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post #21 of 30 (permalink) Old 09-16-2016, 04:14 PM Thread Starter
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i have a week to decide ...ill check things out first of the week.. have to design my hood now so i can get it finished also going to figure out mounting my lights.. have to run to walmart for some dip and painters tape...
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post #22 of 30 (permalink) Old 09-16-2016, 07:15 PM
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i have a week to decide ...ill check things out first of the week..
If the suspension wasn't damaged, consider swapping in the off-road suspension while you're at it.

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post #23 of 30 (permalink) Old 09-16-2016, 08:26 PM
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Swapping to get low range would not be worth it. Rear two speed diff, 2 speed PTU, control systems, computers, etc... would be a nightmare to ever get it working.

Take th ADII suspension though, thats a definite!!

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post #24 of 30 (permalink) Old 09-16-2016, 09:35 PM
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Swapping to get low range would not be worth it. Rear two speed diff, 2 speed PTU, control systems, computers, etc... would be a nightmare to ever get it working.

Take th ADII suspension though, thats a definite!!

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What would really be cool is getting a TH setup with the rear locker. Extra clearance, a mechanical locker, and a set of tires on a Sport. Sleeper. Oh, yeah!
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post #25 of 30 (permalink) Old 09-17-2016, 10:03 AM
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Since I'm new here and new to my TH, why do people keep mentioning a 2-speed rear diff? If the rear was 2-speed, the front would also have to be also as well as the transfer case. All the wheels have to rotate at the same speed, or something is going to break. I have the locker, but it is my understanding that it just locks the 1/2 shafts together; not change the gear ratio (2-speed)

Also, when I was building my TH on the Jeep web site, my options changed the final drive ratio. There was still another one that I could have picked, but I did not investigate what would happen if I picked it.

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post #26 of 30 (permalink) Old 09-17-2016, 10:49 AM
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@dhh3 - Technically the KL doesn't have a transfer case. The 4x4 KL has what they call a Power Transfer Unit up front and a Rear Drive Module in the rear. Both components are one-speed in AD1 and 2-speed in AD2/ADL. The relationship between the locker and 4WD LOW is the design requires the drive line be in 4WD LOW before it will allow the locker to be engaged.

I posted info on the drive lines you might find interesting: AD1/AD2/ADL Uncovered

BTW, reading the patent closely (link included in the post linked to above) is illuminating and one can't help be impressed how amazing this drivetrain is. The EcoTrac controller is observing numerous inputs including yaw and lateral accelerations to make decisions affecting the TTD engagement that controls how much torque is applied to the front or rear wheels. My impression is a major objective of the entire power/drivetrain is to conserve fuel with the variable valve engine and more, 9-speed tranny, and 4x4 system that tries to stay in FWD as much as possible. Jeep took it and said, let's tweak it to be trail rated.

Last edited by Array; 09-17-2016 at 11:34 AM.
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post #27 of 30 (permalink) Old 09-17-2016, 02:19 PM
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Thank you very much. I am enlightened. I did a google search of a 2-speed rear differential in combination with 4wd and found nothing. I watched 3 you tube videos on the TH, including the one posted on the forum, and now have a basic understanding. According to 4x4 Offroad, the center is a differential.

So, when I choose 4 Low, both the PTO/Center Differential and the rear differential both change to a lower gear ratio?

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post #28 of 30 (permalink) Old 09-17-2016, 02:43 PM
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Thank you very much. I am enlightened. I did a google search of a 2-speed rear differential in combination with 4wd and found nothing. I watched 3 you tube videos on the TH, including the one posted on the forum, and now have a basic understanding. According to 4x4 Offroad, the center is a differential.

So, when I choose 4 Low, both the PTO/Center Differential and the rear differential both change to a lower gear ratio?
Yes, the PTU and RDM both shift and the shift is coordinated by the software. The KL 4x4 does not have a center differential. It does have a three-piece prop shaft:
. It has a TTD (Torque Transfer Device) which is a wet clutch in the RDM (Rear Drive Module). That modulates connection between the PTU and rear differential through slippage or cycled engagement.

Just to add: This is a very unique drive train developed by American Axle. There is not a lot of detail info out there on this concept. That's why the patent document is valuable in understanding how it really works. However, that patent details the hardware. What is NOT divulged is the program code that runs the thing. A person can get their mind boggled when trying to understand how torque is modulated from 60/40 to 40/60 to 0/100 front to rear; while keeping torque and power in proper perspective.
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post #29 of 30 (permalink) Old 09-17-2016, 03:44 PM
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@dhh3 - I made some edits to my previous post to reduce confusion due to the way I originally responded to your question.

Another aspect of this drive train that is really interesting is how it accomplishes the shift to and from FWD and 4WD HIGH. First of all from a power flow standpoint, the PTU is between the transmission and the front differential. This is detailed in the patent document. So the power flow is engine, torque converter, transmission, Power Transfer Unit, then the power can split to the front differential and through the prop shaft to the RDM which contains the rear differential. It's amazing they were able to squeeze in an engine, torque converter, transmission, PTU and front differential in an east/west orientation. In normal drive mode (not Neutral Mode) the PTU engages the prop shaft with a dog clutch with no synchronizer mechanism. In order for it to shift from FWD to 4x4 it must bring the prop shaft up to speed. I does this by engaging the TTD clutch (Torque Transfer Device) in the RDM. Once a sensor detects the shaft is up to speed, the software completes the shift by engaging the PTU's dog clutch. Voila - 4x4. I've heard that there are times the software will stage the shift to 4x4 in anticipation but may not actually go into 4x4. The prop shaft may be spun up, but it's not in 4x4 until that PTU dog clutch is engaged. Once it's in 4WD HIGH mode, it can disengage the TTD clutch completely so it's in FWD but the prop shaft is turning. Then the TTD clutch can be modulated to accomplish different drive train behaviours including moving more torque to the rear wheels for a somewhat RWD feel. (I am not a physics major, so don't ask me how torque is made stronger in the rear versus the front when there is no clutch up front. It may have to do with the relationship between power and torque and the pulsing of the TTD. )

Neutral Mode is a separate function in the PTU and RDM; more associated with the 4WD LOW shift you were asking about. AD2 and ADL can shift into Neutral Mode and those shift mechanisms are the ones that shift from HIGH to LOW to Neutral.

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Last edited by Array; 09-17-2016 at 03:49 PM.
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post #30 of 30 (permalink) Old 09-18-2016, 07:22 AM
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All this is Great Stuff. Thank you for the information. I guess I still have a lot of reading to do.

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