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post #41 of 48 (permalink) Old 03-15-2017, 04:30 PM
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I know how a wet clutch works. As the discs spin faster, this generates heat, which thickens the lubricant (goo!) and pushes all the discs together. So, even when these discs are locked together because of the heat from the lubricant, this still allows for slippage between the front and rear axles. In 4LOW, the drive lines are locked together, so there must be some electronic algorithm that locks the clutch discs, which overrides their normal operation. I'm new to the forum and new to this drive train, so all of this is probably a rehash to those who have been here for the past 3 years. I've been walking around the kitchen for the last hour trying to figure out how this works! My head is going to explode.

According to my 784 page Owner's Manual, driving in 4LOW on dry, hard surfaces may cause increased tire wear and damage to driveline components. Thus, there is NO allowance for slippage between the front and rear axles! This is your dead giveaway!

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post #42 of 48 (permalink) Old 03-15-2017, 04:58 PM
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Except mine showed the 4wd temp unavailable last time after half hour in 4 low which led me to think maybe it does still allow for some slip. I have tried and tried to get the answer from Jeep but they either don't know, don't care or won't share. In think a little of all three.

I sent them 3 emails over the past 6 months and no reply to any (looking for Navigation fixed promised over a year ago). Mentioned this on the FB page (FCA Aus) and got a private message in minutes apologising and asking for my details so Customer Care could contact me. Great! That was 6 days ago. Not a word...

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Cheers, Dave.


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post #43 of 48 (permalink) Old 03-15-2017, 05:59 PM
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.... I have tried and tried to get the answer from Jeep but they either don't know, don't care or won't share. In think a little of all three.
Wonder if American Axle would respond. It's their system. However, there may be an agreement between companies about not spilling more beans than agreed to in contract???
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post #44 of 48 (permalink) Old 03-15-2017, 06:22 PM
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.... I've been walking around the kitchen for the last hour trying to figure out how this works! My head is going to explode.
Haha! There was a thread back in 2014 where this drivetrain was discussed and a few heads probably exploded then too.

Figure out how it can switch between a torque bias of 60/40 to 40/60 and then up to 100% torque to the rear wheels when the front differential is always gear connected to the transmission (except in Neutral Mode, but that's just for towing behind another vehicle). Then throw in things like yaw control, lateral movement detection, vehicle center of mass, reacted rear wheels, torque versus power, more effective during spirited and off-road driving. It's all and engineering quagmire. I posted a thread that dealt with some of this: Torque Split Uncovered. It's not your father's Oldsmobile. I am not an engineer, but what I've read indicates the ability of the wet clutch to be slipped and pulsed is a factor. This has always led me to believe that, for longevity sake, the TTD is only closed when needed. And if driving conditions push it beyond its design limits, it will bow out until it can recover.

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post #45 of 48 (permalink) Old 03-15-2017, 06:53 PM
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When I was a kid, I always wanted to see how things work. I'd take things apart, but I always had to get them back together before my Dad got home from work! For the most part, this worked. On the occasions where I could not get whatever it was back together before the allotted time, my bare butt paid the price! To this day, curiosity still gets the better of me.

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post #46 of 48 (permalink) Old 03-15-2017, 07:14 PM
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When I was a kid, I always wanted to see how things work. I'd take things apart, but I always had to get them back together before my Dad got home from work!
Me too. Just not smart enough to ever get them back together. Well, I did get his '54 Plymouth station wagon running again.

I asked John D. Kelly at Weber State University if he'd do a video on the EcoTrac system and he said he would if he could get his hands on one to tear down. He did do the ZF 9-speed transmission in the Cherokee. This is an excellent set of videos if you have not seen them yet.



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post #47 of 48 (permalink) Old 03-15-2017, 08:00 PM
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After a lot of research I can tell you how they switch 100% torque to the rear axle. Yes, the front is direct drive. When the rear clutch is fully locked this provides power to front and rear 50:50. But since torque is related to movement and not power, if the front wheels have no traction and are spinning freely but the rears have full traction, the power is still split 50:50 but torque is at 100% to the rears. It's all in the wording....

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Cheers, Dave.


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post #48 of 48 (permalink) Old 03-15-2017, 09:00 PM
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An easy to visualize example is a human and a torque wrench and a nut. The human can exert power to the torque wrench turning a nut, but until the nut gains traction, the torque wrench will read almost zero.
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