity in addition to other sensors to provide an optimum setting for various drive train systems that would best serve the terrain in question.

I must also mention that this description pertains to a generic "Terrain Response" systems and not specific to Jeep Compass/other FCA vehicles. Such systems on vehicles equipped with locking differentials, LSDs, low range option would function similarly, however, will have pronounced effect on account of these additional 4WD oriented enhancements.

Hope this helps somewhat.

Last edited by Vikram Arya : 25th July 2017 at 12:16. Reason: Addition of content
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Old 25th July 2017, 14:55   #418
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by Samurai View Post
However, I am unable project this into modes like sand/snow/mud. What does the 4WD system do when each of these modes are selected? And what does it do in auto?
Cross posting from this (Preview: Ford Endeavour) thread:
Driving all four wheels: how is it done?-tms.jpeg

Last edited by S2!!! : 25th July 2017 at 14:57.
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