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-   -   4WD behaviour (http://www.jeepgarage.org/f109/4wd-behaviour-69649.html)

lt4vette 12-27-2013 05:26 PM

4WD behaviour
 
I have a 2014 Diesel Overland, and for the first time since I got it, need the 4WD on a steep grass slope. Unlike other 4WD vehicles I have (Landcruiser and Mazda), the Jeep seems to allow a fair bit of wheel spin before the system locks up to give the traction. maybe 1/2 to a full turn of the slipping wheel, then a loud clunk as it locks up, followed by the car jumping forward as it achieves traction. It seems to me that in difficult terrain, this would make smooth slow crawling up a hill wouldn't be possible. It happens in both Hi and Low ranges. I have only tried it in :auto: 4wd mode.
I'd like to know if may my Jeep has a problem, or is this just "normal" operation.
Thanks, Russell

SNUKE 12-27-2013 06:07 PM

Re: 4WD behaviour
 
I have had the same in my Limited - 18" with Michelin Altitudes.
Although not that steep, I don't recall it locking it up, just spinning (rear) until I removed throttle input.
I tried it ICE & MUD setting incase the wet grass was like that, no difference.
Low range was a little better, but it is no even remotely steep enough to consider low range, and it still spun eventually.
Turning of Hill Assist also helped a little as it let the car move earlier in the rev range, but still spun.

This never happened in my 2005 Mitsubishi Pajero (Montero for US readers, Shogun for UK), which didn't have the electronic wizardry considered standard these days.

I thought it just must be the tyres, but even my RWD Ford Falcon sedan doesn't do it on the same section. It weighs 750kg less, with narrower even more street treaded tyres.

I though the system would detect the wheel spin far quicker than it does and stop it.

jakibe 12-27-2013 06:12 PM

Which 4wd system do you have?

SNUKE 12-27-2013 08:16 PM

Re: 4WD behaviour
 
My Limited is Quadra-Trac II, lt4vettes Overland is Quadra-Drive II.

f1anatic 12-27-2013 08:52 PM

Re: 4WD behaviour
 
I always thought this 1/2 to full turn wheel slipping is normal behavior associated with correctly working EDL (Electronic differential Lock) with or without the assist of the E-LSD on the back. When the clunk occurs, the brake system clamps the spinning wheel, transferring torque to the opposite wheel on the same axle and thus ensuring forward motion. The brake(s) only slow down the faster spinning wheel enough to match the rotational speed of the opposite wheel.

The other cars mentioned here either have locking differentials or mechanical LSDs and there will be no clunks. I have also experienced it in my 2014 Limited with ORA II 3.6 V6 QT-2 as well in both High and Low range.

WK2OverlandII 12-27-2013 09:05 PM

Re: 4WD behaviour
 
Quote:

Originally Posted by lt4vette (Post 950858)
I have a 2014 Diesel Overland, and for the first time since I got it, need the 4WD on a steep grass slope. Unlike other 4WD vehicles I have (Landcruiser and Mazda), the Jeep seems to allow a fair bit of wheel spin before the system locks up to give the traction. maybe 1/2 to a full turn of the slipping wheel, then a loud clunk as it locks up, followed by the car jumping forward as it achieves traction. It seems to me that in difficult terrain, this would make smooth slow crawling up a hill wouldn't be possible. It happens in both Hi and Low ranges. I have only tried it in :auto: 4wd mode.
I'd like to know if may my Jeep has a problem, or is this just "normal" operation.
Thanks, Russell

I know I had a problem with my 2011 Overland Hemi with the wheels slipping too much and there were many complaints from me and others. Jeep came out with a TSB reflash of the computer and it corrected it. I loved the fix as there was very little or no wheel spin when it kicked in after the reflash...it was awesome...it was like a totally different vehicle. Maybe ask your dealer to see if there is a TSB on it or if there have been other complaints.

jakibe 12-27-2013 11:11 PM

If you look up videos of quadradrive 2 jeeps on YouTube you will see that the behavior you described is how it is designed to work. The thunk may be because the revs are too high??

lt4vette 12-28-2013 12:03 AM

Re: 4WD behaviour
 
Thanks for all the responses.
Based on them, I'd make a couple of observations:
Snuke, you don't say whether you EVER got traction from the rear - did it lock up when you removed throttle input? The different behaviour between yours and mine (mine locking up) might be due to the ELSD diff with QDII.
I agree with f1anatic that the wheel spin seems to be normal (as per the videos jakibe mentions), but I do find it surprising.
Does anyone know how other electronically controlled 4WD's (Discovery. RangeRover for example) behave?
If they are all the same, then I'd have to say that electronic control is a retrograde step. My Landcruiser with mechanically lockable centre, front, and rear diffs as f1anatic says, does not behave similarly.
It is very interesting that WK2overlandII had the issues resolved with a fix - and quite worrying if it wasn't carried through to later models - certainly worth a check though.
A couple of things which may be related:
1. I first noticed it when trying to reverse an (empty) box trailer up a grassy slope. A wheel spun, clunked as described, but we went nowhere - engine revving and stationary. Selecting Low range fixed that issue, but weird - low range would not have been required in my other (mechanical) 4WD's. What would I have done if this had been on a hard surface? (I think I have seen another post on this issue actually).
2. Throttle lag from very low speed: If I'm crawling along (almost no throttle) coming to say an intersection) and decide I have time to get across if I accelerate briskly, I get no response for 1/2 to 1 sec, then wham - ejected across the intersection. I've learnt to control this by feeding in a small amount of throttle, waiting until the car catches up to the throttle position, then accelerating. Gave my wife a fright the first time she drove it though. Does anyone else have this problem? Maybe a diesel issue as it is likely turbo lag.
I think the throttle lag problem may be a problem in the clunk and jerk action of the 4wd - quite possibly by the time the wheel locked, the revs were too high, and .as jakibe suggests, that caused the clunk - or at least made it more severe. I'll try it again more gently.
But to the most important part: I haven't tried any "serious" 4wd'ing yet, and am concerned that the delay to locking or engaging wheels, combined with throttle lag, would make it very difficult to crawl up a steep rock strewn track - has anyone tried this?

Thanks, Russell

ColdCase 12-28-2013 04:15 PM

Re: 4WD behaviour
 
I think you are seeing transmission issues, especially the lag. QD would have no influence on that behavior.

I've not had the same experience with my 2011 QD V8 and the older 5 speed transmission. I rarely get rear wheel spin, never have a bang... perhaps an occasional thump. I think you have more going on with the transmission, or perhaps transfer case.

Equipped with ELSD, when you apply throttle quickly the traction control computer will immediately lock or near lock the rear, no need for wheel spin. Mechanical systems must have wheel spin to work (unless externally mechanically locked in which case you have no diff function). In snow and perhaps rock mode the rear diff is near locked automatically. You shouldn't hear any banging unless perhaps you caught it in an awkward position with one wheel suddenly having zero traction.

You will get a banging type noise from the front BTC. If the fronts are spinning at a different rate than the rear, the throttle is pulled back.

crabman 12-29-2013 01:04 PM

Re: 4WD behaviour
 
I find the vehicle is smoother from a stop with eco turned off. It isn't just the trans shift points but also the throttle map that is altered in eco and I think it ends up being a bad combo. You get the eco trying to use less fuel until your commanded throttle input reaches a set point where it has been programmed to decide you want to move out smartly and then it ups the ante significantly to give it to you. Combined with a turbo diesel that is highly dependent on boost for power and you get a turbo that is just spooling up combined with a sudden large increase in fueling and bang, there is your surge. With eco off it acts like other diesels I've had where there is still a slight hesitation that you get around by giving it a little throttle to get rpm (and boost) up followed with a more substantial jab on the loud pedal which then moves you out smoothly but quickly. After a time you do this without even thinking about it and don't even notice it. Ive gone to switching out of eco as soon as the vehicle is slightly warmed up and I stay out of it till I'm on more open roads.

f1anatic 12-29-2013 04:03 PM

Re: 4WD behaviour
 
Quote:

Originally Posted by lt4vette (Post 951018)
Thanks for all the responses.


I agree with f1anatic that the wheel spin seems to be normal (as per the videos jakibe mentions), but I do find it surprising.
Does anyone know how other electronically controlled 4WD's (Discovery. RangeRover for example) behave?

If they are all the same, then I'd have to say that electronic control is a retrograde step. My Landcruiser with mechanically lockable centre, front, and rear diffs as f1anatic says, does not behave similarly.

Thanks, Russell

Take a look at this video, with emphasis on the Quadra Trac II equipped WK2.
Jeep QD2 QT2 - YouTube


When I first purchased the Jeep, I was expecting the Jeep's 4WD system to work more like this (mechanical limited slip differentials) but actually it doesn't. It is the ABS involvement that creates this jerky behavior of crawl forward - brake the spinning wheel(s)- torque transfer along the same axle - crawl forward and ...repeat...

And if you look at this video, you will see that even Quadra Drive 2 equipped vehicles (rear E-LSD) suffer from the same "hopping" behavior when it comes to navigating over obstacles.

lt4vette 12-29-2013 05:00 PM

Re: 4WD behaviour
 
Quote:

Originally Posted by crabman (Post 951667)
I find the vehicle is smoother from a stop with eco turned off. It isn't just the trans shift points but also the throttle map that is altered in eco and I think it ends up being a bad combo. You get the eco trying to use less fuel until your commanded throttle input reaches a set point where it has been programmed to decide you want to move out smartly and then it ups the ante significantly to give it to you. Combined with a turbo diesel that is highly dependent on boost for power and you get a turbo that is just spooling up combined with a sudden large increase in fueling and bang, there is your surge. With eco off it acts like other diesels I've had where there is still a slight hesitation that you get around by giving it a little throttle to get rpm (and boost) up followed with a more substantial jab on the loud pedal which then moves you out smoothly but quickly. After a time you do this without even thinking about it and don't even notice it. Ive gone to switching out of eco as soon as the vehicle is slightly warmed up and I stay out of it till I'm on more open roads.

I'll try it with Eco off - thanks Crabman. I did do a bit more careful observation (eco ON) and noted that it is at 1800 - 2000 rpm that the surge starts, so I'll compare this with eco off.


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