Selec-trac vs command-trac

Maxwellfish

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For the heck of it:

Yes a few iterations of this question have been asked, however not specifically comparing these two transfer cases...

So what are some pros and cons between the two, including how will each hold up? Also, will selec-trac in its part time 4hi & 4lo mores perform the same as the command-trac??

((for fun and educational purposes))
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macintux

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Well, @The Great Grape Ape as I recall had some feelings about the specific Selec-Trac that's being used (there are two different versions of it), so maybe he'll see this ping.

The crawl ratio is different: 4:1 for Rubicon, 2.73:1 IIRC for everything else.

4H and 4L should be identical, other than crawl ratio.

And please, please, please don't let this devolve into another "my preference is better than yours" thread. Please.
 

macintux

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Maxwellfish

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Are you sure the existing threads don't cover what you need? There are literally hundreds of posts; obviously many of them are bickering, but still, lots of information out there.

https://www.jlwranglerforums.com/forum/threads/selec-trac-full-time-4x4-4wd-system-discussions.1267/
https://www.jlwranglerforums.com/fo...-spin-differential-rear-axle-vs-rubicon.2575/
Thank you. I will read through them again. Many of them devolved and/or focused on driving experience.

I was most interested in If anything was lost by choosing selec-trac over command-trac. (Like if part time modes were truly identical across these two systems?)

Thanks for the direction
 

macintux

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A few of the more useful notes:

https://www.jlwranglerforums.com/fo...me-4x4-4wd-system-discussions.1267/#post-7240
https://www.jlwranglerforums.com/fo...-4wd-system-discussions.1267/page-2#post-7246

This page in particular had several interesting technical posts:

https://www.jlwranglerforums.com/fo...l-time-4x4-4wd-system-discussions.1267/page-3

Grape Ape posted this link to a comprehensive list of all Jeep transfer cases, hadn't seen this before, now I have more reading:

http://www.fourwheeler.com/how-to/transmission-drivetrain/154-1201-jp-guide-to-jeep-transfer-cases/

Unfortunately LSD, BLD, and lockers make the topic even more complicated. You have entered a rabbit hole of infinite depth.
 
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Maxwellfish

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A few of the more useful notes:

https://www.jlwranglerforums.com/fo...me-4x4-4wd-system-discussions.1267/#post-7240
https://www.jlwranglerforums.com/fo...-4wd-system-discussions.1267/page-2#post-7246

This page in particular had several interesting technical posts:

https://www.jlwranglerforums.com/fo...l-time-4x4-4wd-system-discussions.1267/page-3

Grape Ape posted this link to a comprehensive list of all Jeep transfer cases, hadn't seen this before, now I have more reading:

http://www.fourwheeler.com/how-to/transmission-drivetrain/154-1201-jp-guide-to-jeep-transfer-cases/

Unfortunately LSD, BLD, and lockers make the topic even more complicated. You have entered a rabbit hole of infinite depth.
Thank you again. I think you helped narrow my underlying curiosity even further...

Because most (All?) of those posts refrenced/assumed the chain driven version of selec-trac, how does the clutch version "selec -trac ii "compare to the command trac? Especially as it pertains to their 4h/4l modes?

See we are getting somewhere!
 

macintux

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Thank you again. I think you helped narrow my underlying curiosity even further...

Because most (All?) of those posts refrenced/assumed the chain driven version of selec-trac, how does the clutch version "selec -trac ii "compare to the command trac? Especially as it pertains to their 4h/4l modes?

See we are getting somewhere!
This is where I'm hoping someone with a clue will step in. I'm just a kibitzer.
 

AlexK

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Because most (All?) of those posts refrenced/assumed the chain driven version of selec-trac, how does the clutch version "selec -trac ii "compare to the command trac? Especially as it pertains to their 4h/4l modes?
The MP3022 is still a chain-driven transfer case. The electronically-controlled clutch effectively engages the chain drive to send torque to the front wheels as conditions dictate. On the JL, Selec-Trac gives you 2H, 4H Auto, 4H and 4L modes.
 

JDaPP

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To be honest I am more familiar with nv-242 version of selec-trac. Most of the discussions on it were that it was slightly weaker than the command track but I never truly saw hard evidence of it. It usually was someone with command trac talking about theirs being better with a story of a friend's issue, usually followed by people who actually had selec-trac disputing it. My guess is truly hardcore rock climbing may not be its best fit but outside of that I am sure it is dependable.

For the mp 3022 it was on the gen 2 liberty (slightly different iteration). In general on the liberty forums I am on I haven't seen any complaints/issues. Jeep has been using clutch 4wd systems for awhile so I assume they would a decent handle on it...

To answer your question on same functions, this iteration is somewhat new so more data is needed but I don't really see how 4hi and 4lo will be different other than the ratios/crawl speeds.
 
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Maxwellfish

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To be honest I am more familiar with nv-242 version of selec-trac. Most of the discussions on it were that it was slightly weaker than the command track but I never truly saw hard evidence of it. It usually was someone with command trac talking about theirs being better with a story of a friend's issue, usually followed by people who actually had selec-trac disputing it. My guess is truly hardcore rock climbing may not be its best fit but outside of that I am sure it is dependable.

For the mp 3022 it was on the gen 2 liberty (slightly different iteration). In general on the liberty forums I am on I haven't seen any complaints/issues. Jeep has been using clutch 4wd systems for awhile so I assume they would a decent handle on it...

To answer your question on same functions, this iteration is somewhat new so more data is needed but I don't really see how 4hi and 4lo will be different other than the ratios/crawl speeds.
Thank you. Between the two: Are part time modes just accomplished in different methods of locking front and rear axles?

Do we have any information on the new selec trac? Is it truly selec-trac ii? Or yet another generation/ version?
 

JDaPP

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If I am understanding your question the easy answer is yes.
For selec-trac (original) it had a locking center differential which would allow the required "slippage" for pavement usage. I have thought of it as a limited slip for the 4wd. In 4 hi/lo it locks them together same as command trac
Command trac locks the front and back with no ability to "slip"
Big thing is these are all mechanical, pull lever-moves linkage-moves switch on transfer case-locked.

To be honest I really don't know that much on the mp3022(used on liberty (2008-2012) and current Durango), my understanding of the mp 3022 is it uses clutch packs rather than the center differential method (don't believe it has a center differential). Although this transfer case has been used for awhile this is the first iteration with a 4hi function so I am not sure if the difference is mechanical or strictly computer programming. One thing I will point out is in liberty it was controlled by dial. From what I can tell this very similar to many other 4x4 systems made by other manufacturers. I have not found really any complaints but also don't know if that is because primary use has been on road or if it is just a reliable system.

For me, my only real complaint is computer vs mechanical. I prefer select trac because it provided power 48/50 in auto. Selec trac ii the computer transfers power when the computer decides. I am sure it will be a great system I just like the original better. Couple of links below that might be useful and hopefully someone more knowledgeable than me will chime in.

https://en.m.wikipedia.org/wiki/Jeep_four-wheel-drive_systems#Command-Trac
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25830
 
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Maxwellfish

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If I am understanding your question the easy answer is yes.
For selec-trac (original) it had a locking center differential which would allow the required "slippage" for pavement usage. I have thought of it as a limited slip for the 4wd. In 4 hi/lo it locks them together same as command trac
Command trac locks the front and back with no ability to "slip"
Big thing is these are all mechanical, pull lever-moves linkage-moves switch on transfer case-locked.

To be honest I really don't know that much on the mp3022(used on liberty (2008-2012) and current Durango), my understanding of the mp 3022 is it uses clutch packs rather than the center differential method (don't believe it has a center differential). Although this transfer case has been used for awhile this is the first iteration with a 4hi function so I am not sure if the difference is mechanical or strictly computer programming. One thing I will point out is in liberty it was controlled by dial. From what I can tell this very similar to many other 4x4 systems made by other manufacturers. I have not found really any complaints but also don't know if that is because primary use has been on road or if it is just a reliable system.

For me, my only real complaint is computer vs mechanical. I prefer select trac because it provided power 48/50 in auto. Selec trac ii the computer transfers power when the computer decides. I am sure it will be a great system I just like the original better. Couple of links below that might be useful and hopefully someone more knowledgeable than me will chime in.

https://en.m.wikipedia.org/wiki/Jeep_four-wheel-drive_systems#Command-Trac
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=25830
Thanks. Awesome info
 

AlexK

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my understanding of the mp 3022 is it uses clutch packs rather than the center differential method (don't believe it has a center differential)
Correct, no centre differential as such, an electronically controlled clutch directs torque to the front axle on demand. In 4H Auto, it sends 100% torque to the rear wheels, but as slip is detected it can send up to 50% to the front. In 4H (non Auto) and 4L modes, torque is split 50/50 front/rear. Gear reduction for 4L (2.72:1) is by planetary gear set.
 

The Great Grape Ape

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Well, I see this has been mostly covered by AlexK and JDaPP, I was without good internet over the holidays so didn’t want to reply to Mac’s post until back in the city. Only a few more granular things to add anyways, the gist has been covered.

First to clear up, the Lo range on both CommandTrac and SelecTrac (whether v1 or 2) are all 2.73:1 commonly called 2.72:1 , only RockTrac is 4:1. The JL will get SelecTrac-II / MP3022, therefore it will have 2.73:1 Lo just like CommandTrac. So all Saharas will have the same crawl ratios when otherwise configured similarly. Of course different axles (either due to diesel or aftermarket) will change things as will auto vs manual, but same transmission+axle will give you same Lo range ratio across the board.

Second, beyond the numbering we don’t know if & what refreshes were made to the MP3022 for the JL. At the very least they have added a 4Hi option not found on the Liberty, and added 2H & 4H to the Durangos implementation. Also it’s a physical shifter unlike the other’s toggle switch (Liberty) or rotary dial (Durango), and has a neutral position not pencil/pen/pin activated Neutral button like the others.

The MP3022 has a few benefits for on-road driving in how its wet clutch system is controlled electronically, and can alter it’s FT application torque split electronically if Jeep decides to implement that (haven’t see that as a Liberty or Durango application yet, but it could be hidden in the Durango, as details remain scant), this allows for speed dependant changing of the torque split to improve application at highway speeds, and also to avoid binding at lower speeds. It can also pre-load the system if it detects variations, which helps improve FT engagement to quicken reaction, however, again it’s unknown if it’s implemented in this application. Unfortunately too much is unknown about the JL’s version/implementation at this time, but the mention of a 50/50 split and not variations makes it seem more rudimentary than what is possible with the platform, so fully imolemented capabilities remain a mystery.

To which, we don’t even have enough info on the torque handling capabilities of the MP3022 for the JL’s SelecTrac! However, it should still be pretty good and I am hoping this refresh got a worthy boost to go along with the Wrangler’s more likely uses vs vehicles like the Liberty & Durango. One concern regarding this point, is that while it sounds great that it has lived alongside the Hemi in the Durango the torque multiplication of the Durango transmission is much lower so that the max torque sent to ST-II from first gear would be higher in the JL implementations whether the 2.0T or 3.6L. The JL has provided a nice boost to the 1st gear ratios of both the manual, and especially the Auto, but this also means more torque sent down the system past the transmission. As we don’t even have torque figures for the Durango application, there’s no way of knowing for sure what if this is any better or the same or (unlikely) worse. If it’s offered on the diesel, then I’ll be more reassured about its capabilities in the gasoline applications, because it would be unlikely that they would mate it to the diesel if it were anywhere near the limit in the gasoline applications.

Now speaking of that, the strength differences between the SlecTrac 1 (not used here but mentioned above) were not inherent in the design, but that the basis for the Jeep NV242 was on the non-reinforced models of the NV241, so they would be similar to pre-2008 in strength, and a stronger model was made for the Hummer. The CommandTrac and RockTrac bith received updates improving strength a bit, with RockTrac being even stronger and receiving the OR designation for NV241OR. So the strength between CommandTrac and SelecTrac would be closer together than the RockTrac wiphich is significantly stronger than both. Just being clear that strength wasn’t based on the type but on their targets.

Finally, and somewhat of my concern, while this transfer case is chain driven, the power is sent to the clutch assembly instead of directly to the output shaft, so it uses a sleeve to ‘lock’ the clutches in Part-Time modes (4Hi / 4Lo) so it’s not truly the same as the NV242 SelecTrac-I or NV241(OR) of CommandTrac/(RockTrac) which has the chain driving the shaft directly, so when it’s locked, it’s LOCKED. The sleeve should provide the outward appearance of the same result as the PartTime modes in CommandTrac and RockTrac, but for serious off-roading it may be a challenge and again something where a lot of in-the-field / on-the-trail testing will prove-out its capabilities/worthiness. I would be far more comfortable with the NV242 than the MP3022, knowing that it is more like a CommandTrac with FT4WD tacked on than a different implementation.

For people who are using it for on-road/soft-road and light trail driving it should be more than adequate, but for serious Rock Crawling with large tires then it may be a bit of a weakness, but at that point I’d be expecting that user to be going with the RockTrac or a 3rd party like Atlas anyways if they were concerned about bullet-proof.

Information is still limited on all the specs (similar to the lack of detailed info on the Aisin manual transmission) so hopefully when folks like 4Wheeler etc get a chance to do a deep dive, then more info will come to light.

Even if we never find out any more info, I’m confident enough to go the SelecTrac-II/MP3022 route, but without that info it will always stick in my mind as a consideration/concern.

Just FYI, this was our early SelecTrac thread, but it spent most of it’s early posts talking about the NV242, and only much later did we address the reality (unfortunately for many) that the JL was getting the MP3022 instead, so much of the early thread doesn’t really apply anymore, including the extremely high praise which is reserved more for ST-I than ST-II;

https://www.jlwranglerforums.com/forum/threads/selec-trac-full-time-4x4-4wd-system-discussions.1267/

It may be enlightening or just cloud the issue more for some.
 
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